asyncio: Refactor SIGCHLD handling. By Anthony Baire.

This commit is contained in:
Guido van Rossum 2013-11-04 15:50:46 -08:00
parent ccea08462b
commit 0eaa5ac9b5
5 changed files with 1315 additions and 199 deletions

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@ -1,10 +1,11 @@
"""Event loop and event loop policy."""
__all__ = ['AbstractEventLoopPolicy', 'DefaultEventLoopPolicy',
__all__ = ['AbstractEventLoopPolicy',
'AbstractEventLoop', 'AbstractServer',
'Handle', 'TimerHandle',
'get_event_loop_policy', 'set_event_loop_policy',
'get_event_loop', 'set_event_loop', 'new_event_loop',
'get_child_watcher', 'set_child_watcher',
]
import subprocess
@ -318,8 +319,18 @@ class AbstractEventLoopPolicy:
"""XXX"""
raise NotImplementedError
# Child processes handling (Unix only).
class DefaultEventLoopPolicy(threading.local, AbstractEventLoopPolicy):
def get_child_watcher(self):
"""XXX"""
raise NotImplementedError
def set_child_watcher(self, watcher):
"""XXX"""
raise NotImplementedError
class BaseDefaultEventLoopPolicy(AbstractEventLoopPolicy):
"""Default policy implementation for accessing the event loop.
In this policy, each thread has its own event loop. However, we
@ -332,28 +343,34 @@ class DefaultEventLoopPolicy(threading.local, AbstractEventLoopPolicy):
associated).
"""
_loop = None
_set_called = False
_loop_factory = None
class _Local(threading.local):
_loop = None
_set_called = False
def __init__(self):
self._local = self._Local()
def get_event_loop(self):
"""Get the event loop.
This may be None or an instance of EventLoop.
"""
if (self._loop is None and
not self._set_called and
if (self._local._loop is None and
not self._local._set_called and
isinstance(threading.current_thread(), threading._MainThread)):
self._loop = self.new_event_loop()
assert self._loop is not None, \
self._local._loop = self.new_event_loop()
assert self._local._loop is not None, \
('There is no current event loop in thread %r.' %
threading.current_thread().name)
return self._loop
return self._local._loop
def set_event_loop(self, loop):
"""Set the event loop."""
self._set_called = True
self._local._set_called = True
assert loop is None or isinstance(loop, AbstractEventLoop)
self._loop = loop
self._local._loop = loop
def new_event_loop(self):
"""Create a new event loop.
@ -361,12 +378,7 @@ class DefaultEventLoopPolicy(threading.local, AbstractEventLoopPolicy):
You must call set_event_loop() to make this the current event
loop.
"""
if sys.platform == 'win32': # pragma: no cover
from . import windows_events
return windows_events.SelectorEventLoop()
else: # pragma: no cover
from . import unix_events
return unix_events.SelectorEventLoop()
return self._loop_factory()
# Event loop policy. The policy itself is always global, even if the
@ -375,12 +387,22 @@ class DefaultEventLoopPolicy(threading.local, AbstractEventLoopPolicy):
# call to get_event_loop_policy().
_event_loop_policy = None
# Lock for protecting the on-the-fly creation of the event loop policy.
_lock = threading.Lock()
def _init_event_loop_policy():
global _event_loop_policy
with _lock:
if _event_loop_policy is None: # pragma: no branch
from . import DefaultEventLoopPolicy
_event_loop_policy = DefaultEventLoopPolicy()
def get_event_loop_policy():
"""XXX"""
global _event_loop_policy
if _event_loop_policy is None:
_event_loop_policy = DefaultEventLoopPolicy()
_init_event_loop_policy()
return _event_loop_policy
@ -404,3 +426,13 @@ def set_event_loop(loop):
def new_event_loop():
"""XXX"""
return get_event_loop_policy().new_event_loop()
def get_child_watcher():
"""XXX"""
return get_event_loop_policy().get_child_watcher()
def set_child_watcher(watcher):
"""XXX"""
return get_event_loop_policy().set_child_watcher(watcher)

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@ -8,6 +8,7 @@ import socket
import stat
import subprocess
import sys
import threading
from . import base_subprocess
@ -20,7 +21,10 @@ from . import transports
from .log import logger
__all__ = ['SelectorEventLoop', 'STDIN', 'STDOUT', 'STDERR']
__all__ = ['SelectorEventLoop', 'STDIN', 'STDOUT', 'STDERR',
'AbstractChildWatcher', 'SafeChildWatcher',
'FastChildWatcher', 'DefaultEventLoopPolicy',
]
STDIN = 0
STDOUT = 1
@ -31,7 +35,7 @@ if sys.platform == 'win32': # pragma: no cover
raise ImportError('Signals are not really supported on Windows')
class SelectorEventLoop(selector_events.BaseSelectorEventLoop):
class _UnixSelectorEventLoop(selector_events.BaseSelectorEventLoop):
"""Unix event loop
Adds signal handling to SelectorEventLoop
@ -40,17 +44,10 @@ class SelectorEventLoop(selector_events.BaseSelectorEventLoop):
def __init__(self, selector=None):
super().__init__(selector)
self._signal_handlers = {}
self._subprocesses = {}
def _socketpair(self):
return socket.socketpair()
def close(self):
handler = self._signal_handlers.get(signal.SIGCHLD)
if handler is not None:
self.remove_signal_handler(signal.SIGCHLD)
super().close()
def add_signal_handler(self, sig, callback, *args):
"""Add a handler for a signal. UNIX only.
@ -152,49 +149,20 @@ class SelectorEventLoop(selector_events.BaseSelectorEventLoop):
def _make_subprocess_transport(self, protocol, args, shell,
stdin, stdout, stderr, bufsize,
extra=None, **kwargs):
self._reg_sigchld()
transp = _UnixSubprocessTransport(self, protocol, args, shell,
stdin, stdout, stderr, bufsize,
extra=None, **kwargs)
self._subprocesses[transp.get_pid()] = transp
with events.get_child_watcher() as watcher:
transp = _UnixSubprocessTransport(self, protocol, args, shell,
stdin, stdout, stderr, bufsize,
extra=None, **kwargs)
watcher.add_child_handler(transp.get_pid(),
self._child_watcher_callback, transp)
yield from transp._post_init()
return transp
def _reg_sigchld(self):
if signal.SIGCHLD not in self._signal_handlers:
self.add_signal_handler(signal.SIGCHLD, self._sig_chld)
def _child_watcher_callback(self, pid, returncode, transp):
self.call_soon_threadsafe(transp._process_exited, returncode)
def _sig_chld(self):
try:
# Because of signal coalescing, we must keep calling waitpid() as
# long as we're able to reap a child.
while True:
try:
pid, status = os.waitpid(-1, os.WNOHANG)
except ChildProcessError:
break # No more child processes exist.
if pid == 0:
break # All remaining child processes are still alive.
elif os.WIFSIGNALED(status):
# A child process died because of a signal.
returncode = -os.WTERMSIG(status)
elif os.WIFEXITED(status):
# A child process exited (e.g. sys.exit()).
returncode = os.WEXITSTATUS(status)
else:
# A child exited, but we don't understand its status.
# This shouldn't happen, but if it does, let's just
# return that status; perhaps that helps debug it.
returncode = status
transp = self._subprocesses.get(pid)
if transp is not None:
transp._process_exited(returncode)
except Exception:
logger.exception('Unknown exception in SIGCHLD handler')
def _subprocess_closed(self, transport):
pid = transport.get_pid()
self._subprocesses.pop(pid, None)
def _subprocess_closed(self, transp):
pass
def _set_nonblocking(fd):
@ -423,3 +391,335 @@ class _UnixSubprocessTransport(base_subprocess.BaseSubprocessTransport):
if stdin_w is not None:
stdin.close()
self._proc.stdin = open(stdin_w.detach(), 'rb', buffering=bufsize)
class AbstractChildWatcher:
"""Abstract base class for monitoring child processes.
Objects derived from this class monitor a collection of subprocesses and
report their termination or interruption by a signal.
New callbacks are registered with .add_child_handler(). Starting a new
process must be done within a 'with' block to allow the watcher to suspend
its activity until the new process if fully registered (this is needed to
prevent a race condition in some implementations).
Example:
with watcher:
proc = subprocess.Popen("sleep 1")
watcher.add_child_handler(proc.pid, callback)
Notes:
Implementations of this class must be thread-safe.
Since child watcher objects may catch the SIGCHLD signal and call
waitpid(-1), there should be only one active object per process.
"""
def add_child_handler(self, pid, callback, *args):
"""Register a new child handler.
Arrange for callback(pid, returncode, *args) to be called when
process 'pid' terminates. Specifying another callback for the same
process replaces the previous handler.
Note: callback() must be thread-safe
"""
raise NotImplementedError()
def remove_child_handler(self, pid):
"""Removes the handler for process 'pid'.
The function returns True if the handler was successfully removed,
False if there was nothing to remove."""
raise NotImplementedError()
def set_loop(self, loop):
"""Reattach the watcher to another event loop.
Note: loop may be None
"""
raise NotImplementedError()
def close(self):
"""Close the watcher.
This must be called to make sure that any underlying resource is freed.
"""
raise NotImplementedError()
def __enter__(self):
"""Enter the watcher's context and allow starting new processes
This function must return self"""
raise NotImplementedError()
def __exit__(self, a, b, c):
"""Exit the watcher's context"""
raise NotImplementedError()
class BaseChildWatcher(AbstractChildWatcher):
def __init__(self, loop):
self._loop = None
self._callbacks = {}
self.set_loop(loop)
def close(self):
self.set_loop(None)
self._callbacks.clear()
def _do_waitpid(self, expected_pid):
raise NotImplementedError()
def _do_waitpid_all(self):
raise NotImplementedError()
def set_loop(self, loop):
assert loop is None or isinstance(loop, events.AbstractEventLoop)
if self._loop is not None:
self._loop.remove_signal_handler(signal.SIGCHLD)
self._loop = loop
if loop is not None:
loop.add_signal_handler(signal.SIGCHLD, self._sig_chld)
# Prevent a race condition in case a child terminated
# during the switch.
self._do_waitpid_all()
def remove_child_handler(self, pid):
try:
del self._callbacks[pid]
return True
except KeyError:
return False
def _sig_chld(self):
try:
self._do_waitpid_all()
except Exception:
logger.exception('Unknown exception in SIGCHLD handler')
def _compute_returncode(self, status):
if os.WIFSIGNALED(status):
# The child process died because of a signal.
return -os.WTERMSIG(status)
elif os.WIFEXITED(status):
# The child process exited (e.g sys.exit()).
return os.WEXITSTATUS(status)
else:
# The child exited, but we don't understand its status.
# This shouldn't happen, but if it does, let's just
# return that status; perhaps that helps debug it.
return status
class SafeChildWatcher(BaseChildWatcher):
"""'Safe' child watcher implementation.
This implementation avoids disrupting other code spawning processes by
polling explicitly each process in the SIGCHLD handler instead of calling
os.waitpid(-1).
This is a safe solution but it has a significant overhead when handling a
big number of children (O(n) each time SIGCHLD is raised)
"""
def __enter__(self):
return self
def __exit__(self, a, b, c):
pass
def add_child_handler(self, pid, callback, *args):
self._callbacks[pid] = callback, args
# Prevent a race condition in case the child is already terminated.
self._do_waitpid(pid)
def _do_waitpid_all(self):
for pid in list(self._callbacks):
self._do_waitpid(pid)
def _do_waitpid(self, expected_pid):
assert expected_pid > 0
try:
pid, status = os.waitpid(expected_pid, os.WNOHANG)
except ChildProcessError:
# The child process is already reaped
# (may happen if waitpid() is called elsewhere).
pid = expected_pid
returncode = 255
logger.warning(
"Unknown child process pid %d, will report returncode 255",
pid)
else:
if pid == 0:
# The child process is still alive.
return
returncode = self._compute_returncode(status)
try:
callback, args = self._callbacks.pop(pid)
except KeyError: # pragma: no cover
# May happen if .remove_child_handler() is called
# after os.waitpid() returns.
pass
else:
callback(pid, returncode, *args)
class FastChildWatcher(BaseChildWatcher):
"""'Fast' child watcher implementation.
This implementation reaps every terminated processes by calling
os.waitpid(-1) directly, possibly breaking other code spawning processes
and waiting for their termination.
There is no noticeable overhead when handling a big number of children
(O(1) each time a child terminates).
"""
def __init__(self, loop):
super().__init__(loop)
self._lock = threading.Lock()
self._zombies = {}
self._forks = 0
def close(self):
super().close()
self._zombies.clear()
def __enter__(self):
with self._lock:
self._forks += 1
return self
def __exit__(self, a, b, c):
with self._lock:
self._forks -= 1
if self._forks or not self._zombies:
return
collateral_victims = str(self._zombies)
self._zombies.clear()
logger.warning(
"Caught subprocesses termination from unknown pids: %s",
collateral_victims)
def add_child_handler(self, pid, callback, *args):
assert self._forks, "Must use the context manager"
self._callbacks[pid] = callback, args
try:
# Ensure that the child is not already terminated.
# (raise KeyError if still alive)
returncode = self._zombies.pop(pid)
# Child is dead, therefore we can fire the callback immediately.
# First we remove it from the dict.
# (raise KeyError if .remove_child_handler() was called in-between)
del self._callbacks[pid]
except KeyError:
pass
else:
callback(pid, returncode, *args)
def _do_waitpid_all(self):
# Because of signal coalescing, we must keep calling waitpid() as
# long as we're able to reap a child.
while True:
try:
pid, status = os.waitpid(-1, os.WNOHANG)
except ChildProcessError:
# No more child processes exist.
return
else:
if pid == 0:
# A child process is still alive.
return
returncode = self._compute_returncode(status)
try:
callback, args = self._callbacks.pop(pid)
except KeyError:
# unknown child
with self._lock:
if self._forks:
# It may not be registered yet.
self._zombies[pid] = returncode
continue
logger.warning(
"Caught subprocess termination from unknown pid: "
"%d -> %d", pid, returncode)
else:
callback(pid, returncode, *args)
class _UnixDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
"""XXX"""
_loop_factory = _UnixSelectorEventLoop
def __init__(self):
super().__init__()
self._watcher = None
def _init_watcher(self):
with events._lock:
if self._watcher is None: # pragma: no branch
if isinstance(threading.current_thread(),
threading._MainThread):
self._watcher = SafeChildWatcher(self._local._loop)
else:
self._watcher = SafeChildWatcher(None)
def set_event_loop(self, loop):
"""Set the event loop.
As a side effect, if a child watcher was set before, then calling
.set_event_loop() from the main thread will call .set_loop(loop) on the
child watcher.
"""
super().set_event_loop(loop)
if self._watcher is not None and \
isinstance(threading.current_thread(), threading._MainThread):
self._watcher.set_loop(loop)
def get_child_watcher(self):
"""Get the child watcher
If not yet set, a SafeChildWatcher object is automatically created.
"""
if self._watcher is None:
self._init_watcher()
return self._watcher
def set_child_watcher(self, watcher):
"""Set the child watcher"""
assert watcher is None or isinstance(watcher, AbstractChildWatcher)
if self._watcher is not None:
self._watcher.close()
self._watcher = watcher
SelectorEventLoop = _UnixSelectorEventLoop
DefaultEventLoopPolicy = _UnixDefaultEventLoopPolicy

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@ -7,6 +7,7 @@ import weakref
import struct
import _winapi
from . import events
from . import base_subprocess
from . import futures
from . import proactor_events
@ -17,7 +18,9 @@ from .log import logger
from . import _overlapped
__all__ = ['SelectorEventLoop', 'ProactorEventLoop', 'IocpProactor']
__all__ = ['SelectorEventLoop', 'ProactorEventLoop', 'IocpProactor',
'DefaultEventLoopPolicy',
]
NULL = 0
@ -108,7 +111,7 @@ class PipeServer(object):
__del__ = close
class SelectorEventLoop(selector_events.BaseSelectorEventLoop):
class _WindowsSelectorEventLoop(selector_events.BaseSelectorEventLoop):
"""Windows version of selector event loop."""
def _socketpair(self):
@ -453,3 +456,13 @@ class _WindowsSubprocessTransport(base_subprocess.BaseSubprocessTransport):
f = self._loop._proactor.wait_for_handle(int(self._proc._handle))
f.add_done_callback(callback)
SelectorEventLoop = _WindowsSelectorEventLoop
class _WindowsDefaultEventLoopPolicy(events.BaseDefaultEventLoopPolicy):
_loop_factory = SelectorEventLoop
DefaultEventLoopPolicy = _WindowsDefaultEventLoopPolicy

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@ -1308,8 +1308,17 @@ else:
from asyncio import selectors
from asyncio import unix_events
class UnixEventLoopTestsMixin(EventLoopTestsMixin):
def setUp(self):
super().setUp()
events.set_child_watcher(unix_events.SafeChildWatcher(self.loop))
def tearDown(self):
events.set_child_watcher(None)
super().tearDown()
if hasattr(selectors, 'KqueueSelector'):
class KqueueEventLoopTests(EventLoopTestsMixin,
class KqueueEventLoopTests(UnixEventLoopTestsMixin,
SubprocessTestsMixin,
unittest.TestCase):
@ -1318,7 +1327,7 @@ else:
selectors.KqueueSelector())
if hasattr(selectors, 'EpollSelector'):
class EPollEventLoopTests(EventLoopTestsMixin,
class EPollEventLoopTests(UnixEventLoopTestsMixin,
SubprocessTestsMixin,
unittest.TestCase):
@ -1326,7 +1335,7 @@ else:
return unix_events.SelectorEventLoop(selectors.EpollSelector())
if hasattr(selectors, 'PollSelector'):
class PollEventLoopTests(EventLoopTestsMixin,
class PollEventLoopTests(UnixEventLoopTestsMixin,
SubprocessTestsMixin,
unittest.TestCase):
@ -1334,7 +1343,7 @@ else:
return unix_events.SelectorEventLoop(selectors.PollSelector())
# Should always exist.
class SelectEventLoopTests(EventLoopTestsMixin,
class SelectEventLoopTests(UnixEventLoopTestsMixin,
SubprocessTestsMixin,
unittest.TestCase):
@ -1557,25 +1566,36 @@ class ProtocolsAbsTests(unittest.TestCase):
class PolicyTests(unittest.TestCase):
def create_policy(self):
if sys.platform == "win32":
from asyncio import windows_events
return windows_events.DefaultEventLoopPolicy()
else:
from asyncio import unix_events
return unix_events.DefaultEventLoopPolicy()
def test_event_loop_policy(self):
policy = events.AbstractEventLoopPolicy()
self.assertRaises(NotImplementedError, policy.get_event_loop)
self.assertRaises(NotImplementedError, policy.set_event_loop, object())
self.assertRaises(NotImplementedError, policy.new_event_loop)
self.assertRaises(NotImplementedError, policy.get_child_watcher)
self.assertRaises(NotImplementedError, policy.set_child_watcher,
object())
def test_get_event_loop(self):
policy = events.DefaultEventLoopPolicy()
self.assertIsNone(policy._loop)
policy = self.create_policy()
self.assertIsNone(policy._local._loop)
loop = policy.get_event_loop()
self.assertIsInstance(loop, events.AbstractEventLoop)
self.assertIs(policy._loop, loop)
self.assertIs(policy._local._loop, loop)
self.assertIs(loop, policy.get_event_loop())
loop.close()
def test_get_event_loop_after_set_none(self):
policy = events.DefaultEventLoopPolicy()
policy = self.create_policy()
policy.set_event_loop(None)
self.assertRaises(AssertionError, policy.get_event_loop)
@ -1583,7 +1603,7 @@ class PolicyTests(unittest.TestCase):
def test_get_event_loop_thread(self, m_current_thread):
def f():
policy = events.DefaultEventLoopPolicy()
policy = self.create_policy()
self.assertRaises(AssertionError, policy.get_event_loop)
th = threading.Thread(target=f)
@ -1591,14 +1611,14 @@ class PolicyTests(unittest.TestCase):
th.join()
def test_new_event_loop(self):
policy = events.DefaultEventLoopPolicy()
policy = self.create_policy()
loop = policy.new_event_loop()
self.assertIsInstance(loop, events.AbstractEventLoop)
loop.close()
def test_set_event_loop(self):
policy = events.DefaultEventLoopPolicy()
policy = self.create_policy()
old_loop = policy.get_event_loop()
self.assertRaises(AssertionError, policy.set_event_loop, object())
@ -1621,7 +1641,7 @@ class PolicyTests(unittest.TestCase):
old_policy = events.get_event_loop_policy()
policy = events.DefaultEventLoopPolicy()
policy = self.create_policy()
events.set_event_loop_policy(policy)
self.assertIs(policy, events.get_event_loop_policy())
self.assertIsNot(policy, old_policy)

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