468 lines
14 KiB
Python
468 lines
14 KiB
Python
|
"""Synchronization primitives."""
|
||
|
|
|
||
|
|
__all__ = ['Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore']
|
||
|
|
|
||
|
|
import collections
|
||
|
|
|
||
|
|
from . import compat
|
||
|
|
from . import events
|
||
|
|
from . import futures
|
||
|
|
from .coroutines import coroutine
|
||
|
|
|
||
|
|
|
||
|
|
class _ContextManager:
|
||
|
|
"""Context manager.
|
||
|
|
|
||
|
|
This enables the following idiom for acquiring and releasing a
|
||
|
|
lock around a block:
|
||
|
|
|
||
|
|
with (yield from lock):
|
||
|
|
<block>
|
||
|
|
|
||
|
|
while failing loudly when accidentally using:
|
||
|
|
|
||
|
|
with lock:
|
||
|
|
<block>
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, lock):
|
||
|
|
self._lock = lock
|
||
|
|
|
||
|
|
def __enter__(self):
|
||
|
|
# We have no use for the "as ..." clause in the with
|
||
|
|
# statement for locks.
|
||
|
|
return None
|
||
|
|
|
||
|
|
def __exit__(self, *args):
|
||
|
|
try:
|
||
|
|
self._lock.release()
|
||
|
|
finally:
|
||
|
|
self._lock = None # Crudely prevent reuse.
|
||
|
|
|
||
|
|
|
||
|
|
class _ContextManagerMixin:
|
||
|
|
def __enter__(self):
|
||
|
|
raise RuntimeError(
|
||
|
|
'"yield from" should be used as context manager expression')
|
||
|
|
|
||
|
|
def __exit__(self, *args):
|
||
|
|
# This must exist because __enter__ exists, even though that
|
||
|
|
# always raises; that's how the with-statement works.
|
||
|
|
pass
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def __iter__(self):
|
||
|
|
# This is not a coroutine. It is meant to enable the idiom:
|
||
|
|
#
|
||
|
|
# with (yield from lock):
|
||
|
|
# <block>
|
||
|
|
#
|
||
|
|
# as an alternative to:
|
||
|
|
#
|
||
|
|
# yield from lock.acquire()
|
||
|
|
# try:
|
||
|
|
# <block>
|
||
|
|
# finally:
|
||
|
|
# lock.release()
|
||
|
|
yield from self.acquire()
|
||
|
|
return _ContextManager(self)
|
||
|
|
|
||
|
|
if compat.PY35:
|
||
|
|
|
||
|
|
def __await__(self):
|
||
|
|
# To make "with await lock" work.
|
||
|
|
yield from self.acquire()
|
||
|
|
return _ContextManager(self)
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def __aenter__(self):
|
||
|
|
yield from self.acquire()
|
||
|
|
# We have no use for the "as ..." clause in the with
|
||
|
|
# statement for locks.
|
||
|
|
return None
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def __aexit__(self, exc_type, exc, tb):
|
||
|
|
self.release()
|
||
|
|
|
||
|
|
|
||
|
|
class Lock(_ContextManagerMixin):
|
||
|
|
"""Primitive lock objects.
|
||
|
|
|
||
|
|
A primitive lock is a synchronization primitive that is not owned
|
||
|
|
by a particular coroutine when locked. A primitive lock is in one
|
||
|
|
of two states, 'locked' or 'unlocked'.
|
||
|
|
|
||
|
|
It is created in the unlocked state. It has two basic methods,
|
||
|
|
acquire() and release(). When the state is unlocked, acquire()
|
||
|
|
changes the state to locked and returns immediately. When the
|
||
|
|
state is locked, acquire() blocks until a call to release() in
|
||
|
|
another coroutine changes it to unlocked, then the acquire() call
|
||
|
|
resets it to locked and returns. The release() method should only
|
||
|
|
be called in the locked state; it changes the state to unlocked
|
||
|
|
and returns immediately. If an attempt is made to release an
|
||
|
|
unlocked lock, a RuntimeError will be raised.
|
||
|
|
|
||
|
|
When more than one coroutine is blocked in acquire() waiting for
|
||
|
|
the state to turn to unlocked, only one coroutine proceeds when a
|
||
|
|
release() call resets the state to unlocked; first coroutine which
|
||
|
|
is blocked in acquire() is being processed.
|
||
|
|
|
||
|
|
acquire() is a coroutine and should be called with 'yield from'.
|
||
|
|
|
||
|
|
Locks also support the context management protocol. '(yield from lock)'
|
||
|
|
should be used as context manager expression.
|
||
|
|
|
||
|
|
Usage:
|
||
|
|
|
||
|
|
lock = Lock()
|
||
|
|
...
|
||
|
|
yield from lock
|
||
|
|
try:
|
||
|
|
...
|
||
|
|
finally:
|
||
|
|
lock.release()
|
||
|
|
|
||
|
|
Context manager usage:
|
||
|
|
|
||
|
|
lock = Lock()
|
||
|
|
...
|
||
|
|
with (yield from lock):
|
||
|
|
...
|
||
|
|
|
||
|
|
Lock objects can be tested for locking state:
|
||
|
|
|
||
|
|
if not lock.locked():
|
||
|
|
yield from lock
|
||
|
|
else:
|
||
|
|
# lock is acquired
|
||
|
|
...
|
||
|
|
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, *, loop=None):
|
||
|
|
self._waiters = collections.deque()
|
||
|
|
self._locked = False
|
||
|
|
if loop is not None:
|
||
|
|
self._loop = loop
|
||
|
|
else:
|
||
|
|
self._loop = events.get_event_loop()
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
res = super().__repr__()
|
||
|
|
extra = 'locked' if self._locked else 'unlocked'
|
||
|
|
if self._waiters:
|
||
|
|
extra = '{},waiters:{}'.format(extra, len(self._waiters))
|
||
|
|
return '<{} [{}]>'.format(res[1:-1], extra)
|
||
|
|
|
||
|
|
def locked(self):
|
||
|
|
"""Return True if lock is acquired."""
|
||
|
|
return self._locked
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def acquire(self):
|
||
|
|
"""Acquire a lock.
|
||
|
|
|
||
|
|
This method blocks until the lock is unlocked, then sets it to
|
||
|
|
locked and returns True.
|
||
|
|
"""
|
||
|
|
if not self._waiters and not self._locked:
|
||
|
|
self._locked = True
|
||
|
|
return True
|
||
|
|
|
||
|
|
fut = futures.Future(loop=self._loop)
|
||
|
|
self._waiters.append(fut)
|
||
|
|
try:
|
||
|
|
yield from fut
|
||
|
|
self._locked = True
|
||
|
|
return True
|
||
|
|
finally:
|
||
|
|
self._waiters.remove(fut)
|
||
|
|
|
||
|
|
def release(self):
|
||
|
|
"""Release a lock.
|
||
|
|
|
||
|
|
When the lock is locked, reset it to unlocked, and return.
|
||
|
|
If any other coroutines are blocked waiting for the lock to become
|
||
|
|
unlocked, allow exactly one of them to proceed.
|
||
|
|
|
||
|
|
When invoked on an unlocked lock, a RuntimeError is raised.
|
||
|
|
|
||
|
|
There is no return value.
|
||
|
|
"""
|
||
|
|
if self._locked:
|
||
|
|
self._locked = False
|
||
|
|
# Wake up the first waiter who isn't cancelled.
|
||
|
|
for fut in self._waiters:
|
||
|
|
if not fut.done():
|
||
|
|
fut.set_result(True)
|
||
|
|
break
|
||
|
|
else:
|
||
|
|
raise RuntimeError('Lock is not acquired.')
|
||
|
|
|
||
|
|
|
||
|
|
class Event:
|
||
|
|
"""Asynchronous equivalent to threading.Event.
|
||
|
|
|
||
|
|
Class implementing event objects. An event manages a flag that can be set
|
||
|
|
to true with the set() method and reset to false with the clear() method.
|
||
|
|
The wait() method blocks until the flag is true. The flag is initially
|
||
|
|
false.
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, *, loop=None):
|
||
|
|
self._waiters = collections.deque()
|
||
|
|
self._value = False
|
||
|
|
if loop is not None:
|
||
|
|
self._loop = loop
|
||
|
|
else:
|
||
|
|
self._loop = events.get_event_loop()
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
res = super().__repr__()
|
||
|
|
extra = 'set' if self._value else 'unset'
|
||
|
|
if self._waiters:
|
||
|
|
extra = '{},waiters:{}'.format(extra, len(self._waiters))
|
||
|
|
return '<{} [{}]>'.format(res[1:-1], extra)
|
||
|
|
|
||
|
|
def is_set(self):
|
||
|
|
"""Return True if and only if the internal flag is true."""
|
||
|
|
return self._value
|
||
|
|
|
||
|
|
def set(self):
|
||
|
|
"""Set the internal flag to true. All coroutines waiting for it to
|
||
|
|
become true are awakened. Coroutine that call wait() once the flag is
|
||
|
|
true will not block at all.
|
||
|
|
"""
|
||
|
|
if not self._value:
|
||
|
|
self._value = True
|
||
|
|
|
||
|
|
for fut in self._waiters:
|
||
|
|
if not fut.done():
|
||
|
|
fut.set_result(True)
|
||
|
|
|
||
|
|
def clear(self):
|
||
|
|
"""Reset the internal flag to false. Subsequently, coroutines calling
|
||
|
|
wait() will block until set() is called to set the internal flag
|
||
|
|
to true again."""
|
||
|
|
self._value = False
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def wait(self):
|
||
|
|
"""Block until the internal flag is true.
|
||
|
|
|
||
|
|
If the internal flag is true on entry, return True
|
||
|
|
immediately. Otherwise, block until another coroutine calls
|
||
|
|
set() to set the flag to true, then return True.
|
||
|
|
"""
|
||
|
|
if self._value:
|
||
|
|
return True
|
||
|
|
|
||
|
|
fut = futures.Future(loop=self._loop)
|
||
|
|
self._waiters.append(fut)
|
||
|
|
try:
|
||
|
|
yield from fut
|
||
|
|
return True
|
||
|
|
finally:
|
||
|
|
self._waiters.remove(fut)
|
||
|
|
|
||
|
|
|
||
|
|
class Condition(_ContextManagerMixin):
|
||
|
|
"""Asynchronous equivalent to threading.Condition.
|
||
|
|
|
||
|
|
This class implements condition variable objects. A condition variable
|
||
|
|
allows one or more coroutines to wait until they are notified by another
|
||
|
|
coroutine.
|
||
|
|
|
||
|
|
A new Lock object is created and used as the underlying lock.
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, lock=None, *, loop=None):
|
||
|
|
if loop is not None:
|
||
|
|
self._loop = loop
|
||
|
|
else:
|
||
|
|
self._loop = events.get_event_loop()
|
||
|
|
|
||
|
|
if lock is None:
|
||
|
|
lock = Lock(loop=self._loop)
|
||
|
|
elif lock._loop is not self._loop:
|
||
|
|
raise ValueError("loop argument must agree with lock")
|
||
|
|
|
||
|
|
self._lock = lock
|
||
|
|
# Export the lock's locked(), acquire() and release() methods.
|
||
|
|
self.locked = lock.locked
|
||
|
|
self.acquire = lock.acquire
|
||
|
|
self.release = lock.release
|
||
|
|
|
||
|
|
self._waiters = collections.deque()
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
res = super().__repr__()
|
||
|
|
extra = 'locked' if self.locked() else 'unlocked'
|
||
|
|
if self._waiters:
|
||
|
|
extra = '{},waiters:{}'.format(extra, len(self._waiters))
|
||
|
|
return '<{} [{}]>'.format(res[1:-1], extra)
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def wait(self):
|
||
|
|
"""Wait until notified.
|
||
|
|
|
||
|
|
If the calling coroutine has not acquired the lock when this
|
||
|
|
method is called, a RuntimeError is raised.
|
||
|
|
|
||
|
|
This method releases the underlying lock, and then blocks
|
||
|
|
until it is awakened by a notify() or notify_all() call for
|
||
|
|
the same condition variable in another coroutine. Once
|
||
|
|
awakened, it re-acquires the lock and returns True.
|
||
|
|
"""
|
||
|
|
if not self.locked():
|
||
|
|
raise RuntimeError('cannot wait on un-acquired lock')
|
||
|
|
|
||
|
|
self.release()
|
||
|
|
try:
|
||
|
|
fut = futures.Future(loop=self._loop)
|
||
|
|
self._waiters.append(fut)
|
||
|
|
try:
|
||
|
|
yield from fut
|
||
|
|
return True
|
||
|
|
finally:
|
||
|
|
self._waiters.remove(fut)
|
||
|
|
|
||
|
|
finally:
|
||
|
|
yield from self.acquire()
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def wait_for(self, predicate):
|
||
|
|
"""Wait until a predicate becomes true.
|
||
|
|
|
||
|
|
The predicate should be a callable which result will be
|
||
|
|
interpreted as a boolean value. The final predicate value is
|
||
|
|
the return value.
|
||
|
|
"""
|
||
|
|
result = predicate()
|
||
|
|
while not result:
|
||
|
|
yield from self.wait()
|
||
|
|
result = predicate()
|
||
|
|
return result
|
||
|
|
|
||
|
|
def notify(self, n=1):
|
||
|
|
"""By default, wake up one coroutine waiting on this condition, if any.
|
||
|
|
If the calling coroutine has not acquired the lock when this method
|
||
|
|
is called, a RuntimeError is raised.
|
||
|
|
|
||
|
|
This method wakes up at most n of the coroutines waiting for the
|
||
|
|
condition variable; it is a no-op if no coroutines are waiting.
|
||
|
|
|
||
|
|
Note: an awakened coroutine does not actually return from its
|
||
|
|
wait() call until it can reacquire the lock. Since notify() does
|
||
|
|
not release the lock, its caller should.
|
||
|
|
"""
|
||
|
|
if not self.locked():
|
||
|
|
raise RuntimeError('cannot notify on un-acquired lock')
|
||
|
|
|
||
|
|
idx = 0
|
||
|
|
for fut in self._waiters:
|
||
|
|
if idx >= n:
|
||
|
|
break
|
||
|
|
|
||
|
|
if not fut.done():
|
||
|
|
idx += 1
|
||
|
|
fut.set_result(False)
|
||
|
|
|
||
|
|
def notify_all(self):
|
||
|
|
"""Wake up all threads waiting on this condition. This method acts
|
||
|
|
like notify(), but wakes up all waiting threads instead of one. If the
|
||
|
|
calling thread has not acquired the lock when this method is called,
|
||
|
|
a RuntimeError is raised.
|
||
|
|
"""
|
||
|
|
self.notify(len(self._waiters))
|
||
|
|
|
||
|
|
|
||
|
|
class Semaphore(_ContextManagerMixin):
|
||
|
|
"""A Semaphore implementation.
|
||
|
|
|
||
|
|
A semaphore manages an internal counter which is decremented by each
|
||
|
|
acquire() call and incremented by each release() call. The counter
|
||
|
|
can never go below zero; when acquire() finds that it is zero, it blocks,
|
||
|
|
waiting until some other thread calls release().
|
||
|
|
|
||
|
|
Semaphores also support the context management protocol.
|
||
|
|
|
||
|
|
The optional argument gives the initial value for the internal
|
||
|
|
counter; it defaults to 1. If the value given is less than 0,
|
||
|
|
ValueError is raised.
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, value=1, *, loop=None):
|
||
|
|
if value < 0:
|
||
|
|
raise ValueError("Semaphore initial value must be >= 0")
|
||
|
|
self._value = value
|
||
|
|
self._waiters = collections.deque()
|
||
|
|
if loop is not None:
|
||
|
|
self._loop = loop
|
||
|
|
else:
|
||
|
|
self._loop = events.get_event_loop()
|
||
|
|
|
||
|
|
def __repr__(self):
|
||
|
|
res = super().__repr__()
|
||
|
|
extra = 'locked' if self.locked() else 'unlocked,value:{}'.format(
|
||
|
|
self._value)
|
||
|
|
if self._waiters:
|
||
|
|
extra = '{},waiters:{}'.format(extra, len(self._waiters))
|
||
|
|
return '<{} [{}]>'.format(res[1:-1], extra)
|
||
|
|
|
||
|
|
def locked(self):
|
||
|
|
"""Returns True if semaphore can not be acquired immediately."""
|
||
|
|
return self._value == 0
|
||
|
|
|
||
|
|
@coroutine
|
||
|
|
def acquire(self):
|
||
|
|
"""Acquire a semaphore.
|
||
|
|
|
||
|
|
If the internal counter is larger than zero on entry,
|
||
|
|
decrement it by one and return True immediately. If it is
|
||
|
|
zero on entry, block, waiting until some other coroutine has
|
||
|
|
called release() to make it larger than 0, and then return
|
||
|
|
True.
|
||
|
|
"""
|
||
|
|
if not self._waiters and self._value > 0:
|
||
|
|
self._value -= 1
|
||
|
|
return True
|
||
|
|
|
||
|
|
fut = futures.Future(loop=self._loop)
|
||
|
|
self._waiters.append(fut)
|
||
|
|
try:
|
||
|
|
yield from fut
|
||
|
|
self._value -= 1
|
||
|
|
return True
|
||
|
|
finally:
|
||
|
|
self._waiters.remove(fut)
|
||
|
|
|
||
|
|
def release(self):
|
||
|
|
"""Release a semaphore, incrementing the internal counter by one.
|
||
|
|
When it was zero on entry and another coroutine is waiting for it to
|
||
|
|
become larger than zero again, wake up that coroutine.
|
||
|
|
"""
|
||
|
|
self._value += 1
|
||
|
|
for waiter in self._waiters:
|
||
|
|
if not waiter.done():
|
||
|
|
waiter.set_result(True)
|
||
|
|
break
|
||
|
|
|
||
|
|
|
||
|
|
class BoundedSemaphore(Semaphore):
|
||
|
|
"""A bounded semaphore implementation.
|
||
|
|
|
||
|
|
This raises ValueError in release() if it would increase the value
|
||
|
|
above the initial value.
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, value=1, *, loop=None):
|
||
|
|
self._bound_value = value
|
||
|
|
super().__init__(value, loop=loop)
|
||
|
|
|
||
|
|
def release(self):
|
||
|
|
if self._value >= self._bound_value:
|
||
|
|
raise ValueError('BoundedSemaphore released too many times')
|
||
|
|
super().release()
|