gh-76785: Fixes for test.support.interpreters (gh-112982)

This involves a number of changes for PEP 734.

.github/CODEOWNERS

@@ -78,6 +78,11 @@ Python/traceback.c            @iritkatriel
 **/*importlib/resources/*      @jaraco @warsaw @FFY00
 **/importlib/metadata/*       @jaraco @warsaw
 
+# Subinterpreters
+Lib/test/support/interpreters/**  @ericsnowcurrently
+Modules/_xx*interp*module.c   @ericsnowcurrently
+Lib/test/test_interpreters/**  @ericsnowcurrently
+
 # Dates and times
 **/*datetime*                 @pganssle @abalkin
 **/*str*time*                 @pganssle @abalkin
@@ -148,7 +153,15 @@ Doc/c-api/stable.rst          @encukou
 **/*itertools*                @rhettinger
 **/*collections*              @rhettinger
 **/*random*                   @rhettinger
-**/*queue*                    @rhettinger
+Doc/**/*queue*                @rhettinger
+PCbuild/**/*queue*            @rhettinger
+Modules/_queuemodule.c        @rhettinger
+Lib/*queue*.py                @rhettinger
+Lib/asyncio/*queue*.py        @rhettinger
+Lib/multiprocessing/*queue*.py  @rhettinger
+Lib/test/*queue*.py           @rhettinger
+Lib/test_asyncio/*queue*.py   @rhettinger
+Lib/test_multiprocessing/*queue*.py  @rhettinger
 **/*bisect*                   @rhettinger
 **/*heapq*                    @rhettinger
 **/*functools*                @rhettinger

Include/internal/pycore_crossinterp.h

@@ -11,6 +11,13 @@ extern "C" {
 #include "pycore_lock.h"            // PyMutex
 #include "pycore_pyerrors.h"
 
+/**************/
+/* exceptions */
+/**************/
+
+PyAPI_DATA(PyObject *) PyExc_InterpreterError;
+PyAPI_DATA(PyObject *) PyExc_InterpreterNotFoundError;
+
 
 /***************************/
 /* cross-interpreter calls */
@@ -160,6 +167,9 @@ struct _xi_state {
 extern PyStatus _PyXI_Init(PyInterpreterState *interp);
 extern void _PyXI_Fini(PyInterpreterState *interp);
 
+extern PyStatus _PyXI_InitTypes(PyInterpreterState *interp);
+extern void _PyXI_FiniTypes(PyInterpreterState *interp);
+
 
 /***************************/
 /* short-term data sharing */

Include/internal/pycore_interp.h

@@ -250,9 +250,9 @@ _PyInterpreterState_SetFinalizing(PyInterpreterState *interp, PyThreadState *tst
 // Export for the _xxinterpchannels module.
 PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(int64_t);
 
-extern int _PyInterpreterState_IDInitref(PyInterpreterState *);
+PyAPI_FUNC(int) _PyInterpreterState_IDInitref(PyInterpreterState *);
-extern int _PyInterpreterState_IDIncref(PyInterpreterState *);
+PyAPI_FUNC(int) _PyInterpreterState_IDIncref(PyInterpreterState *);
-extern void _PyInterpreterState_IDDecref(PyInterpreterState *);
+PyAPI_FUNC(void) _PyInterpreterState_IDDecref(PyInterpreterState *);
 
 extern const PyConfig* _PyInterpreterState_GetConfig(PyInterpreterState *interp);
 

Lib/test/support/interpreters/__init__.py

@@ -0,0 +1,160 @@
+"""Subinterpreters High Level Module."""
+
+import threading
+import weakref
+import _xxsubinterpreters as _interpreters
+
+# aliases:
+from _xxsubinterpreters import (
+    InterpreterError, InterpreterNotFoundError,
+    is_shareable,
+)
+
+
+__all__ = [
+    'get_current', 'get_main', 'create', 'list_all', 'is_shareable',
+    'Interpreter',
+    'InterpreterError', 'InterpreterNotFoundError', 'ExecFailure',
+    'create_queue', 'Queue', 'QueueEmpty', 'QueueFull',
+]
+
+
+_queuemod = None
+
+def __getattr__(name):
+    if name in ('Queue', 'QueueEmpty', 'QueueFull', 'create_queue'):
+        global create_queue, Queue, QueueEmpty, QueueFull
+        ns = globals()
+        from .queues import (
+            create as create_queue,
+            Queue, QueueEmpty, QueueFull,
+        )
+        return ns[name]
+    else:
+        raise AttributeError(name)
+
+
+class ExecFailure(RuntimeError):
+
+    def __init__(self, excinfo):
+        msg = excinfo.formatted
+        if not msg:
+            if excinfo.type and snapshot.msg:
+                msg = f'{snapshot.type.__name__}: {snapshot.msg}'
+            else:
+                msg = snapshot.type.__name__ or snapshot.msg
+        super().__init__(msg)
+        self.snapshot = excinfo
+
+
+def create():
+    """Return a new (idle) Python interpreter."""
+    id = _interpreters.create(isolated=True)
+    return Interpreter(id)
+
+
+def list_all():
+    """Return all existing interpreters."""
+    return [Interpreter(id) for id in _interpreters.list_all()]
+
+
+def get_current():
+    """Return the currently running interpreter."""
+    id = _interpreters.get_current()
+    return Interpreter(id)
+
+
+def get_main():
+    """Return the main interpreter."""
+    id = _interpreters.get_main()
+    return Interpreter(id)
+
+
+_known = weakref.WeakValueDictionary()
+
+class Interpreter:
+    """A single Python interpreter."""
+
+    def __new__(cls, id, /):
+        # There is only one instance for any given ID.
+        if not isinstance(id, int):
+            raise TypeError(f'id must be an int, got {id!r}')
+        id = int(id)
+        try:
+            self = _known[id]
+            assert hasattr(self, '_ownsref')
+        except KeyError:
+            # This may raise InterpreterNotFoundError:
+            _interpreters._incref(id)
+            try:
+                self = super().__new__(cls)
+                self._id = id
+                self._ownsref = True
+            except BaseException:
+                _interpreters._deccref(id)
+                raise
+            _known[id] = self
+        return self
+
+    def __repr__(self):
+        return f'{type(self).__name__}({self.id})'
+
+    def __hash__(self):
+        return hash(self._id)
+
+    def __del__(self):
+        self._decref()
+
+    def _decref(self):
+        if not self._ownsref:
+            return
+        self._ownsref = False
+        try:
+            _interpreters._decref(self.id)
+        except InterpreterNotFoundError:
+            pass
+
+    @property
+    def id(self):
+        return self._id
+
+    def is_running(self):
+        """Return whether or not the identified interpreter is running."""
+        return _interpreters.is_running(self._id)
+
+    def close(self):
+        """Finalize and destroy the interpreter.
+
+        Attempting to destroy the current interpreter results
+        in a RuntimeError.
+        """
+        return _interpreters.destroy(self._id)
+
+    def exec_sync(self, code, /, channels=None):
+        """Run the given source code in the interpreter.
+
+        This is essentially the same as calling the builtin "exec"
+        with this interpreter, using the __dict__ of its __main__
+        module as both globals and locals.
+
+        There is no return value.
+
+        If the code raises an unhandled exception then an ExecFailure
+        is raised, which summarizes the unhandled exception.  The actual
+        exception is discarded because objects cannot be shared between
+        interpreters.
+
+        This blocks the current Python thread until done.  During
+        that time, the previous interpreter is allowed to run
+        in other threads.
+        """
+        excinfo = _interpreters.exec(self._id, code, channels)
+        if excinfo is not None:
+            raise ExecFailure(excinfo)
+
+    def run(self, code, /, channels=None):
+        def task():
+            self.exec_sync(code, channels=channels)
+        t = threading.Thread(target=task)
+        t.start()
+        return t

Lib/test/support/interpreters/channels.py

@@ -1,11 +1,9 @@
-"""Subinterpreters High Level Module."""
+"""Cross-interpreter Channels High Level Module."""
 
 import time
-import _xxsubinterpreters as _interpreters
 import _xxinterpchannels as _channels
 
 # aliases:
-from _xxsubinterpreters import is_shareable
 from _xxinterpchannels import (
     ChannelError, ChannelNotFoundError, ChannelClosedError,
     ChannelEmptyError, ChannelNotEmptyError,
@@ -13,123 +11,13 @@ from _xxinterpchannels import (
 
 
 __all__ = [
-    'Interpreter', 'get_current', 'get_main', 'create', 'list_all',
+    'create', 'list_all',
-    'RunFailedError',
     'SendChannel', 'RecvChannel',
-    'create_channel', 'list_all_channels', 'is_shareable',
+    'ChannelError', 'ChannelNotFoundError', 'ChannelEmptyError',
-    'ChannelError', 'ChannelNotFoundError',
+]
-    'ChannelEmptyError',
-    ]
 
 
-class RunFailedError(RuntimeError):
+def create():
-
-    def __init__(self, excinfo):
-        msg = excinfo.formatted
-        if not msg:
-            if excinfo.type and snapshot.msg:
-                msg = f'{snapshot.type.__name__}: {snapshot.msg}'
-            else:
-                msg = snapshot.type.__name__ or snapshot.msg
-        super().__init__(msg)
-        self.snapshot = excinfo
-
-
-def create(*, isolated=True):
-    """Return a new (idle) Python interpreter."""
-    id = _interpreters.create(isolated=isolated)
-    return Interpreter(id, isolated=isolated)
-
-
-def list_all():
-    """Return all existing interpreters."""
-    return [Interpreter(id) for id in _interpreters.list_all()]
-
-
-def get_current():
-    """Return the currently running interpreter."""
-    id = _interpreters.get_current()
-    return Interpreter(id)
-
-
-def get_main():
-    """Return the main interpreter."""
-    id = _interpreters.get_main()
-    return Interpreter(id)
-
-
-class Interpreter:
-    """A single Python interpreter."""
-
-    def __init__(self, id, *, isolated=None):
-        if not isinstance(id, (int, _interpreters.InterpreterID)):
-            raise TypeError(f'id must be an int, got {id!r}')
-        self._id = id
-        self._isolated = isolated
-
-    def __repr__(self):
-        data = dict(id=int(self._id), isolated=self._isolated)
-        kwargs = (f'{k}={v!r}' for k, v in data.items())
-        return f'{type(self).__name__}({", ".join(kwargs)})'
-
-    def __hash__(self):
-        return hash(self._id)
-
-    def __eq__(self, other):
-        if not isinstance(other, Interpreter):
-            return NotImplemented
-        else:
-            return other._id == self._id
-
-    @property
-    def id(self):
-        return self._id
-
-    @property
-    def isolated(self):
-        if self._isolated is None:
-            # XXX The low-level function has not been added yet.
-            # See bpo-....
-            self._isolated = _interpreters.is_isolated(self._id)
-        return self._isolated
-
-    def is_running(self):
-        """Return whether or not the identified interpreter is running."""
-        return _interpreters.is_running(self._id)
-
-    def close(self):
-        """Finalize and destroy the interpreter.
-
-        Attempting to destroy the current interpreter results
-        in a RuntimeError.
-        """
-        return _interpreters.destroy(self._id)
-
-    # XXX Rename "run" to "exec"?
-    def run(self, src_str, /, channels=None):
-        """Run the given source code in the interpreter.
-
-        This is essentially the same as calling the builtin "exec"
-        with this interpreter, using the __dict__ of its __main__
-        module as both globals and locals.
-
-        There is no return value.
-
-        If the code raises an unhandled exception then a RunFailedError
-        is raised, which summarizes the unhandled exception.  The actual
-        exception is discarded because objects cannot be shared between
-        interpreters.
-
-        This blocks the current Python thread until done.  During
-        that time, the previous interpreter is allowed to run
-        in other threads.
-        """
-        excinfo = _interpreters.exec(self._id, src_str, channels)
-        if excinfo is not None:
-            raise RunFailedError(excinfo)
-
-
-def create_channel():
     """Return (recv, send) for a new cross-interpreter channel.
 
     The channel may be used to pass data safely between interpreters.
@@ -139,7 +27,7 @@ def create_channel():
     return recv, send
 
 
-def list_all_channels():
+def list_all():
     """Return a list of (recv, send) for all open channels."""
     return [(RecvChannel(cid), SendChannel(cid))
             for cid in _channels.list_all()]

Lib/test/support/interpreters/queues.py

@@ -0,0 +1,156 @@
+"""Cross-interpreter Queues High Level Module."""
+
+import queue
+import time
+import weakref
+import _xxinterpchannels as _channels
+import _xxinterpchannels as _queues
+
+# aliases:
+from _xxinterpchannels import (
+    ChannelError as QueueError,
+    ChannelNotFoundError as QueueNotFoundError,
+)
+
+__all__ = [
+    'create', 'list_all',
+    'Queue',
+    'QueueError', 'QueueNotFoundError', 'QueueEmpty', 'QueueFull',
+]
+
+
+def create(maxsize=0):
+    """Return a new cross-interpreter queue.
+
+    The queue may be used to pass data safely between interpreters.
+    """
+    # XXX honor maxsize
+    qid = _queues.create()
+    return Queue._with_maxsize(qid, maxsize)
+
+
+def list_all():
+    """Return a list of all open queues."""
+    return [Queue(qid)
+            for qid in _queues.list_all()]
+
+
+class QueueEmpty(queue.Empty):
+    """Raised from get_nowait() when the queue is empty.
+
+    It is also raised from get() if it times out.
+    """
+
+
+class QueueFull(queue.Full):
+    """Raised from put_nowait() when the queue is full.
+
+    It is also raised from put() if it times out.
+    """
+
+
+_known_queues = weakref.WeakValueDictionary()
+
+class Queue:
+    """A cross-interpreter queue."""
+
+    @classmethod
+    def _with_maxsize(cls, id, maxsize):
+        if not isinstance(maxsize, int):
+            raise TypeError(f'maxsize must be an int, got {maxsize!r}')
+        elif maxsize < 0:
+            maxsize = 0
+        else:
+            maxsize = int(maxsize)
+        self = cls(id)
+        self._maxsize = maxsize
+        return self
+
+    def __new__(cls, id, /):
+        # There is only one instance for any given ID.
+        if isinstance(id, int):
+            id = _channels._channel_id(id, force=False)
+        elif not isinstance(id, _channels.ChannelID):
+            raise TypeError(f'id must be an int, got {id!r}')
+        key = int(id)
+        try:
+            self = _known_queues[key]
+        except KeyError:
+            self = super().__new__(cls)
+            self._id = id
+            self._maxsize = 0
+            _known_queues[key] = self
+        return self
+
+    def __repr__(self):
+        return f'{type(self).__name__}({self.id})'
+
+    def __hash__(self):
+        return hash(self._id)
+
+    @property
+    def id(self):
+        return int(self._id)
+
+    @property
+    def maxsize(self):
+        return self._maxsize
+
+    @property
+    def _info(self):
+        return _channels.get_info(self._id)
+
+    def empty(self):
+        return self._info.count == 0
+
+    def full(self):
+        if self._maxsize <= 0:
+            return False
+        return self._info.count >= self._maxsize
+
+    def qsize(self):
+        return self._info.count
+
+    def put(self, obj, timeout=None):
+        # XXX block if full
+        _channels.send(self._id, obj, blocking=False)
+
+    def put_nowait(self, obj):
+        # XXX raise QueueFull if full
+        return _channels.send(self._id, obj, blocking=False)
+
+    def get(self, timeout=None, *,
+             _sentinel=object(),
+             _delay=10 / 1000,  # 10 milliseconds
+             ):
+        """Return the next object from the queue.
+
+        This blocks while the queue is empty.
+        """
+        if timeout is not None:
+            timeout = int(timeout)
+            if timeout < 0:
+                raise ValueError(f'timeout value must be non-negative')
+            end = time.time() + timeout
+        obj = _channels.recv(self._id, _sentinel)
+        while obj is _sentinel:
+            time.sleep(_delay)
+            if timeout is not None and time.time() >= end:
+                raise QueueEmpty
+            obj = _channels.recv(self._id, _sentinel)
+        return obj
+
+    def get_nowait(self, *, _sentinel=object()):
+        """Return the next object from the channel.
+
+        If the queue is empty then raise QueueEmpty.  Otherwise this
+        is the same as get().
+        """
+        obj = _channels.recv(self._id, _sentinel)
+        if obj is _sentinel:
+            raise QueueEmpty
+        return obj
+
+
+# XXX add this:
+#_channels._register_queue_type(Queue)

Lib/test/test__xxinterpchannels.py

@@ -79,8 +79,7 @@ class Interpreter(namedtuple('Interpreter', 'name id')):
                 name = 'interp'
             elif name == 'main':
                 raise ValueError('name mismatch (unexpected "main")')
-            if not isinstance(id, interpreters.InterpreterID):
+            assert isinstance(id, int), repr(id)
-                id = interpreters.InterpreterID(id)
         elif not name or name == 'main':
             name = 'main'
             id = main

Lib/test/test__xxsubinterpreters.py

@@ -15,6 +15,7 @@ from test.support import script_helper
 
 
 interpreters = import_helper.import_module('_xxsubinterpreters')
+from _xxsubinterpreters import InterpreterNotFoundError
 
 
 ##################################
@@ -266,7 +267,7 @@ class GetCurrentTests(TestBase):
         main = interpreters.get_main()
         cur = interpreters.get_current()
         self.assertEqual(cur, main)
-        self.assertIsInstance(cur, interpreters.InterpreterID)
+        self.assertIsInstance(cur, int)
 
     def test_subinterpreter(self):
         main = interpreters.get_main()
@@ -275,7 +276,7 @@ class GetCurrentTests(TestBase):
             import _xxsubinterpreters as _interpreters
             cur = _interpreters.get_current()
             print(cur)
-            assert isinstance(cur, _interpreters.InterpreterID)
+            assert isinstance(cur, int)
             """))
         cur = int(out.strip())
         _, expected = interpreters.list_all()
@@ -289,7 +290,7 @@ class GetMainTests(TestBase):
         [expected] = interpreters.list_all()
         main = interpreters.get_main()
         self.assertEqual(main, expected)
-        self.assertIsInstance(main, interpreters.InterpreterID)
+        self.assertIsInstance(main, int)
 
     def test_from_subinterpreter(self):
         [expected] = interpreters.list_all()
@@ -298,7 +299,7 @@ class GetMainTests(TestBase):
             import _xxsubinterpreters as _interpreters
             main = _interpreters.get_main()
             print(main)
-            assert isinstance(main, _interpreters.InterpreterID)
+            assert isinstance(main, int)
             """))
         main = int(out.strip())
         self.assertEqual(main, expected)
@@ -333,11 +334,11 @@ class IsRunningTests(TestBase):
     def test_already_destroyed(self):
         interp = interpreters.create()
         interpreters.destroy(interp)
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.is_running(interp)
 
     def test_does_not_exist(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.is_running(1_000_000)
 
     def test_bad_id(self):
@@ -345,70 +346,11 @@ class IsRunningTests(TestBase):
             interpreters.is_running(-1)
 
 
-class InterpreterIDTests(TestBase):
-
-    def test_with_int(self):
-        id = interpreters.InterpreterID(10, force=True)
-
-        self.assertEqual(int(id), 10)
-
-    def test_coerce_id(self):
-        class Int(str):
-            def __index__(self):
-                return 10
-
-        id = interpreters.InterpreterID(Int(), force=True)
-        self.assertEqual(int(id), 10)
-
-    def test_bad_id(self):
-        self.assertRaises(TypeError, interpreters.InterpreterID, object())
-        self.assertRaises(TypeError, interpreters.InterpreterID, 10.0)
-        self.assertRaises(TypeError, interpreters.InterpreterID, '10')
-        self.assertRaises(TypeError, interpreters.InterpreterID, b'10')
-        self.assertRaises(ValueError, interpreters.InterpreterID, -1)
-        self.assertRaises(OverflowError, interpreters.InterpreterID, 2**64)
-
-    def test_does_not_exist(self):
-        id = interpreters.create()
-        with self.assertRaises(RuntimeError):
-            interpreters.InterpreterID(int(id) + 1)  # unforced
-
-    def test_str(self):
-        id = interpreters.InterpreterID(10, force=True)
-        self.assertEqual(str(id), '10')
-
-    def test_repr(self):
-        id = interpreters.InterpreterID(10, force=True)
-        self.assertEqual(repr(id), 'InterpreterID(10)')
-
-    def test_equality(self):
-        id1 = interpreters.create()
-        id2 = interpreters.InterpreterID(int(id1))
-        id3 = interpreters.create()
-
-        self.assertTrue(id1 == id1)
-        self.assertTrue(id1 == id2)
-        self.assertTrue(id1 == int(id1))
-        self.assertTrue(int(id1) == id1)
-        self.assertTrue(id1 == float(int(id1)))
-        self.assertTrue(float(int(id1)) == id1)
-        self.assertFalse(id1 == float(int(id1)) + 0.1)
-        self.assertFalse(id1 == str(int(id1)))
-        self.assertFalse(id1 == 2**1000)
-        self.assertFalse(id1 == float('inf'))
-        self.assertFalse(id1 == 'spam')
-        self.assertFalse(id1 == id3)
-
-        self.assertFalse(id1 != id1)
-        self.assertFalse(id1 != id2)
-        self.assertTrue(id1 != id3)
-
-
 class CreateTests(TestBase):
 
     def test_in_main(self):
         id = interpreters.create()
-        self.assertIsInstance(id, interpreters.InterpreterID)
+        self.assertIsInstance(id, int)
 
         self.assertIn(id, interpreters.list_all())
 
@@ -444,7 +386,7 @@ class CreateTests(TestBase):
             import _xxsubinterpreters as _interpreters
             id = _interpreters.create()
             print(id)
-            assert isinstance(id, _interpreters.InterpreterID)
+            assert isinstance(id, int)
             """))
         id2 = int(out.strip())
 
@@ -536,11 +478,11 @@ class DestroyTests(TestBase):
     def test_already_destroyed(self):
         id = interpreters.create()
         interpreters.destroy(id)
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.destroy(id)
 
     def test_does_not_exist(self):
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.destroy(1_000_000)
 
     def test_bad_id(self):
@@ -741,7 +683,7 @@ class RunStringTests(TestBase):
         id = 0
         while id in interpreters.list_all():
             id += 1
-        with self.assertRaises(RuntimeError):
+        with self.assertRaises(InterpreterNotFoundError):
             interpreters.run_string(id, 'print("spam")')
 
     def test_error_id(self):

Lib/test/test_capi/test_misc.py

@@ -1527,6 +1527,7 @@ class TestPendingCalls(unittest.TestCase):
         maxtext = 250
         main_interpid = 0
         interpid = _interpreters.create()
+        self.addCleanup(lambda: _interpreters.destroy(interpid))
         _interpreters.run_string(interpid, f"""if True:
             import json
             import os
@@ -2020,6 +2021,137 @@ class SubinterpreterTest(unittest.TestCase):
         self.assertEqual(main_attr_id, subinterp_attr_id)
 
 
+@requires_subinterpreters
+class InterpreterIDTests(unittest.TestCase):
+
+    InterpreterID = _testcapi.get_interpreterid_type()
+
+    def new_interpreter(self):
+        def ensure_destroyed(interpid):
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        id = _interpreters.create()
+        self.addCleanup(lambda: ensure_destroyed(id))
+        return id
+
+    def test_with_int(self):
+        id = self.InterpreterID(10, force=True)
+
+        self.assertEqual(int(id), 10)
+
+    def test_coerce_id(self):
+        class Int(str):
+            def __index__(self):
+                return 10
+
+        id = self.InterpreterID(Int(), force=True)
+        self.assertEqual(int(id), 10)
+
+    def test_bad_id(self):
+        for badid in [
+            object(),
+            10.0,
+            '10',
+            b'10',
+        ]:
+            with self.subTest(badid):
+                with self.assertRaises(TypeError):
+                    self.InterpreterID(badid)
+
+        badid = -1
+        with self.subTest(badid):
+            with self.assertRaises(ValueError):
+                self.InterpreterID(badid)
+
+        badid = 2**64
+        with self.subTest(badid):
+            with self.assertRaises(OverflowError):
+                self.InterpreterID(badid)
+
+    def test_exists(self):
+        id = self.new_interpreter()
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(int(id) + 1)  # unforced
+
+    def test_does_not_exist(self):
+        id = self.new_interpreter()
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(int(id) + 1)  # unforced
+
+    def test_destroyed(self):
+        id = _interpreters.create()
+        _interpreters.destroy(id)
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            self.InterpreterID(id)  # unforced
+
+    def test_str(self):
+        id = self.InterpreterID(10, force=True)
+        self.assertEqual(str(id), '10')
+
+    def test_repr(self):
+        id = self.InterpreterID(10, force=True)
+        self.assertEqual(repr(id), 'InterpreterID(10)')
+
+    def test_equality(self):
+        id1 = self.new_interpreter()
+        id2 = self.InterpreterID(id1)
+        id3 = self.InterpreterID(
+                self.new_interpreter())
+
+        self.assertTrue(id2 == id2)  # identity
+        self.assertTrue(id2 == id1)  # int-equivalent
+        self.assertTrue(id1 == id2)  # reversed
+        self.assertTrue(id2 == int(id2))
+        self.assertTrue(id2 == float(int(id2)))
+        self.assertTrue(float(int(id2)) == id2)
+        self.assertFalse(id2 == float(int(id2)) + 0.1)
+        self.assertFalse(id2 == str(int(id2)))
+        self.assertFalse(id2 == 2**1000)
+        self.assertFalse(id2 == float('inf'))
+        self.assertFalse(id2 == 'spam')
+        self.assertFalse(id2 == id3)
+
+        self.assertFalse(id2 != id2)
+        self.assertFalse(id2 != id1)
+        self.assertFalse(id1 != id2)
+        self.assertTrue(id2 != id3)
+
+    def test_linked_lifecycle(self):
+        id1 = _interpreters.create()
+        _testcapi.unlink_interpreter_refcount(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        id2 = self.InterpreterID(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            1)
+
+        # The interpreter isn't linked to ID objects, so it isn't destroyed.
+        del id2
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        _testcapi.link_interpreter_refcount(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            0)
+
+        id3 = self.InterpreterID(id1)
+        self.assertEqual(
+            _testinternalcapi.get_interpreter_refcount(id1),
+            1)
+
+        # The interpreter is linked now so is destroyed.
+        del id3
+        with self.assertRaises(_interpreters.InterpreterNotFoundError):
+            _testinternalcapi.get_interpreter_refcount(id1)
+
+
 class BuiltinStaticTypesTests(unittest.TestCase):
 
     TYPES = [

Lib/test/test_import/__init__.py

@@ -1971,6 +1971,7 @@ class SubinterpImportTests(unittest.TestCase):
             print(_testsinglephase)
             ''')
         interpid = _interpreters.create()
+        self.addCleanup(lambda: _interpreters.destroy(interpid))
 
         excsnap = _interpreters.run_string(interpid, script)
         self.assertIsNot(excsnap, None)
@@ -2105,12 +2106,18 @@ class SinglephaseInitTests(unittest.TestCase):
 
     def add_subinterpreter(self):
         interpid = _interpreters.create(isolated=False)
-        _interpreters.run_string(interpid, textwrap.dedent('''
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        _interpreters.exec(interpid, textwrap.dedent('''
             import sys
             import _testinternalcapi
             '''))
         def clean_up():
-            _interpreters.run_string(interpid, textwrap.dedent(f'''
+            _interpreters.exec(interpid, textwrap.dedent(f'''
                 name = {self.NAME!r}
                 if name in sys.modules:
                     sys.modules.pop(name)._clear_globals()

Lib/test/test_importlib/test_util.py

@@ -657,14 +657,26 @@ class IncompatibleExtensionModuleRestrictionsTests(unittest.TestCase):
 
     def run_with_own_gil(self, script):
         interpid = _interpreters.create(isolated=True)
-        excsnap = _interpreters.run_string(interpid, script)
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        excsnap = _interpreters.exec(interpid, script)
         if excsnap is not None:
             if excsnap.type.__name__ == 'ImportError':
                 raise ImportError(excsnap.msg)
 
     def run_with_shared_gil(self, script):
         interpid = _interpreters.create(isolated=False)
-        excsnap = _interpreters.run_string(interpid, script)
+        def ensure_destroyed():
+            try:
+                _interpreters.destroy(interpid)
+            except _interpreters.InterpreterNotFoundError:
+                pass
+        self.addCleanup(ensure_destroyed)
+        excsnap = _interpreters.exec(interpid, script)
         if excsnap is not None:
             if excsnap.type.__name__ == 'ImportError':
                 raise ImportError(excsnap.msg)

Lib/test/test_interpreters/__init__.py

@@ -0,0 +1,5 @@
+import os
+from test.support import load_package_tests
+
+def load_tests(*args):
+    return load_package_tests(os.path.dirname(__file__), *args)

Lib/test/test_interpreters/__main__.py

@@ -0,0 +1,4 @@
+from . import load_tests
+import unittest
+
+nittest.main()

Lib/test/test_interpreters/test_api.py

@@ -0,0 +1,642 @@
+import os
+import threading
+from textwrap import dedent
+import unittest
+
+from test import support
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from test.support import interpreters
+from test.support.interpreters import InterpreterNotFoundError
+from .utils import _captured_script, _run_output, _running, TestBase
+
+
+class ModuleTests(TestBase):
+
+    def test_queue_aliases(self):
+        first = [
+            interpreters.create_queue,
+            interpreters.Queue,
+            interpreters.QueueEmpty,
+            interpreters.QueueFull,
+        ]
+        second = [
+            interpreters.create_queue,
+            interpreters.Queue,
+            interpreters.QueueEmpty,
+            interpreters.QueueFull,
+        ]
+        self.assertEqual(second, first)
+
+
+class CreateTests(TestBase):
+
+    def test_in_main(self):
+        interp = interpreters.create()
+        self.assertIsInstance(interp, interpreters.Interpreter)
+        self.assertIn(interp, interpreters.list_all())
+
+    def test_in_thread(self):
+        lock = threading.Lock()
+        interp = None
+        def f():
+            nonlocal interp
+            interp = interpreters.create()
+            lock.acquire()
+            lock.release()
+        t = threading.Thread(target=f)
+        with lock:
+            t.start()
+        t.join()
+        self.assertIn(interp, interpreters.list_all())
+
+    def test_in_subinterpreter(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent("""
+            from test.support import interpreters
+            interp = interpreters.create()
+            print(interp.id)
+            """))
+        interp2 = interpreters.Interpreter(int(out))
+        self.assertEqual(interpreters.list_all(), [main, interp, interp2])
+
+    def test_after_destroy_all(self):
+        before = set(interpreters.list_all())
+        # Create 3 subinterpreters.
+        interp_lst = []
+        for _ in range(3):
+            interps = interpreters.create()
+            interp_lst.append(interps)
+        # Now destroy them.
+        for interp in interp_lst:
+            interp.close()
+        # Finally, create another.
+        interp = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()), before | {interp})
+
+    def test_after_destroy_some(self):
+        before = set(interpreters.list_all())
+        # Create 3 subinterpreters.
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        interp3 = interpreters.create()
+        # Now destroy 2 of them.
+        interp1.close()
+        interp2.close()
+        # Finally, create another.
+        interp = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()), before | {interp3, interp})
+
+
+class GetMainTests(TestBase):
+
+    def test_id(self):
+        main = interpreters.get_main()
+        self.assertEqual(main.id, 0)
+
+    def test_current(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        self.assertIs(main, current)
+
+    def test_idempotent(self):
+        main1 = interpreters.get_main()
+        main2 = interpreters.get_main()
+        self.assertIs(main1, main2)
+
+
+class GetCurrentTests(TestBase):
+
+    def test_main(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        self.assertEqual(current, main)
+
+    def test_subinterpreter(self):
+        main = interpreters.get_main()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent("""
+            from test.support import interpreters
+            cur = interpreters.get_current()
+            print(cur.id)
+            """))
+        current = interpreters.Interpreter(int(out))
+        self.assertEqual(current, interp)
+        self.assertNotEqual(current, main)
+
+    def test_idempotent(self):
+        with self.subTest('main'):
+            cur1 = interpreters.get_current()
+            cur2 = interpreters.get_current()
+            self.assertIs(cur1, cur2)
+
+        with self.subTest('subinterpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            objid1, objid2 = (int(v) for v in out.splitlines())
+            self.assertEqual(objid1, objid2)
+
+        with self.subTest('per-interpreter'):
+            interp = interpreters.create()
+            out = _run_output(interp, dedent("""
+                from test.support import interpreters
+                cur = interpreters.get_current()
+                print(id(cur))
+                """))
+            id1 = int(out)
+            id2 = id(interp)
+            self.assertNotEqual(id1, id2)
+
+
+class ListAllTests(TestBase):
+
+    def test_initial(self):
+        interps = interpreters.list_all()
+        self.assertEqual(1, len(interps))
+
+    def test_after_creating(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+
+        ids = []
+        for interp in interpreters.list_all():
+            ids.append(interp.id)
+
+        self.assertEqual(ids, [main.id, first.id, second.id])
+
+    def test_after_destroying(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+        first.close()
+
+        ids = []
+        for interp in interpreters.list_all():
+            ids.append(interp.id)
+
+        self.assertEqual(ids, [main.id, second.id])
+
+    def test_idempotent(self):
+        main = interpreters.get_current()
+        first = interpreters.create()
+        second = interpreters.create()
+        expected = [main, first, second]
+
+        actual = interpreters.list_all()
+
+        self.assertEqual(actual, expected)
+        for interp1, interp2 in zip(actual, expected):
+            self.assertIs(interp1, interp2)
+
+
+class InterpreterObjectTests(TestBase):
+
+    def test_init_int(self):
+        interpid = interpreters.get_current().id
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(interp.id, interpid)
+
+    def test_init_interpreter_id(self):
+        interpid = interpreters.get_current()._id
+        interp = interpreters.Interpreter(interpid)
+        self.assertEqual(interp._id, interpid)
+
+    def test_init_unsupported(self):
+        actualid = interpreters.get_current().id
+        for interpid in [
+            str(actualid),
+            float(actualid),
+            object(),
+            None,
+            '',
+        ]:
+            with self.subTest(repr(interpid)):
+                with self.assertRaises(TypeError):
+                    interpreters.Interpreter(interpid)
+
+    def test_idempotent(self):
+        main = interpreters.get_main()
+        interp = interpreters.Interpreter(main.id)
+        self.assertIs(interp, main)
+
+    def test_init_does_not_exist(self):
+        with self.assertRaises(InterpreterNotFoundError):
+            interpreters.Interpreter(1_000_000)
+
+    def test_init_bad_id(self):
+        with self.assertRaises(ValueError):
+            interpreters.Interpreter(-1)
+
+    def test_id_type(self):
+        main = interpreters.get_main()
+        current = interpreters.get_current()
+        interp = interpreters.create()
+        self.assertIsInstance(main.id, int)
+        self.assertIsInstance(current.id, int)
+        self.assertIsInstance(interp.id, int)
+
+    def test_id_readonly(self):
+        interp = interpreters.create()
+        with self.assertRaises(AttributeError):
+            interp.id = 1_000_000
+
+    def test_hashable(self):
+        interp = interpreters.create()
+        expected = hash(interp.id)
+        actual = hash(interp)
+        self.assertEqual(actual, expected)
+
+    def test_equality(self):
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        self.assertEqual(interp1, interp1)
+        self.assertNotEqual(interp1, interp2)
+
+
+class TestInterpreterIsRunning(TestBase):
+
+    def test_main(self):
+        main = interpreters.get_main()
+        self.assertTrue(main.is_running())
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_subinterpreter(self):
+        interp = interpreters.create()
+        self.assertFalse(interp.is_running())
+
+        with _running(interp):
+            self.assertTrue(interp.is_running())
+        self.assertFalse(interp.is_running())
+
+    def test_finished(self):
+        r, w = self.pipe()
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            os.write({w}, b'x')
+            """)
+        self.assertFalse(interp.is_running())
+        self.assertEqual(os.read(r, 1), b'x')
+
+    def test_from_subinterpreter(self):
+        interp = interpreters.create()
+        out = _run_output(interp, dedent(f"""
+            import _xxsubinterpreters as _interpreters
+            if _interpreters.is_running({interp.id}):
+                print(True)
+            else:
+                print(False)
+            """))
+        self.assertEqual(out.strip(), 'True')
+
+    def test_already_destroyed(self):
+        interp = interpreters.create()
+        interp.close()
+        with self.assertRaises(InterpreterNotFoundError):
+            interp.is_running()
+
+    def test_with_only_background_threads(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        DONE = b'D'
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+
+            def task():
+                v = os.read({r_thread}, 1)
+                assert v == {DONE!r}
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            """)
+        self.assertFalse(interp.is_running())
+
+        os.write(w_thread, DONE)
+        interp.exec_sync('t.join()')
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+
+class TestInterpreterClose(TestBase):
+
+    def test_basic(self):
+        main = interpreters.get_main()
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        interp3 = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp2, interp3})
+        interp2.close()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp3})
+
+    def test_all(self):
+        before = set(interpreters.list_all())
+        interps = set()
+        for _ in range(3):
+            interp = interpreters.create()
+            interps.add(interp)
+        self.assertEqual(set(interpreters.list_all()), before | interps)
+        for interp in interps:
+            interp.close()
+        self.assertEqual(set(interpreters.list_all()), before)
+
+    def test_main(self):
+        main, = interpreters.list_all()
+        with self.assertRaises(RuntimeError):
+            main.close()
+
+        def f():
+            with self.assertRaises(RuntimeError):
+                main.close()
+
+        t = threading.Thread(target=f)
+        t.start()
+        t.join()
+
+    def test_already_destroyed(self):
+        interp = interpreters.create()
+        interp.close()
+        with self.assertRaises(InterpreterNotFoundError):
+            interp.close()
+
+    def test_from_current(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        out = _run_output(interp, dedent(f"""
+            from test.support import interpreters
+            interp = interpreters.Interpreter({interp.id})
+            try:
+                interp.close()
+            except RuntimeError:
+                print('failed')
+            """))
+        self.assertEqual(out.strip(), 'failed')
+        self.assertEqual(set(interpreters.list_all()), {main, interp})
+
+    def test_from_sibling(self):
+        main, = interpreters.list_all()
+        interp1 = interpreters.create()
+        interp2 = interpreters.create()
+        self.assertEqual(set(interpreters.list_all()),
+                         {main, interp1, interp2})
+        interp1.exec_sync(dedent(f"""
+            from test.support import interpreters
+            interp2 = interpreters.Interpreter({interp2.id})
+            interp2.close()
+            interp3 = interpreters.create()
+            interp3.close()
+            """))
+        self.assertEqual(set(interpreters.list_all()), {main, interp1})
+
+    def test_from_other_thread(self):
+        interp = interpreters.create()
+        def f():
+            interp.close()
+
+        t = threading.Thread(target=f)
+        t.start()
+        t.join()
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_still_running(self):
+        main, = interpreters.list_all()
+        interp = interpreters.create()
+        with _running(interp):
+            with self.assertRaises(RuntimeError):
+                interp.close()
+            self.assertTrue(interp.is_running())
+
+    def test_subthreads_still_running(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+            import time
+
+            done = False
+
+            def notify_fini():
+                global done
+                done = True
+                t.join()
+            threading._register_atexit(notify_fini)
+
+            def task():
+                while not done:
+                    time.sleep(0.1)
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            """)
+        interp.close()
+
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+
+class TestInterpreterExecSync(TestBase):
+
+    def test_success(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            interp.exec_sync(script)
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    def test_failure(self):
+        interp = interpreters.create()
+        with self.assertRaises(interpreters.ExecFailure):
+            interp.exec_sync('raise Exception')
+
+    def test_in_thread(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            def f():
+                interp.exec_sync(script)
+
+            t = threading.Thread(target=f)
+            t.start()
+            t.join()
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    @support.requires_fork()
+    def test_fork(self):
+        interp = interpreters.create()
+        import tempfile
+        with tempfile.NamedTemporaryFile('w+', encoding='utf-8') as file:
+            file.write('')
+            file.flush()
+
+            expected = 'spam spam spam spam spam'
+            script = dedent(f"""
+                import os
+                try:
+                    os.fork()
+                except RuntimeError:
+                    with open('{file.name}', 'w', encoding='utf-8') as out:
+                        out.write('{expected}')
+                """)
+            interp.exec_sync(script)
+
+            file.seek(0)
+            content = file.read()
+            self.assertEqual(content, expected)
+
+    @unittest.skip('Fails on FreeBSD')
+    def test_already_running(self):
+        interp = interpreters.create()
+        with _running(interp):
+            with self.assertRaises(RuntimeError):
+                interp.exec_sync('print("spam")')
+
+    def test_bad_script(self):
+        interp = interpreters.create()
+        with self.assertRaises(TypeError):
+            interp.exec_sync(10)
+
+    def test_bytes_for_script(self):
+        interp = interpreters.create()
+        with self.assertRaises(TypeError):
+            interp.exec_sync(b'print("spam")')
+
+    def test_with_background_threads_still_running(self):
+        r_interp, w_interp = self.pipe()
+        r_thread, w_thread = self.pipe()
+
+        RAN = b'R'
+        DONE = b'D'
+        FINISHED = b'F'
+
+        interp = interpreters.create()
+        interp.exec_sync(f"""if True:
+            import os
+            import threading
+
+            def task():
+                v = os.read({r_thread}, 1)
+                assert v == {DONE!r}
+                os.write({w_interp}, {FINISHED!r})
+            t = threading.Thread(target=task)
+            t.start()
+            os.write({w_interp}, {RAN!r})
+            """)
+        interp.exec_sync(f"""if True:
+            os.write({w_interp}, {RAN!r})
+            """)
+
+        os.write(w_thread, DONE)
+        interp.exec_sync('t.join()')
+        self.assertEqual(os.read(r_interp, 1), RAN)
+        self.assertEqual(os.read(r_interp, 1), RAN)
+        self.assertEqual(os.read(r_interp, 1), FINISHED)
+
+    # test_xxsubinterpreters covers the remaining
+    # Interpreter.exec_sync() behavior.
+
+
+class TestInterpreterRun(TestBase):
+
+    def test_success(self):
+        interp = interpreters.create()
+        script, file = _captured_script('print("it worked!", end="")')
+        with file:
+            t = interp.run(script)
+            t.join()
+            out = file.read()
+
+        self.assertEqual(out, 'it worked!')
+
+    def test_failure(self):
+        caught = False
+        def excepthook(args):
+            nonlocal caught
+            caught = True
+        threading.excepthook = excepthook
+        try:
+            interp = interpreters.create()
+            t = interp.run('raise Exception')
+            t.join()
+
+            self.assertTrue(caught)
+        except BaseException:
+            threading.excepthook = threading.__excepthook__
+
+
+class TestIsShareable(TestBase):
+
+    def test_default_shareables(self):
+        shareables = [
+                # singletons
+                None,
+                # builtin objects
+                b'spam',
+                'spam',
+                10,
+                -10,
+                True,
+                False,
+                100.0,
+                (),
+                (1, ('spam', 'eggs'), True),
+                ]
+        for obj in shareables:
+            with self.subTest(obj):
+                shareable = interpreters.is_shareable(obj)
+                self.assertTrue(shareable)
+
+    def test_not_shareable(self):
+        class Cheese:
+            def __init__(self, name):
+                self.name = name
+            def __str__(self):
+                return self.name
+
+        class SubBytes(bytes):
+            """A subclass of a shareable type."""
+
+        not_shareables = [
+                # singletons
+                NotImplemented,
+                ...,
+                # builtin types and objects
+                type,
+                object,
+                object(),
+                Exception(),
+                # user-defined types and objects
+                Cheese,
+                Cheese('Wensleydale'),
+                SubBytes(b'spam'),
+                ]
+        for obj in not_shareables:
+            with self.subTest(repr(obj)):
+                self.assertFalse(
+                    interpreters.is_shareable(obj))
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

Lib/test/test_interpreters/test_channels.py

@@ -0,0 +1,328 @@
+import threading
+from textwrap import dedent
+import unittest
+import time
+
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+_channels = import_helper.import_module('_xxinterpchannels')
+from test.support import interpreters
+from test.support.interpreters import channels
+from .utils import _run_output, TestBase
+
+
+class TestChannels(TestBase):
+
+    def test_create(self):
+        r, s = channels.create()
+        self.assertIsInstance(r, channels.RecvChannel)
+        self.assertIsInstance(s, channels.SendChannel)
+
+    def test_list_all(self):
+        self.assertEqual(channels.list_all(), [])
+        created = set()
+        for _ in range(3):
+            ch = channels.create()
+            created.add(ch)
+        after = set(channels.list_all())
+        self.assertEqual(after, created)
+
+    def test_shareable(self):
+        rch, sch = channels.create()
+
+        self.assertTrue(
+            interpreters.is_shareable(rch))
+        self.assertTrue(
+            interpreters.is_shareable(sch))
+
+        sch.send_nowait(rch)
+        sch.send_nowait(sch)
+        rch2 = rch.recv()
+        sch2 = rch.recv()
+
+        self.assertEqual(rch2, rch)
+        self.assertEqual(sch2, sch)
+
+    def test_is_closed(self):
+        rch, sch = channels.create()
+        rbefore = rch.is_closed
+        sbefore = sch.is_closed
+        rch.close()
+        rafter = rch.is_closed
+        safter = sch.is_closed
+
+        self.assertFalse(rbefore)
+        self.assertFalse(sbefore)
+        self.assertTrue(rafter)
+        self.assertTrue(safter)
+
+
+class TestRecvChannelAttrs(TestBase):
+
+    def test_id_type(self):
+        rch, _ = channels.create()
+        self.assertIsInstance(rch.id, _channels.ChannelID)
+
+    def test_custom_id(self):
+        rch = channels.RecvChannel(1)
+        self.assertEqual(rch.id, 1)
+
+        with self.assertRaises(TypeError):
+            channels.RecvChannel('1')
+
+    def test_id_readonly(self):
+        rch = channels.RecvChannel(1)
+        with self.assertRaises(AttributeError):
+            rch.id = 2
+
+    def test_equality(self):
+        ch1, _ = channels.create()
+        ch2, _ = channels.create()
+        self.assertEqual(ch1, ch1)
+        self.assertNotEqual(ch1, ch2)
+
+
+class TestSendChannelAttrs(TestBase):
+
+    def test_id_type(self):
+        _, sch = channels.create()
+        self.assertIsInstance(sch.id, _channels.ChannelID)
+
+    def test_custom_id(self):
+        sch = channels.SendChannel(1)
+        self.assertEqual(sch.id, 1)
+
+        with self.assertRaises(TypeError):
+            channels.SendChannel('1')
+
+    def test_id_readonly(self):
+        sch = channels.SendChannel(1)
+        with self.assertRaises(AttributeError):
+            sch.id = 2
+
+    def test_equality(self):
+        _, ch1 = channels.create()
+        _, ch2 = channels.create()
+        self.assertEqual(ch1, ch1)
+        self.assertNotEqual(ch1, ch2)
+
+
+class TestSendRecv(TestBase):
+
+    def test_send_recv_main(self):
+        r, s = channels.create()
+        orig = b'spam'
+        s.send_nowait(orig)
+        obj = r.recv()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            from test.support.interpreters import channels
+            r, s = channels.create()
+            orig = b'spam'
+            s.send_nowait(orig)
+            obj = r.recv()
+            assert obj == orig, 'expected: obj == orig'
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.skip('broken (see BPO-...)')
+    def test_send_recv_different_interpreters(self):
+        r1, s1 = channels.create()
+        r2, s2 = channels.create()
+        orig1 = b'spam'
+        s1.send_nowait(orig1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                obj1 = r.recv()
+                assert obj1 == b'spam', 'expected: obj1 == orig1'
+                # When going to another interpreter we get a copy.
+                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
+                orig2 = b'eggs'
+                print(id(orig2))
+                s.send_nowait(orig2)
+                """),
+            channels=dict(r=r1, s=s2),
+            )
+        obj2 = r2.recv()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_send_recv_different_threads(self):
+        r, s = channels.create()
+
+        def f():
+            while True:
+                try:
+                    obj = r.recv()
+                    break
+                except channels.ChannelEmptyError:
+                    time.sleep(0.1)
+            s.send(obj)
+        t = threading.Thread(target=f)
+        t.start()
+
+        orig = b'spam'
+        s.send(orig)
+        obj = r.recv()
+        t.join()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_nowait_main(self):
+        r, s = channels.create()
+        orig = b'spam'
+        s.send_nowait(orig)
+        obj = r.recv_nowait()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+    def test_send_recv_nowait_main_with_default(self):
+        r, _ = channels.create()
+        obj = r.recv_nowait(None)
+
+        self.assertIsNone(obj)
+
+    def test_send_recv_nowait_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            from test.support.interpreters import channels
+            r, s = channels.create()
+            orig = b'spam'
+            s.send_nowait(orig)
+            obj = r.recv_nowait()
+            assert obj == orig, 'expected: obj == orig'
+            # When going back to the same interpreter we get the same object.
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.skip('broken (see BPO-...)')
+    def test_send_recv_nowait_different_interpreters(self):
+        r1, s1 = channels.create()
+        r2, s2 = channels.create()
+        orig1 = b'spam'
+        s1.send_nowait(orig1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                obj1 = r.recv_nowait()
+                assert obj1 == b'spam', 'expected: obj1 == orig1'
+                # When going to another interpreter we get a copy.
+                assert id(obj1) != {id(orig1)}, 'expected: obj1 is not orig1'
+                orig2 = b'eggs'
+                print(id(orig2))
+                s.send_nowait(orig2)
+                """),
+            channels=dict(r=r1, s=s2),
+            )
+        obj2 = r2.recv_nowait()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_recv_timeout(self):
+        r, _ = channels.create()
+        with self.assertRaises(TimeoutError):
+            r.recv(timeout=1)
+
+    def test_recv_channel_does_not_exist(self):
+        ch = channels.RecvChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.recv()
+
+    def test_send_channel_does_not_exist(self):
+        ch = channels.SendChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.send(b'spam')
+
+    def test_recv_nowait_channel_does_not_exist(self):
+        ch = channels.RecvChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.recv_nowait()
+
+    def test_send_nowait_channel_does_not_exist(self):
+        ch = channels.SendChannel(1_000_000)
+        with self.assertRaises(channels.ChannelNotFoundError):
+            ch.send_nowait(b'spam')
+
+    def test_recv_nowait_empty(self):
+        ch, _ = channels.create()
+        with self.assertRaises(channels.ChannelEmptyError):
+            ch.recv_nowait()
+
+    def test_recv_nowait_default(self):
+        default = object()
+        rch, sch = channels.create()
+        obj1 = rch.recv_nowait(default)
+        sch.send_nowait(None)
+        sch.send_nowait(1)
+        sch.send_nowait(b'spam')
+        sch.send_nowait(b'eggs')
+        obj2 = rch.recv_nowait(default)
+        obj3 = rch.recv_nowait(default)
+        obj4 = rch.recv_nowait()
+        obj5 = rch.recv_nowait(default)
+        obj6 = rch.recv_nowait(default)
+
+        self.assertIs(obj1, default)
+        self.assertIs(obj2, None)
+        self.assertEqual(obj3, 1)
+        self.assertEqual(obj4, b'spam')
+        self.assertEqual(obj5, b'eggs')
+        self.assertIs(obj6, default)
+
+    def test_send_buffer(self):
+        buf = bytearray(b'spamspamspam')
+        obj = None
+        rch, sch = channels.create()
+
+        def f():
+            nonlocal obj
+            while True:
+                try:
+                    obj = rch.recv()
+                    break
+                except channels.ChannelEmptyError:
+                    time.sleep(0.1)
+        t = threading.Thread(target=f)
+        t.start()
+
+        sch.send_buffer(buf)
+        t.join()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
+    def test_send_buffer_nowait(self):
+        buf = bytearray(b'spamspamspam')
+        rch, sch = channels.create()
+        sch.send_buffer_nowait(buf)
+        obj = rch.recv()
+
+        self.assertIsNot(obj, buf)
+        self.assertIsInstance(obj, memoryview)
+        self.assertEqual(obj, buf)
+
+        buf[4:8] = b'eggs'
+        self.assertEqual(obj, buf)
+        obj[4:8] = b'ham.'
+        self.assertEqual(obj, buf)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

Lib/test/test_interpreters/test_lifecycle.py

@@ -0,0 +1,189 @@
+import contextlib
+import json
+import os
+import os.path
+import sys
+from textwrap import dedent
+import unittest
+
+from test import support
+from test.support import import_helper
+from test.support import os_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from .utils import TestBase
+
+
+class StartupTests(TestBase):
+
+    # We want to ensure the initial state of subinterpreters
+    # matches expectations.
+
+    _subtest_count = 0
+
+    @contextlib.contextmanager
+    def subTest(self, *args):
+        with super().subTest(*args) as ctx:
+            self._subtest_count += 1
+            try:
+                yield ctx
+            finally:
+                if self._debugged_in_subtest:
+                    if self._subtest_count == 1:
+                        # The first subtest adds a leading newline, so we
+                        # compensate here by not printing a trailing newline.
+                        print('### end subtest debug ###', end='')
+                    else:
+                        print('### end subtest debug ###')
+                self._debugged_in_subtest = False
+
+    def debug(self, msg, *, header=None):
+        if header:
+            self._debug(f'--- {header} ---')
+            if msg:
+                if msg.endswith(os.linesep):
+                    self._debug(msg[:-len(os.linesep)])
+                else:
+                    self._debug(msg)
+                    self._debug('<no newline>')
+            self._debug('------')
+        else:
+            self._debug(msg)
+
+    _debugged = False
+    _debugged_in_subtest = False
+    def _debug(self, msg):
+        if not self._debugged:
+            print()
+            self._debugged = True
+        if self._subtest is not None:
+            if True:
+                if not self._debugged_in_subtest:
+                    self._debugged_in_subtest = True
+                    print('### start subtest debug ###')
+                print(msg)
+        else:
+            print(msg)
+
+    def create_temp_dir(self):
+        import tempfile
+        tmp = tempfile.mkdtemp(prefix='test_interpreters_')
+        tmp = os.path.realpath(tmp)
+        self.addCleanup(os_helper.rmtree, tmp)
+        return tmp
+
+    def write_script(self, *path, text):
+        filename = os.path.join(*path)
+        dirname = os.path.dirname(filename)
+        if dirname:
+            os.makedirs(dirname, exist_ok=True)
+        with open(filename, 'w', encoding='utf-8') as outfile:
+            outfile.write(dedent(text))
+        return filename
+
+    @support.requires_subprocess()
+    def run_python(self, argv, *, cwd=None):
+        # This method is inspired by
+        # EmbeddingTestsMixin.run_embedded_interpreter() in test_embed.py.
+        import shlex
+        import subprocess
+        if isinstance(argv, str):
+            argv = shlex.split(argv)
+        argv = [sys.executable, *argv]
+        try:
+            proc = subprocess.run(
+                argv,
+                cwd=cwd,
+                capture_output=True,
+                text=True,
+            )
+        except Exception as exc:
+            self.debug(f'# cmd: {shlex.join(argv)}')
+            if isinstance(exc, FileNotFoundError) and not exc.filename:
+                if os.path.exists(argv[0]):
+                    exists = 'exists'
+                else:
+                    exists = 'does not exist'
+                self.debug(f'{argv[0]} {exists}')
+            raise  # re-raise
+        assert proc.stderr == '' or proc.returncode != 0, proc.stderr
+        if proc.returncode != 0 and support.verbose:
+            self.debug(f'# python3 {shlex.join(argv[1:])} failed:')
+            self.debug(proc.stdout, header='stdout')
+            self.debug(proc.stderr, header='stderr')
+        self.assertEqual(proc.returncode, 0)
+        self.assertEqual(proc.stderr, '')
+        return proc.stdout
+
+    def test_sys_path_0(self):
+        # The main interpreter's sys.path[0] should be used by subinterpreters.
+        script = '''
+            import sys
+            from test.support import interpreters
+
+            orig = sys.path[0]
+
+            interp = interpreters.create()
+            interp.exec_sync(f"""if True:
+                import json
+                import sys
+                print(json.dumps({{
+                    'main': {orig!r},
+                    'sub': sys.path[0],
+                }}, indent=4), flush=True)
+                """)
+            '''
+        # <tmp>/
+        #   pkg/
+        #     __init__.py
+        #     __main__.py
+        #     script.py
+        #   script.py
+        cwd = self.create_temp_dir()
+        self.write_script(cwd, 'pkg', '__init__.py', text='')
+        self.write_script(cwd, 'pkg', '__main__.py', text=script)
+        self.write_script(cwd, 'pkg', 'script.py', text=script)
+        self.write_script(cwd, 'script.py', text=script)
+
+        cases = [
+            ('script.py', cwd),
+            ('-m script', cwd),
+            ('-m pkg', cwd),
+            ('-m pkg.script', cwd),
+            ('-c "import script"', ''),
+        ]
+        for argv, expected in cases:
+            with self.subTest(f'python3 {argv}'):
+                out = self.run_python(argv, cwd=cwd)
+                data = json.loads(out)
+                sp0_main, sp0_sub = data['main'], data['sub']
+                self.assertEqual(sp0_sub, sp0_main)
+                self.assertEqual(sp0_sub, expected)
+        # XXX Also check them all with the -P cmdline flag?
+
+
+class FinalizationTests(TestBase):
+
+    def test_gh_109793(self):
+        # Make sure finalization finishes and the correct error code
+        # is reported, even when subinterpreters get cleaned up at the end.
+        import subprocess
+        argv = [sys.executable, '-c', '''if True:
+            from test.support import interpreters
+            interp = interpreters.create()
+            raise Exception
+            ''']
+        proc = subprocess.run(argv, capture_output=True, text=True)
+        self.assertIn('Traceback', proc.stderr)
+        if proc.returncode == 0 and support.verbose:
+            print()
+            print("--- cmd unexpected succeeded ---")
+            print(f"stdout:\n{proc.stdout}")
+            print(f"stderr:\n{proc.stderr}")
+            print("------")
+        self.assertEqual(proc.returncode, 1)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

Lib/test/test_interpreters/test_queues.py

@@ -0,0 +1,233 @@
+import threading
+from textwrap import dedent
+import unittest
+import time
+
+from test.support import import_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxinterpchannels')
+#import_helper.import_module('_xxinterpqueues')
+from test.support import interpreters
+from test.support.interpreters import queues
+from .utils import _run_output, TestBase
+
+
+class QueueTests(TestBase):
+
+    def test_create(self):
+        with self.subTest('vanilla'):
+            queue = queues.create()
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('small maxsize'):
+            queue = queues.create(3)
+            self.assertEqual(queue.maxsize, 3)
+
+        with self.subTest('big maxsize'):
+            queue = queues.create(100)
+            self.assertEqual(queue.maxsize, 100)
+
+        with self.subTest('no maxsize'):
+            queue = queues.create(0)
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('negative maxsize'):
+            queue = queues.create(-1)
+            self.assertEqual(queue.maxsize, 0)
+
+        with self.subTest('bad maxsize'):
+            with self.assertRaises(TypeError):
+                queues.create('1')
+
+    @unittest.expectedFailure
+    def test_shareable(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        queue1.put(queue2)
+        queue3 = queue1.get()
+        self.assertIs(queue3, queue1)
+
+    def test_id_type(self):
+        queue = queues.create()
+        self.assertIsInstance(queue.id, int)
+
+    def test_custom_id(self):
+        with self.assertRaises(queues.QueueNotFoundError):
+            queues.Queue(1_000_000)
+
+    def test_id_readonly(self):
+        queue = queues.create()
+        with self.assertRaises(AttributeError):
+            queue.id = 1_000_000
+
+    def test_maxsize_readonly(self):
+        queue = queues.create(10)
+        with self.assertRaises(AttributeError):
+            queue.maxsize = 1_000_000
+
+    def test_hashable(self):
+        queue = queues.create()
+        expected = hash(queue.id)
+        actual = hash(queue)
+        self.assertEqual(actual, expected)
+
+    def test_equality(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        self.assertEqual(queue1, queue1)
+        self.assertNotEqual(queue1, queue2)
+
+
+class TestQueueOps(TestBase):
+
+    def test_empty(self):
+        queue = queues.create()
+        before = queue.empty()
+        queue.put(None)
+        during = queue.empty()
+        queue.get()
+        after = queue.empty()
+
+        self.assertIs(before, True)
+        self.assertIs(during, False)
+        self.assertIs(after, True)
+
+    def test_full(self):
+        expected = [False, False, False, True, False, False, False]
+        actual = []
+        queue = queues.create(3)
+        for _ in range(3):
+            actual.append(queue.full())
+            queue.put(None)
+        actual.append(queue.full())
+        for _ in range(3):
+            queue.get()
+            actual.append(queue.full())
+
+        self.assertEqual(actual, expected)
+
+    def test_qsize(self):
+        expected = [0, 1, 2, 3, 2, 3, 2, 1, 0, 1, 0]
+        actual = []
+        queue = queues.create()
+        for _ in range(3):
+            actual.append(queue.qsize())
+            queue.put(None)
+        actual.append(queue.qsize())
+        queue.get()
+        actual.append(queue.qsize())
+        queue.put(None)
+        actual.append(queue.qsize())
+        for _ in range(3):
+            queue.get()
+            actual.append(queue.qsize())
+        queue.put(None)
+        actual.append(queue.qsize())
+        queue.get()
+        actual.append(queue.qsize())
+
+        self.assertEqual(actual, expected)
+
+    def test_put_get_main(self):
+        expected = list(range(20))
+        queue = queues.create()
+        for i in range(20):
+            queue.put(i)
+        actual = [queue.get() for _ in range(20)]
+
+        self.assertEqual(actual, expected)
+
+    @unittest.expectedFailure
+    def test_put_timeout(self):
+        queue = queues.create(2)
+        queue.put(None)
+        queue.put(None)
+        with self.assertRaises(queues.QueueFull):
+            queue.put(None, timeout=0.1)
+        queue.get()
+        queue.put(None)
+
+    @unittest.expectedFailure
+    def test_put_nowait(self):
+        queue = queues.create(2)
+        queue.put_nowait(None)
+        queue.put_nowait(None)
+        with self.assertRaises(queues.QueueFull):
+            queue.put_nowait(None)
+        queue.get()
+        queue.put_nowait(None)
+
+    def test_get_timeout(self):
+        queue = queues.create()
+        with self.assertRaises(queues.QueueEmpty):
+            queue.get(timeout=0.1)
+
+    def test_get_nowait(self):
+        queue = queues.create()
+        with self.assertRaises(queues.QueueEmpty):
+            queue.get_nowait()
+
+    def test_put_get_same_interpreter(self):
+        interp = interpreters.create()
+        interp.exec_sync(dedent("""
+            from test.support.interpreters import queues
+            queue = queues.create()
+            orig = b'spam'
+            queue.put(orig)
+            obj = queue.get()
+            assert obj == orig, 'expected: obj == orig'
+            assert obj is not orig, 'expected: obj is not orig'
+            """))
+
+    @unittest.expectedFailure
+    def test_put_get_different_interpreters(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+        obj1 = b'spam'
+        queue1.put(obj1)
+        out = _run_output(
+            interpreters.create(),
+            dedent(f"""
+                import test.support.interpreters.queue as queues
+                queue1 = queues.Queue({queue1.id})
+                queue2 = queues.Queue({queue2.id})
+                obj = queue1.get()
+                assert obj == b'spam', 'expected: obj == obj1'
+                # When going to another interpreter we get a copy.
+                assert id(obj) != {id(obj1)}, 'expected: obj is not obj1'
+                obj2 = b'eggs'
+                print(id(obj2))
+                queue2.put(obj2)
+                """))
+        obj2 = queue2.get()
+
+        self.assertEqual(obj2, b'eggs')
+        self.assertNotEqual(id(obj2), int(out))
+
+    def test_put_get_different_threads(self):
+        queue1 = queues.create()
+        queue2 = queues.create()
+
+        def f():
+            while True:
+                try:
+                    obj = queue1.get(timeout=0.1)
+                    break
+                except queues.QueueEmpty:
+                    continue
+            queue2.put(obj)
+        t = threading.Thread(target=f)
+        t.start()
+
+        orig = b'spam'
+        queue1.put(orig)
+        obj = queue2.get()
+        t.join()
+
+        self.assertEqual(obj, orig)
+        self.assertIsNot(obj, orig)
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

Lib/test/test_interpreters/test_stress.py

@@ -0,0 +1,38 @@
+import threading
+import unittest
+
+from test import support
+from test.support import import_helper
+from test.support import threading_helper
+# Raise SkipTest if subinterpreters not supported.
+import_helper.import_module('_xxsubinterpreters')
+from test.support import interpreters
+from .utils import TestBase
+
+
+class StressTests(TestBase):
+
+    # In these tests we generally want a lot of interpreters,
+    # but not so many that any test takes too long.
+
+    @support.requires_resource('cpu')
+    def test_create_many_sequential(self):
+        alive = []
+        for _ in range(100):
+            interp = interpreters.create()
+            alive.append(interp)
+
+    @support.requires_resource('cpu')
+    def test_create_many_threaded(self):
+        alive = []
+        def task():
+            interp = interpreters.create()
+            alive.append(interp)
+        threads = (threading.Thread(target=task) for _ in range(200))
+        with threading_helper.start_threads(threads):
+            pass
+
+
+if __name__ == '__main__':
+    # Test needs to be a package, so we can do relative imports.
+    unittest.main()

Lib/test/test_interpreters/utils.py

@@ -0,0 +1,73 @@
+import contextlib
+import os
+import threading
+from textwrap import dedent
+import unittest
+
+from test.support import interpreters
+
+
+def _captured_script(script):
+    r, w = os.pipe()
+    indented = script.replace('\n', '\n                ')
+    wrapped = dedent(f"""
+        import contextlib
+        with open({w}, 'w', encoding='utf-8') as spipe:
+            with contextlib.redirect_stdout(spipe):
+                {indented}
+        """)
+    return wrapped, open(r, encoding='utf-8')
+
+
+def clean_up_interpreters():
+    for interp in interpreters.list_all():
+        if interp.id == 0:  # main
+            continue
+        try:
+            interp.close()
+        except RuntimeError:
+            pass  # already destroyed
+
+
+def _run_output(interp, request, channels=None):
+    script, rpipe = _captured_script(request)
+    with rpipe:
+        interp.exec_sync(script, channels=channels)
+        return rpipe.read()
+
+
+@contextlib.contextmanager
+def _running(interp):
+    r, w = os.pipe()
+    def run():
+        interp.exec_sync(dedent(f"""
+            # wait for "signal"
+            with open({r}) as rpipe:
+                rpipe.read()
+            """))
+
+    t = threading.Thread(target=run)
+    t.start()
+
+    yield
+
+    with open(w, 'w') as spipe:
+        spipe.write('done')
+    t.join()
+
+
+class TestBase(unittest.TestCase):
+
+    def pipe(self):
+        def ensure_closed(fd):
+            try:
+                os.close(fd)
+            except OSError:
+                pass
+        r, w = os.pipe()
+        self.addCleanup(lambda: ensure_closed(r))
+        self.addCleanup(lambda: ensure_closed(w))
+        return r, w
+
+    def tearDown(self):
+        clean_up_interpreters()

Lib/test/test_sys.py

@@ -729,7 +729,7 @@ class SysModuleTest(unittest.TestCase):
         self.assertIs(t, s)
 
         interp = interpreters.create()
-        interp.run(textwrap.dedent(f'''
+        interp.exec_sync(textwrap.dedent(f'''
             import sys
             t = sys.intern({s!r})
             assert id(t) != {id(s)}, (id(t), {id(s)})
@@ -744,7 +744,7 @@ class SysModuleTest(unittest.TestCase):
         t = sys.intern(s)
 
         interp = interpreters.create()
-        interp.run(textwrap.dedent(f'''
+        interp.exec_sync(textwrap.dedent(f'''
             import sys
             t = sys.intern({s!r})
             assert id(t) == {id(t)}, (id(t), {id(t)})

Lib/test/test_threading.py

@@ -1365,7 +1365,7 @@ class SubinterpThreadingTests(BaseTestCase):
         DONE = b'D'
 
         interp = interpreters.create()
-        interp.run(f"""if True:
+        interp.exec_sync(f"""if True:
             import os
             import threading
             import time

Modules/_testcapimodule.c

@@ -13,6 +13,7 @@
 #include "_testcapi/parts.h"
 
 #include "frameobject.h"          // PyFrame_New()
+#include "interpreteridobject.h"  // PyInterpreterID_Type
 #include "marshal.h"              // PyMarshal_WriteLongToFile()
 
 #include <float.h>                // FLT_MAX
@@ -1451,6 +1452,36 @@ run_in_subinterp(PyObject *self, PyObject *args)
     return PyLong_FromLong(r);
 }
 
+static PyObject *
+get_interpreterid_type(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return Py_NewRef(&PyInterpreterID_Type);
+}
+
+static PyObject *
+link_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        assert(PyErr_Occurred());
+        return NULL;
+    }
+    _PyInterpreterState_RequireIDRef(interp, 1);
+    Py_RETURN_NONE;
+}
+
+static PyObject *
+unlink_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        assert(PyErr_Occurred());
+        return NULL;
+    }
+    _PyInterpreterState_RequireIDRef(interp, 0);
+    Py_RETURN_NONE;
+}
+
 static PyMethodDef ml;
 
 static PyObject *
@@ -3237,6 +3268,9 @@ static PyMethodDef TestMethods[] = {
     {"crash_no_current_thread", crash_no_current_thread,         METH_NOARGS},
     {"test_current_tstate_matches", test_current_tstate_matches, METH_NOARGS},
     {"run_in_subinterp",        run_in_subinterp,                METH_VARARGS},
+    {"get_interpreterid_type",  get_interpreterid_type,          METH_NOARGS},
+    {"link_interpreter_refcount", link_interpreter_refcount,     METH_O},
+    {"unlink_interpreter_refcount", unlink_interpreter_refcount, METH_O},
     {"create_cfunction",        create_cfunction,                METH_NOARGS},
     {"call_in_temporary_c_thread", call_in_temporary_c_thread, METH_VARARGS,
      PyDoc_STR("set_error_class(error_class) -> None")},

Modules/_testinternalcapi.c

@@ -1475,6 +1475,17 @@ run_in_subinterp_with_config(PyObject *self, PyObject *args, PyObject *kwargs)
 }
 
 
+static PyObject *
+get_interpreter_refcount(PyObject *self, PyObject *idobj)
+{
+    PyInterpreterState *interp = PyInterpreterID_LookUp(idobj);
+    if (interp == NULL) {
+        return NULL;
+    }
+    return PyLong_FromLongLong(interp->id_refcount);
+}
+
+
 static void
 _xid_capsule_destructor(PyObject *capsule)
 {
@@ -1693,6 +1704,7 @@ static PyMethodDef module_functions[] = {
     {"run_in_subinterp_with_config",
      _PyCFunction_CAST(run_in_subinterp_with_config),
      METH_VARARGS | METH_KEYWORDS},
+    {"get_interpreter_refcount", get_interpreter_refcount, METH_O},
     {"compile_perf_trampoline_entry", compile_perf_trampoline_entry, METH_VARARGS},
     {"perf_trampoline_set_persist_after_fork", perf_trampoline_set_persist_after_fork, METH_VARARGS},
     {"get_crossinterp_data",    get_crossinterp_data,            METH_VARARGS},

Modules/_xxinterpchannelsmodule.c

@@ -8,7 +8,6 @@
 #include "Python.h"
 #include "interpreteridobject.h"
 #include "pycore_crossinterp.h"   // struct _xid
-#include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
 #include "pycore_interp.h"        // _PyInterpreterState_LookUpID()
 
 #ifdef MS_WINDOWS
@@ -263,136 +262,6 @@ wait_for_lock(PyThread_type_lock mutex, PY_TIMEOUT_T timeout)
 }
 
 
-/* Cross-interpreter Buffer Views *******************************************/
-
-// XXX Release when the original interpreter is destroyed.
-
-typedef struct {
-    PyObject_HEAD
-    Py_buffer *view;
-    int64_t interpid;
-} XIBufferViewObject;
-
-static PyObject *
-xibufferview_from_xid(PyTypeObject *cls, _PyCrossInterpreterData *data)
-{
-    assert(data->data != NULL);
-    assert(data->obj == NULL);
-    assert(data->interpid >= 0);
-    XIBufferViewObject *self = PyObject_Malloc(sizeof(XIBufferViewObject));
-    if (self == NULL) {
-        return NULL;
-    }
-    PyObject_Init((PyObject *)self, cls);
-    self->view = (Py_buffer *)data->data;
-    self->interpid = data->interpid;
-    return (PyObject *)self;
-}
-
-static void
-xibufferview_dealloc(XIBufferViewObject *self)
-{
-    PyInterpreterState *interp = _PyInterpreterState_LookUpID(self->interpid);
-    /* If the interpreter is no longer alive then we have problems,
-       since other objects may be using the buffer still. */
-    assert(interp != NULL);
-
-    if (_PyBuffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
-        // XXX Emit a warning?
-        PyErr_Clear();
-    }
-
-    PyTypeObject *tp = Py_TYPE(self);
-    tp->tp_free(self);
-    /* "Instances of heap-allocated types hold a reference to their type."
-     * See: https://docs.python.org/3.11/howto/isolating-extensions.html#garbage-collection-protocol
-     * See: https://docs.python.org/3.11/c-api/typeobj.html#c.PyTypeObject.tp_traverse
-    */
-    // XXX Why don't we implement Py_TPFLAGS_HAVE_GC, e.g. Py_tp_traverse,
-    // like we do for _abc._abc_data?
-    Py_DECREF(tp);
-}
-
-static int
-xibufferview_getbuf(XIBufferViewObject *self, Py_buffer *view, int flags)
-{
-    /* Only PyMemoryView_FromObject() should ever call this,
-       via _memoryview_from_xid() below. */
-    *view = *self->view;
-    view->obj = (PyObject *)self;
-    // XXX Should we leave it alone?
-    view->internal = NULL;
-    return 0;
-}
-
-static PyType_Slot XIBufferViewType_slots[] = {
-    {Py_tp_dealloc, (destructor)xibufferview_dealloc},
-    {Py_bf_getbuffer, (getbufferproc)xibufferview_getbuf},
-    // We don't bother with Py_bf_releasebuffer since we don't need it.
-    {0, NULL},
-};
-
-static PyType_Spec XIBufferViewType_spec = {
-    .name = MODULE_NAME ".CrossInterpreterBufferView",
-    .basicsize = sizeof(XIBufferViewObject),
-    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
-              Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE),
-    .slots = XIBufferViewType_slots,
-};
-
-
-/* extra XID types **********************************************************/
-
-static PyTypeObject * _get_current_xibufferview_type(void);
-
-static PyObject *
-_memoryview_from_xid(_PyCrossInterpreterData *data)
-{
-    PyTypeObject *cls = _get_current_xibufferview_type();
-    if (cls == NULL) {
-        return NULL;
-    }
-    PyObject *obj = xibufferview_from_xid(cls, data);
-    if (obj == NULL) {
-        return NULL;
-    }
-    return PyMemoryView_FromObject(obj);
-}
-
-static int
-_memoryview_shared(PyThreadState *tstate, PyObject *obj,
-                   _PyCrossInterpreterData *data)
-{
-    Py_buffer *view = PyMem_RawMalloc(sizeof(Py_buffer));
-    if (view == NULL) {
-        return -1;
-    }
-    if (PyObject_GetBuffer(obj, view, PyBUF_FULL_RO) < 0) {
-        PyMem_RawFree(view);
-        return -1;
-    }
-    _PyCrossInterpreterData_Init(data, tstate->interp, view, NULL,
-                                 _memoryview_from_xid);
-    return 0;
-}
-
-static int
-register_builtin_xid_types(struct xid_class_registry *classes)
-{
-    PyTypeObject *cls;
-    crossinterpdatafunc func;
-
-    // builtin memoryview
-    cls = &PyMemoryView_Type;
-    func = _memoryview_shared;
-    if (register_xid_class(cls, func, classes)) {
-        return -1;
-    }
-
-    return 0;
-}
-
-
 /* module state *************************************************************/
 
 typedef struct {
@@ -405,7 +274,6 @@ typedef struct {
     /* heap types */
     PyTypeObject *ChannelInfoType;
     PyTypeObject *ChannelIDType;
-    PyTypeObject *XIBufferViewType;
 
     /* exceptions */
     PyObject *ChannelError;
@@ -449,7 +317,6 @@ traverse_module_state(module_state *state, visitproc visit, void *arg)
     /* heap types */
     Py_VISIT(state->ChannelInfoType);
     Py_VISIT(state->ChannelIDType);
-    Py_VISIT(state->XIBufferViewType);
 
     /* exceptions */
     Py_VISIT(state->ChannelError);
@@ -474,7 +341,6 @@ clear_module_state(module_state *state)
         (void)_PyCrossInterpreterData_UnregisterClass(state->ChannelIDType);
     }
     Py_CLEAR(state->ChannelIDType);
-    Py_CLEAR(state->XIBufferViewType);
 
     /* exceptions */
     Py_CLEAR(state->ChannelError);
@@ -487,17 +353,6 @@ clear_module_state(module_state *state)
 }
 
 
-static PyTypeObject *
-_get_current_xibufferview_type(void)
-{
-    module_state *state = _get_current_module_state();
-    if (state == NULL) {
-        return NULL;
-    }
-    return state->XIBufferViewType;
-}
-
-
 /* channel-specific code ****************************************************/
 
 #define CHANNEL_SEND 1
@@ -3463,18 +3318,6 @@ module_exec(PyObject *mod)
         goto error;
     }
 
-    // XIBufferView
-    state->XIBufferViewType = add_new_type(mod, &XIBufferViewType_spec, NULL,
-                                           xid_classes);
-    if (state->XIBufferViewType == NULL) {
-        goto error;
-    }
-
-    // Register external types.
-    if (register_builtin_xid_types(xid_classes) < 0) {
-        goto error;
-    }
-
     /* Make sure chnnels drop objects owned by this interpreter. */
     PyInterpreterState *interp = _get_current_interp();
     PyUnstable_AtExit(interp, clear_interpreter, (void *)interp);

Modules/_xxsubinterpretersmodule.c

@@ -6,11 +6,14 @@
 #endif
 
 #include "Python.h"
+#include "pycore_abstract.h"      // _PyIndex_Check()
 #include "pycore_crossinterp.h"   // struct _xid
-#include "pycore_pyerrors.h"      // _Py_excinfo
+#include "pycore_interp.h"        // _PyInterpreterState_IDIncref()
 #include "pycore_initconfig.h"    // _PyErr_SetFromPyStatus()
+#include "pycore_long.h"          // _PyLong_IsNegative()
 #include "pycore_modsupport.h"    // _PyArg_BadArgument()
-#include "pycore_pyerrors.h"      // _PyErr_ChainExceptions1()
+#include "pycore_pybuffer.h"      // _PyBuffer_ReleaseInInterpreterAndRawFree()
+#include "pycore_pyerrors.h"      // _Py_excinfo
 #include "pycore_pystate.h"       // _PyInterpreterState_SetRunningMain()
 
 #include "interpreteridobject.h"
@@ -28,11 +31,260 @@ _get_current_interp(void)
     return PyInterpreterState_Get();
 }
 
+static int64_t
+pylong_to_interpid(PyObject *idobj)
+{
+    assert(PyLong_CheckExact(idobj));
+
+    if (_PyLong_IsNegative((PyLongObject *)idobj)) {
+        PyErr_Format(PyExc_ValueError,
+                     "interpreter ID must be a non-negative int, got %R",
+                     idobj);
+        return -1;
+    }
+
+    int overflow;
+    long long id = PyLong_AsLongLongAndOverflow(idobj, &overflow);
+    if (id == -1) {
+        if (!overflow) {
+            assert(PyErr_Occurred());
+            return -1;
+        }
+        assert(!PyErr_Occurred());
+        // For now, we don't worry about if LLONG_MAX < INT64_MAX.
+        goto bad_id;
+    }
+#if LLONG_MAX > INT64_MAX
+    if (id > INT64_MAX) {
+        goto bad_id;
+    }
+#endif
+    return (int64_t)id;
+
+bad_id:
+    PyErr_Format(PyExc_RuntimeError,
+                 "unrecognized interpreter ID %O", idobj);
+    return -1;
+}
+
+static int64_t
+convert_interpid_obj(PyObject *arg)
+{
+    int64_t id = -1;
+    if (_PyIndex_Check(arg)) {
+        PyObject *idobj = PyNumber_Long(arg);
+        if (idobj == NULL) {
+            return -1;
+        }
+        id = pylong_to_interpid(idobj);
+        Py_DECREF(idobj);
+        if (id < 0) {
+            return -1;
+        }
+    }
+    else {
+        PyErr_Format(PyExc_TypeError,
+                     "interpreter ID must be an int, got %.100s",
+                     Py_TYPE(arg)->tp_name);
+        return -1;
+    }
+    return id;
+}
+
+static PyInterpreterState *
+look_up_interp(PyObject *arg)
+{
+    int64_t id = convert_interpid_obj(arg);
+    if (id < 0) {
+        return NULL;
+    }
+    return _PyInterpreterState_LookUpID(id);
+}
+
+
+static PyObject *
+interpid_to_pylong(int64_t id)
+{
+    assert(id < LLONG_MAX);
+    return PyLong_FromLongLong(id);
+}
+
+static PyObject *
+get_interpid_obj(PyInterpreterState *interp)
+{
+    if (_PyInterpreterState_IDInitref(interp) != 0) {
+        return NULL;
+    };
+    int64_t id = PyInterpreterState_GetID(interp);
+    if (id < 0) {
+        return NULL;
+    }
+    return interpid_to_pylong(id);
+}
+
+static PyObject *
+_get_current_module(void)
+{
+    PyObject *name = PyUnicode_FromString(MODULE_NAME);
+    if (name == NULL) {
+        return NULL;
+    }
+    PyObject *mod = PyImport_GetModule(name);
+    Py_DECREF(name);
+    if (mod == NULL) {
+        return NULL;
+    }
+    assert(mod != Py_None);
+    return mod;
+}
+
+
+/* Cross-interpreter Buffer Views *******************************************/
+
+// XXX Release when the original interpreter is destroyed.
+
+typedef struct {
+    PyObject_HEAD
+    Py_buffer *view;
+    int64_t interpid;
+} XIBufferViewObject;
+
+static PyObject *
+xibufferview_from_xid(PyTypeObject *cls, _PyCrossInterpreterData *data)
+{
+    assert(data->data != NULL);
+    assert(data->obj == NULL);
+    assert(data->interpid >= 0);
+    XIBufferViewObject *self = PyObject_Malloc(sizeof(XIBufferViewObject));
+    if (self == NULL) {
+        return NULL;
+    }
+    PyObject_Init((PyObject *)self, cls);
+    self->view = (Py_buffer *)data->data;
+    self->interpid = data->interpid;
+    return (PyObject *)self;
+}
+
+static void
+xibufferview_dealloc(XIBufferViewObject *self)
+{
+    PyInterpreterState *interp = _PyInterpreterState_LookUpID(self->interpid);
+    /* If the interpreter is no longer alive then we have problems,
+       since other objects may be using the buffer still. */
+    assert(interp != NULL);
+
+    if (_PyBuffer_ReleaseInInterpreterAndRawFree(interp, self->view) < 0) {
+        // XXX Emit a warning?
+        PyErr_Clear();
+    }
+
+    PyTypeObject *tp = Py_TYPE(self);
+    tp->tp_free(self);
+    /* "Instances of heap-allocated types hold a reference to their type."
+     * See: https://docs.python.org/3.11/howto/isolating-extensions.html#garbage-collection-protocol
+     * See: https://docs.python.org/3.11/c-api/typeobj.html#c.PyTypeObject.tp_traverse
+    */
+    // XXX Why don't we implement Py_TPFLAGS_HAVE_GC, e.g. Py_tp_traverse,
+    // like we do for _abc._abc_data?
+    Py_DECREF(tp);
+}
+
+static int
+xibufferview_getbuf(XIBufferViewObject *self, Py_buffer *view, int flags)
+{
+    /* Only PyMemoryView_FromObject() should ever call this,
+       via _memoryview_from_xid() below. */
+    *view = *self->view;
+    view->obj = (PyObject *)self;
+    // XXX Should we leave it alone?
+    view->internal = NULL;
+    return 0;
+}
+
+static PyType_Slot XIBufferViewType_slots[] = {
+    {Py_tp_dealloc, (destructor)xibufferview_dealloc},
+    {Py_bf_getbuffer, (getbufferproc)xibufferview_getbuf},
+    // We don't bother with Py_bf_releasebuffer since we don't need it.
+    {0, NULL},
+};
+
+static PyType_Spec XIBufferViewType_spec = {
+    .name = MODULE_NAME ".CrossInterpreterBufferView",
+    .basicsize = sizeof(XIBufferViewObject),
+    .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
+              Py_TPFLAGS_DISALLOW_INSTANTIATION | Py_TPFLAGS_IMMUTABLETYPE),
+    .slots = XIBufferViewType_slots,
+};
+
+
+static PyTypeObject * _get_current_xibufferview_type(void);
+
+static PyObject *
+_memoryview_from_xid(_PyCrossInterpreterData *data)
+{
+    PyTypeObject *cls = _get_current_xibufferview_type();
+    if (cls == NULL) {
+        return NULL;
+    }
+    PyObject *obj = xibufferview_from_xid(cls, data);
+    if (obj == NULL) {
+        return NULL;
+    }
+    return PyMemoryView_FromObject(obj);
+}
+
+static int
+_memoryview_shared(PyThreadState *tstate, PyObject *obj,
+                   _PyCrossInterpreterData *data)
+{
+    Py_buffer *view = PyMem_RawMalloc(sizeof(Py_buffer));
+    if (view == NULL) {
+        return -1;
+    }
+    if (PyObject_GetBuffer(obj, view, PyBUF_FULL_RO) < 0) {
+        PyMem_RawFree(view);
+        return -1;
+    }
+    _PyCrossInterpreterData_Init(data, tstate->interp, view, NULL,
+                                 _memoryview_from_xid);
+    return 0;
+}
+
+static int
+register_memoryview_xid(PyObject *mod, PyTypeObject **p_state)
+{
+    // XIBufferView
+    assert(*p_state == NULL);
+    PyTypeObject *cls = (PyTypeObject *)PyType_FromModuleAndSpec(
+                mod, &XIBufferViewType_spec, NULL);
+    if (cls == NULL) {
+        return -1;
+    }
+    if (PyModule_AddType(mod, cls) < 0) {
+        Py_DECREF(cls);
+        return -1;
+    }
+    *p_state = cls;
+
+    // Register XID for the builtin memoryview type.
+    if (_PyCrossInterpreterData_RegisterClass(
+                &PyMemoryView_Type, _memoryview_shared) < 0) {
+        return -1;
+    }
+    // We don't ever bother un-registering memoryview.
+
+    return 0;
+}
+
+
 
 /* module state *************************************************************/
 
 typedef struct {
     int _notused;
+
+    /* heap types */
+    PyTypeObject *XIBufferViewType;
 } module_state;
 
 static inline module_state *
@@ -44,19 +296,51 @@ get_module_state(PyObject *mod)
     return state;
 }
 
+static module_state *
+_get_current_module_state(void)
+{
+    PyObject *mod = _get_current_module();
+    if (mod == NULL) {
+        // XXX import it?
+        PyErr_SetString(PyExc_RuntimeError,
+                        MODULE_NAME " module not imported yet");
+        return NULL;
+    }
+    module_state *state = get_module_state(mod);
+    Py_DECREF(mod);
+    return state;
+}
+
 static int
 traverse_module_state(module_state *state, visitproc visit, void *arg)
 {
+    /* heap types */
+    Py_VISIT(state->XIBufferViewType);
+
     return 0;
 }
 
 static int
 clear_module_state(module_state *state)
 {
+    /* heap types */
+    Py_CLEAR(state->XIBufferViewType);
+
     return 0;
 }
 
 
+static PyTypeObject *
+_get_current_xibufferview_type(void)
+{
+    module_state *state = _get_current_module_state();
+    if (state == NULL) {
+        return NULL;
+    }
+    return state->XIBufferViewType;
+}
+
+
 /* Python code **************************************************************/
 
 static const char *
@@ -254,7 +538,7 @@ interp_create(PyObject *self, PyObject *args, PyObject *kwds)
     assert(tstate != NULL);
 
     PyInterpreterState *interp = PyThreadState_GetInterpreter(tstate);
-    PyObject *idobj = PyInterpreterState_GetIDObject(interp);
+    PyObject *idobj = get_interpid_obj(interp);
     if (idobj == NULL) {
         // XXX Possible GILState issues?
         save_tstate = PyThreadState_Swap(tstate);
@@ -273,7 +557,9 @@ interp_create(PyObject *self, PyObject *args, PyObject *kwds)
 PyDoc_STRVAR(create_doc,
 "create() -> ID\n\
 \n\
-Create a new interpreter and return a unique generated ID.");
+Create a new interpreter and return a unique generated ID.\n\
+\n\
+The caller is responsible for destroying the interpreter before exiting.");
 
 
 static PyObject *
@@ -288,7 +574,7 @@ interp_destroy(PyObject *self, PyObject *args, PyObject *kwds)
     }
 
     // Look up the interpreter.
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id);
+    PyInterpreterState *interp = look_up_interp(id);
     if (interp == NULL) {
         return NULL;
     }
@@ -345,7 +631,7 @@ interp_list_all(PyObject *self, PyObject *Py_UNUSED(ignored))
 
     interp = PyInterpreterState_Head();
     while (interp != NULL) {
-        id = PyInterpreterState_GetIDObject(interp);
+        id = get_interpid_obj(interp);
         if (id == NULL) {
             Py_DECREF(ids);
             return NULL;
@@ -377,7 +663,7 @@ interp_get_current(PyObject *self, PyObject *Py_UNUSED(ignored))
     if (interp == NULL) {
         return NULL;
     }
-    return PyInterpreterState_GetIDObject(interp);
+    return get_interpid_obj(interp);
 }
 
 PyDoc_STRVAR(get_current_doc,
@@ -391,7 +677,7 @@ interp_get_main(PyObject *self, PyObject *Py_UNUSED(ignored))
 {
     // Currently, 0 is always the main interpreter.
     int64_t id = 0;
-    return PyInterpreterID_New(id);
+    return PyLong_FromLongLong(id);
 }
 
 PyDoc_STRVAR(get_main_doc,
@@ -481,7 +767,7 @@ _interp_exec(PyObject *self,
              PyObject **p_excinfo)
 {
     // Look up the interpreter.
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id_arg);
+    PyInterpreterState *interp = look_up_interp(id_arg);
     if (interp == NULL) {
         return -1;
     }
@@ -667,7 +953,7 @@ interp_is_running(PyObject *self, PyObject *args, PyObject *kwds)
         return NULL;
     }
 
-    PyInterpreterState *interp = PyInterpreterID_LookUp(id);
+    PyInterpreterState *interp = look_up_interp(id);
     if (interp == NULL) {
         return NULL;
     }
@@ -683,6 +969,49 @@ PyDoc_STRVAR(is_running_doc,
 Return whether or not the identified interpreter is running.");
 
 
+static PyObject *
+interp_incref(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"id", NULL};
+    PyObject *id;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O:_incref", kwlist, &id)) {
+        return NULL;
+    }
+
+    PyInterpreterState *interp = look_up_interp(id);
+    if (interp == NULL) {
+        return NULL;
+    }
+    if (_PyInterpreterState_IDInitref(interp) < 0) {
+        return NULL;
+    }
+    _PyInterpreterState_IDIncref(interp);
+
+    Py_RETURN_NONE;
+}
+
+
+static PyObject *
+interp_decref(PyObject *self, PyObject *args, PyObject *kwds)
+{
+    static char *kwlist[] = {"id", NULL};
+    PyObject *id;
+    if (!PyArg_ParseTupleAndKeywords(args, kwds,
+                                     "O:_incref", kwlist, &id)) {
+        return NULL;
+    }
+
+    PyInterpreterState *interp = look_up_interp(id);
+    if (interp == NULL) {
+        return NULL;
+    }
+    _PyInterpreterState_IDDecref(interp);
+
+    Py_RETURN_NONE;
+}
+
+
 static PyMethodDef module_functions[] = {
     {"create",                    _PyCFunction_CAST(interp_create),
      METH_VARARGS | METH_KEYWORDS, create_doc},
@@ -707,6 +1036,11 @@ static PyMethodDef module_functions[] = {
     {"is_shareable",              _PyCFunction_CAST(object_is_shareable),
      METH_VARARGS | METH_KEYWORDS, is_shareable_doc},
 
+    {"_incref",                   _PyCFunction_CAST(interp_incref),
+     METH_VARARGS | METH_KEYWORDS, NULL},
+    {"_decref",                   _PyCFunction_CAST(interp_decref),
+     METH_VARARGS | METH_KEYWORDS, NULL},
+
     {NULL,                        NULL}           /* sentinel */
 };
 
@@ -720,8 +1054,17 @@ The 'interpreters' module provides a more convenient interface.");
 static int
 module_exec(PyObject *mod)
 {
-    // PyInterpreterID
+    module_state *state = get_module_state(mod);
-    if (PyModule_AddType(mod, &PyInterpreterID_Type) < 0) {
+
+    // exceptions
+    if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterError) < 0) {
+        goto error;
+    }
+    if (PyModule_AddType(mod, (PyTypeObject *)PyExc_InterpreterNotFoundError) < 0) {
+        goto error;
+    }
+
+    if (register_memoryview_xid(mod, &state->XIBufferViewType) < 0) {
         goto error;
     }
 

Python/crossinterp.c

@@ -12,6 +12,53 @@
 #include "pycore_weakref.h"       // _PyWeakref_GET_REF()
 
 
+/**************/
+/* exceptions */
+/**************/
+
+/* InterpreterError extends Exception */
+
+static PyTypeObject _PyExc_InterpreterError = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    .tp_name = "InterpreterError",
+    .tp_doc = PyDoc_STR("An interpreter was not found."),
+    //.tp_base = (PyTypeObject *)PyExc_BaseException,
+};
+PyObject *PyExc_InterpreterError = (PyObject *)&_PyExc_InterpreterError;
+
+/* InterpreterNotFoundError extends InterpreterError */
+
+static PyTypeObject _PyExc_InterpreterNotFoundError = {
+    PyVarObject_HEAD_INIT(NULL, 0)
+    .tp_name = "InterpreterNotFoundError",
+    .tp_doc = PyDoc_STR("An interpreter was not found."),
+    .tp_base = &_PyExc_InterpreterError,
+};
+PyObject *PyExc_InterpreterNotFoundError = (PyObject *)&_PyExc_InterpreterNotFoundError;
+
+/* lifecycle */
+
+static int
+init_exceptions(PyInterpreterState *interp)
+{
+    _PyExc_InterpreterError.tp_base = (PyTypeObject *)PyExc_BaseException;
+    if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterError) < 0) {
+        return -1;
+    }
+    if (_PyStaticType_InitBuiltin(interp, &_PyExc_InterpreterNotFoundError) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+static void
+fini_exceptions(PyInterpreterState *interp)
+{
+    _PyStaticType_Dealloc(interp, &_PyExc_InterpreterNotFoundError);
+    _PyStaticType_Dealloc(interp, &_PyExc_InterpreterError);
+}
+
+
 /***************************/
 /* cross-interpreter calls */
 /***************************/
@@ -2099,3 +2146,18 @@ _PyXI_Fini(PyInterpreterState *interp)
         _xidregistry_fini(_get_global_xidregistry(interp->runtime));
     }
 }
+
+PyStatus
+_PyXI_InitTypes(PyInterpreterState *interp)
+{
+    if (init_exceptions(interp) < 0) {
+        return _PyStatus_ERR("failed to initialize an exception type");
+    }
+    return _PyStatus_OK();
+}
+
+void
+_PyXI_FiniTypes(PyInterpreterState *interp)
+{
+    fini_exceptions(interp);
+}

Python/pylifecycle.c

@@ -734,6 +734,11 @@ pycore_init_types(PyInterpreterState *interp)
         return status;
     }
 
+    status = _PyXI_InitTypes(interp);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
+
     return _PyStatus_OK();
 }
 
@@ -1742,6 +1747,7 @@ finalize_interp_types(PyInterpreterState *interp)
 {
     _PyUnicode_FiniTypes(interp);
     _PySys_FiniTypes(interp);
+    _PyXI_FiniTypes(interp);
     _PyExc_Fini(interp);
     _PyAsyncGen_Fini(interp);
     _PyContext_Fini(interp);

Python/pystate.c

@@ -1216,7 +1216,7 @@ _PyInterpreterState_LookUpID(int64_t requested_id)
         HEAD_UNLOCK(runtime);
     }
     if (interp == NULL && !PyErr_Occurred()) {
-        PyErr_Format(PyExc_RuntimeError,
+        PyErr_Format(PyExc_InterpreterNotFoundError,
                      "unrecognized interpreter ID %lld", requested_id);
     }
     return interp;

Tools/c-analyzer/cpython/globals-to-fix.tsv

@@ -290,6 +290,10 @@ Objects/exceptions.c	-	PyExc_UnicodeWarning	-
 Objects/exceptions.c	-	PyExc_BytesWarning	-
 Objects/exceptions.c	-	PyExc_ResourceWarning	-
 Objects/exceptions.c	-	PyExc_EncodingWarning	-
+Python/crossinterp.c	-	_PyExc_InterpreterError	-
+Python/crossinterp.c	-	_PyExc_InterpreterNotFoundError	-
+Python/crossinterp.c	-	PyExc_InterpreterError	-
+Python/crossinterp.c	-	PyExc_InterpreterNotFoundError	-
 
 ##-----------------------
 ## singletons