| """Synchronization primitives.""" |
| |
| __all__ = ('Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore') |
| |
| import collections |
| import warnings |
| |
| from . import events |
| from . import exceptions |
| |
| |
| class _ContextManagerMixin: |
| async def __aenter__(self): |
| await self.acquire() |
| # We have no use for the "as ..." clause in the with |
| # statement for locks. |
| return None |
| |
| async 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 'await'. |
| |
| Locks also support the asynchronous context management protocol. |
| 'async with lock' statement should be used. |
| |
| Usage: |
| |
| lock = Lock() |
| ... |
| await lock.acquire() |
| try: |
| ... |
| finally: |
| lock.release() |
| |
| Context manager usage: |
| |
| lock = Lock() |
| ... |
| async with lock: |
| ... |
| |
| Lock objects can be tested for locking state: |
| |
| if not lock.locked(): |
| await lock.acquire() |
| else: |
| # lock is acquired |
| ... |
| |
| """ |
| |
| def __init__(self, *, loop=None): |
| self._waiters = None |
| self._locked = False |
| if loop is None: |
| self._loop = events.get_event_loop() |
| else: |
| self._loop = loop |
| warnings.warn("The loop argument is deprecated since Python 3.8, " |
| "and scheduled for removal in Python 3.10.", |
| DeprecationWarning, stacklevel=2) |
| |
| def __repr__(self): |
| res = super().__repr__() |
| extra = 'locked' if self._locked else 'unlocked' |
| if self._waiters: |
| extra = f'{extra}, waiters:{len(self._waiters)}' |
| return f'<{res[1:-1]} [{extra}]>' |
| |
| def locked(self): |
| """Return True if lock is acquired.""" |
| return self._locked |
| |
| async 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._locked and (self._waiters is None or |
| all(w.cancelled() for w in self._waiters))): |
| self._locked = True |
| return True |
| |
| if self._waiters is None: |
| self._waiters = collections.deque() |
| fut = self._loop.create_future() |
| self._waiters.append(fut) |
| |
| # Finally block should be called before the CancelledError |
| # handling as we don't want CancelledError to call |
| # _wake_up_first() and attempt to wake up itself. |
| try: |
| try: |
| await fut |
| finally: |
| self._waiters.remove(fut) |
| except exceptions.CancelledError: |
| if not self._locked: |
| self._wake_up_first() |
| raise |
| |
| self._locked = True |
| return True |
| |
| 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 |
| self._wake_up_first() |
| else: |
| raise RuntimeError('Lock is not acquired.') |
| |
| def _wake_up_first(self): |
| """Wake up the first waiter if it isn't done.""" |
| if not self._waiters: |
| return |
| try: |
| fut = next(iter(self._waiters)) |
| except StopIteration: |
| return |
| |
| # .done() necessarily means that a waiter will wake up later on and |
| # either take the lock, or, if it was cancelled and lock wasn't |
| # taken already, will hit this again and wake up a new waiter. |
| if not fut.done(): |
| fut.set_result(True) |
| |
| |
| 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 None: |
| self._loop = events.get_event_loop() |
| else: |
| self._loop = loop |
| warnings.warn("The loop argument is deprecated since Python 3.8, " |
| "and scheduled for removal in Python 3.10.", |
| DeprecationWarning, stacklevel=2) |
| |
| def __repr__(self): |
| res = super().__repr__() |
| extra = 'set' if self._value else 'unset' |
| if self._waiters: |
| extra = f'{extra}, waiters:{len(self._waiters)}' |
| return f'<{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 |
| |
| async 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 = self._loop.create_future() |
| self._waiters.append(fut) |
| try: |
| await 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 None: |
| self._loop = events.get_event_loop() |
| else: |
| self._loop = loop |
| warnings.warn("The loop argument is deprecated since Python 3.8, " |
| "and scheduled for removal in Python 3.10.", |
| DeprecationWarning, stacklevel=2) |
| |
| if lock is None: |
| lock = Lock(loop=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 = f'{extra}, waiters:{len(self._waiters)}' |
| return f'<{res[1:-1]} [{extra}]>' |
| |
| async 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 = self._loop.create_future() |
| self._waiters.append(fut) |
| try: |
| await fut |
| return True |
| finally: |
| self._waiters.remove(fut) |
| |
| finally: |
| # Must reacquire lock even if wait is cancelled |
| cancelled = False |
| while True: |
| try: |
| await self.acquire() |
| break |
| except exceptions.CancelledError: |
| cancelled = True |
| |
| if cancelled: |
| raise exceptions.CancelledError |
| |
| async 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: |
| await 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 None: |
| self._loop = events.get_event_loop() |
| else: |
| self._loop = loop |
| warnings.warn("The loop argument is deprecated since Python 3.8, " |
| "and scheduled for removal in Python 3.10.", |
| DeprecationWarning, stacklevel=2) |
| |
| def __repr__(self): |
| res = super().__repr__() |
| extra = 'locked' if self.locked() else f'unlocked, value:{self._value}' |
| if self._waiters: |
| extra = f'{extra}, waiters:{len(self._waiters)}' |
| return f'<{res[1:-1]} [{extra}]>' |
| |
| def _wake_up_next(self): |
| while self._waiters: |
| waiter = self._waiters.popleft() |
| if not waiter.done(): |
| waiter.set_result(None) |
| return |
| |
| def locked(self): |
| """Returns True if semaphore can not be acquired immediately.""" |
| return self._value == 0 |
| |
| async 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. |
| """ |
| while self._value <= 0: |
| fut = self._loop.create_future() |
| self._waiters.append(fut) |
| try: |
| await fut |
| except: |
| # See the similar code in Queue.get. |
| fut.cancel() |
| if self._value > 0 and not fut.cancelled(): |
| self._wake_up_next() |
| raise |
| self._value -= 1 |
| return True |
| |
| 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 |
| self._wake_up_next() |
| |
| |
| 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): |
| if loop: |
| warnings.warn("The loop argument is deprecated since Python 3.8, " |
| "and scheduled for removal in Python 3.10.", |
| DeprecationWarning, stacklevel=2) |
| |
| 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() |
