SF bug 1524317: configure --without-threads fails to build

Moved the code for _PyThread_CurrentFrames() up, so it's no longer
in a huge "#ifdef WITH_THREAD" block (I didn't realize it /was/ in
one).

Changed test_sys's test_current_frames() so it passes with or without
thread supported compiled in.

Note that test_sys fails when Python is compiled without threads,
but for an unrelated reason (the old test_exit() fails with an
indirect ImportError on the `thread` module).  There are also
other unrelated compilation failures without threads, in extension
modules (like ctypes); at least the core compiles again.

Do we really support --without-threads?  If so, there are several
problems remaining.

Lib/test/test_sys.py

@@ -239,6 +239,19 @@ class SysModuleTest(unittest.TestCase):
 
     # sys._current_frames() is a CPython-only gimmick.
     def test_current_frames(self):
+        have_threads = True
+        try:
+            import thread
+        except ImportError:
+            have_threads = False
+
+        if have_threads:
+            self.current_frames_with_threads()
+        else:
+            self.current_frames_without_threads()
+
+    # Test sys._current_frames() in a WITH_THREADS build.
+    def current_frames_with_threads(self):
         import threading, thread
         import traceback
 
@@ -298,6 +311,15 @@ class SysModuleTest(unittest.TestCase):
         leave_g.set()
         t.join()
 
+    # Test sys._current_frames() when thread support doesn't exist.
+    def current_frames_without_threads(self):
+        # Not much happens here:  there is only one thread, with artificial
+        # "thread id" 0.
+        d = sys._current_frames()
+        self.assertEqual(len(d), 1)
+        self.assert_(0 in d)
+        self.assert_(d[0] is sys._getframe())
+
     def test_attributes(self):
         self.assert_(isinstance(sys.api_version, int))
         self.assert_(isinstance(sys.argv, list))

Misc/NEWS

@@ -24,6 +24,11 @@ Core and builtins
   again.  Fixing this problem required changing the .pyc magic number.
   This means that .pyc files generated before 2.5c1 will be regenerated.
 
+- Bug #1524317:  Compiling Python ``--without-threads`` failed.
+  The Python core compiles again then, and, in a build without threads, the
+  new ``sys._current_frames()`` returns a dictionary with one entry,
+  mapping the faux "thread id" 0 to the current frame.
+
 Library
 -------
 

Python/pystate.c

@@ -387,6 +387,53 @@ PyThreadState_Next(PyThreadState *tstate) {
 	return tstate->next;
 }
 
+/* The implementation of sys._current_frames().  This is intended to be
+   called with the GIL held, as it will be when called via
+   sys._current_frames().  It's possible it would work fine even without
+   the GIL held, but haven't thought enough about that.
+*/
+PyObject *
+_PyThread_CurrentFrames(void)
+{
+	PyObject *result;
+	PyInterpreterState *i;
+
+	result = PyDict_New();
+	if (result == NULL)
+		return NULL;
+
+	/* for i in all interpreters:
+	 *     for t in all of i's thread states:
+	 *          if t's frame isn't NULL, map t's id to its frame
+	 * Because these lists can mutute even when the GIL is held, we
+	 * need to grab head_mutex for the duration.
+	 */
+	HEAD_LOCK();
+	for (i = interp_head; i != NULL; i = i->next) {
+		PyThreadState *t;
+		for (t = i->tstate_head; t != NULL; t = t->next) {
+			PyObject *id;
+			int stat;
+			struct _frame *frame = t->frame;
+			if (frame == NULL)
+				continue;
+			id = PyInt_FromLong(t->thread_id);
+			if (id == NULL)
+				goto Fail;
+			stat = PyDict_SetItem(result, id, (PyObject *)frame);
+			Py_DECREF(id);
+			if (stat < 0)
+				goto Fail;
+		}
+	}
+	HEAD_UNLOCK();
+	return result;
+
+ Fail:
+ 	HEAD_UNLOCK();
+ 	Py_DECREF(result);
+ 	return NULL;
+}
 
 /* Python "auto thread state" API. */
 #ifdef WITH_THREAD
@@ -550,54 +597,6 @@ PyGILState_Release(PyGILState_STATE oldstate)
 		PyEval_SaveThread();
 }
 
-/* The implementation of sys._current_frames().  This is intended to be
-   called with the GIL held, as it will be when called via
-   sys._current_frames().  It's possible it would work fine even without
-   the GIL held, but haven't thought enough about that.
-*/
-PyObject *
-_PyThread_CurrentFrames(void)
-{
-	PyObject *result;
-	PyInterpreterState *i;
-
-	result = PyDict_New();
-	if (result == NULL)
-		return NULL;
-
-	/* for i in all interpreters:
-	 *     for t in all of i's thread states:
-	 *          if t's frame isn't NULL, map t's id to its frame
-	 * Because these lists can mutute even when the GIL is held, we
-	 * need to grab head_mutex for the duration.
-	 */
-	HEAD_LOCK();
-	for (i = interp_head; i != NULL; i = i->next) {
-		PyThreadState *t;
-		for (t = i->tstate_head; t != NULL; t = t->next) {
-			PyObject *id;
-			int stat;
-			struct _frame *frame = t->frame;
-			if (frame == NULL)
-				continue;
-			id = PyInt_FromLong(t->thread_id);
-			if (id == NULL)
-				goto Fail;
-			stat = PyDict_SetItem(result, id, (PyObject *)frame);
-			Py_DECREF(id);
-			if (stat < 0)
-				goto Fail;
-		}
-	}
-	HEAD_UNLOCK();
-	return result;
-
- Fail:
- 	HEAD_UNLOCK();
- 	Py_DECREF(result);
- 	return NULL;
-}
-
 #ifdef __cplusplus
 }
 #endif