410 lines
12 KiB
Python
410 lines
12 KiB
Python
###############################################################################
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# Synchronization primitives based on our SemLock implementation
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#
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# author: Thomas Moreau and Olivier Grisel
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#
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# adapted from multiprocessing/synchronize.py (17/02/2017)
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# * Remove ctx argument for compatibility reason
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# * Registers a cleanup function with the loky resource_tracker to remove the
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# semaphore when the process dies instead.
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#
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# TODO: investigate which Python version is required to be able to use
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# multiprocessing.resource_tracker and therefore multiprocessing.synchronize
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# instead of a loky-specific fork.
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import os
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import sys
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import tempfile
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import threading
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import _multiprocessing
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from time import time as _time
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from multiprocessing import process, util
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from multiprocessing.context import assert_spawning
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from . import resource_tracker
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__all__ = [
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"Lock",
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"RLock",
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"Semaphore",
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"BoundedSemaphore",
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"Condition",
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"Event",
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]
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# Try to import the mp.synchronize module cleanly, if it fails
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# raise ImportError for platforms lacking a working sem_open implementation.
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# See issue 3770
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try:
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from _multiprocessing import SemLock as _SemLock
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from _multiprocessing import sem_unlink
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except ImportError:
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raise ImportError(
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"This platform lacks a functioning sem_open"
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" implementation, therefore, the required"
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" synchronization primitives needed will not"
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" function, see issue 3770."
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)
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#
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# Constants
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#
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RECURSIVE_MUTEX, SEMAPHORE = range(2)
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SEM_VALUE_MAX = _multiprocessing.SemLock.SEM_VALUE_MAX
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#
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# Base class for semaphores and mutexes; wraps `_multiprocessing.SemLock`
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#
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class SemLock:
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_rand = tempfile._RandomNameSequence()
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def __init__(self, kind, value, maxvalue, name=None):
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# unlink_now is only used on win32 or when we are using fork.
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unlink_now = False
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if name is None:
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# Try to find an unused name for the SemLock instance.
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for _ in range(100):
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try:
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self._semlock = _SemLock(
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kind, value, maxvalue, SemLock._make_name(), unlink_now
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)
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except FileExistsError: # pragma: no cover
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pass
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else:
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break
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else: # pragma: no cover
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raise FileExistsError("cannot find name for semaphore")
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else:
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self._semlock = _SemLock(kind, value, maxvalue, name, unlink_now)
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self.name = name
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util.debug(
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f"created semlock with handle {self._semlock.handle} and name "
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f'"{self.name}"'
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)
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self._make_methods()
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def _after_fork(obj):
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obj._semlock._after_fork()
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util.register_after_fork(self, _after_fork)
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# When the object is garbage collected or the
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# process shuts down we unlink the semaphore name
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resource_tracker.register(self._semlock.name, "semlock")
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util.Finalize(
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self, SemLock._cleanup, (self._semlock.name,), exitpriority=0
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)
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@staticmethod
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def _cleanup(name):
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try:
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sem_unlink(name)
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except FileNotFoundError:
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# Already unlinked, possibly by user code: ignore and make sure to
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# unregister the semaphore from the resource tracker.
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pass
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finally:
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resource_tracker.unregister(name, "semlock")
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def _make_methods(self):
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self.acquire = self._semlock.acquire
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self.release = self._semlock.release
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def __enter__(self):
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return self._semlock.acquire()
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def __exit__(self, *args):
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return self._semlock.release()
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def __getstate__(self):
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assert_spawning(self)
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sl = self._semlock
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h = sl.handle
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return (h, sl.kind, sl.maxvalue, sl.name)
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def __setstate__(self, state):
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self._semlock = _SemLock._rebuild(*state)
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util.debug(
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f'recreated blocker with handle {state[0]!r} and name "{state[3]}"'
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)
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self._make_methods()
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@staticmethod
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def _make_name():
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# OSX does not support long names for semaphores
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return f"/loky-{os.getpid()}-{next(SemLock._rand)}"
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#
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# Semaphore
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#
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class Semaphore(SemLock):
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def __init__(self, value=1):
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SemLock.__init__(self, SEMAPHORE, value, SEM_VALUE_MAX)
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def get_value(self):
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if sys.platform == "darwin":
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raise NotImplementedError("OSX does not implement sem_getvalue")
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return self._semlock._get_value()
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def __repr__(self):
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try:
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value = self._semlock._get_value()
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except Exception:
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value = "unknown"
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return f"<{self.__class__.__name__}(value={value})>"
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#
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# Bounded semaphore
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#
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class BoundedSemaphore(Semaphore):
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def __init__(self, value=1):
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SemLock.__init__(self, SEMAPHORE, value, value)
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def __repr__(self):
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try:
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value = self._semlock._get_value()
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except Exception:
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value = "unknown"
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return (
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f"<{self.__class__.__name__}(value={value}, "
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f"maxvalue={self._semlock.maxvalue})>"
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)
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#
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# Non-recursive lock
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#
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class Lock(SemLock):
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def __init__(self):
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super().__init__(SEMAPHORE, 1, 1)
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def __repr__(self):
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try:
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if self._semlock._is_mine():
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name = process.current_process().name
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if threading.current_thread().name != "MainThread":
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name = f"{name}|{threading.current_thread().name}"
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elif self._semlock._get_value() == 1:
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name = "None"
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elif self._semlock._count() > 0:
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name = "SomeOtherThread"
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else:
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name = "SomeOtherProcess"
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except Exception:
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name = "unknown"
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return f"<{self.__class__.__name__}(owner={name})>"
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#
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# Recursive lock
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#
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class RLock(SemLock):
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def __init__(self):
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super().__init__(RECURSIVE_MUTEX, 1, 1)
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def __repr__(self):
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try:
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if self._semlock._is_mine():
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name = process.current_process().name
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if threading.current_thread().name != "MainThread":
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name = f"{name}|{threading.current_thread().name}"
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count = self._semlock._count()
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elif self._semlock._get_value() == 1:
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name, count = "None", 0
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elif self._semlock._count() > 0:
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name, count = "SomeOtherThread", "nonzero"
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else:
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name, count = "SomeOtherProcess", "nonzero"
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except Exception:
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name, count = "unknown", "unknown"
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return f"<{self.__class__.__name__}({name}, {count})>"
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#
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# Condition variable
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#
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class Condition:
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def __init__(self, lock=None):
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self._lock = lock or RLock()
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self._sleeping_count = Semaphore(0)
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self._woken_count = Semaphore(0)
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self._wait_semaphore = Semaphore(0)
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self._make_methods()
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def __getstate__(self):
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assert_spawning(self)
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return (
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self._lock,
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self._sleeping_count,
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self._woken_count,
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self._wait_semaphore,
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)
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def __setstate__(self, state):
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(
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self._lock,
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self._sleeping_count,
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self._woken_count,
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self._wait_semaphore,
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) = state
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self._make_methods()
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def __enter__(self):
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return self._lock.__enter__()
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def __exit__(self, *args):
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return self._lock.__exit__(*args)
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def _make_methods(self):
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self.acquire = self._lock.acquire
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self.release = self._lock.release
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def __repr__(self):
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try:
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num_waiters = (
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self._sleeping_count._semlock._get_value()
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- self._woken_count._semlock._get_value()
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)
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except Exception:
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num_waiters = "unknown"
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return f"<{self.__class__.__name__}({self._lock}, {num_waiters})>"
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def wait(self, timeout=None):
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assert (
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self._lock._semlock._is_mine()
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), "must acquire() condition before using wait()"
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# indicate that this thread is going to sleep
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self._sleeping_count.release()
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# release lock
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count = self._lock._semlock._count()
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for _ in range(count):
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self._lock.release()
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try:
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# wait for notification or timeout
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return self._wait_semaphore.acquire(True, timeout)
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finally:
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# indicate that this thread has woken
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self._woken_count.release()
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# reacquire lock
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for _ in range(count):
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self._lock.acquire()
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def notify(self):
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assert self._lock._semlock._is_mine(), "lock is not owned"
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assert not self._wait_semaphore.acquire(False)
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# to take account of timeouts since last notify() we subtract
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# woken_count from sleeping_count and rezero woken_count
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while self._woken_count.acquire(False):
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res = self._sleeping_count.acquire(False)
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assert res
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if self._sleeping_count.acquire(False): # try grabbing a sleeper
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self._wait_semaphore.release() # wake up one sleeper
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self._woken_count.acquire() # wait for the sleeper to wake
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# rezero _wait_semaphore in case a timeout just happened
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self._wait_semaphore.acquire(False)
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def notify_all(self):
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assert self._lock._semlock._is_mine(), "lock is not owned"
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assert not self._wait_semaphore.acquire(False)
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# to take account of timeouts since last notify*() we subtract
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# woken_count from sleeping_count and rezero woken_count
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while self._woken_count.acquire(False):
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res = self._sleeping_count.acquire(False)
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assert res
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sleepers = 0
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while self._sleeping_count.acquire(False):
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self._wait_semaphore.release() # wake up one sleeper
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sleepers += 1
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if sleepers:
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for _ in range(sleepers):
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self._woken_count.acquire() # wait for a sleeper to wake
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# rezero wait_semaphore in case some timeouts just happened
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while self._wait_semaphore.acquire(False):
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pass
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def wait_for(self, predicate, timeout=None):
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result = predicate()
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if result:
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return result
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if timeout is not None:
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endtime = _time() + timeout
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else:
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endtime = None
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waittime = None
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while not result:
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if endtime is not None:
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waittime = endtime - _time()
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if waittime <= 0:
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break
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self.wait(waittime)
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result = predicate()
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return result
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#
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# Event
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#
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class Event:
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def __init__(self):
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self._cond = Condition(Lock())
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self._flag = Semaphore(0)
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def is_set(self):
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with self._cond:
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if self._flag.acquire(False):
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self._flag.release()
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return True
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return False
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def set(self):
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with self._cond:
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self._flag.acquire(False)
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self._flag.release()
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self._cond.notify_all()
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def clear(self):
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with self._cond:
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self._flag.acquire(False)
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def wait(self, timeout=None):
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with self._cond:
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if self._flag.acquire(False):
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self._flag.release()
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else:
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self._cond.wait(timeout)
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if self._flag.acquire(False):
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self._flag.release()
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return True
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return False
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