/Windows/Python3.8/WPy64-3830/WPy64-3830/python-3.8.3.amd64/Lib/asyncio/locks.py

"""Synchronization primitives."""



__all__ = ('Lock', 'Event', 'Condition', 'Semaphore', 'BoundedSemaphore')



import collections

import types

import warnings



from . import events

from . import futures

from . import exceptions

from .import coroutines





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>



    Deprecated, use 'async with' statement:

        async 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



    @types.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()

        # Deprecated, use 'async with' statement:

        #     async with lock:

        #         <block>

        warnings.warn("'with (yield from lock)' is deprecated "

                      "use 'async with lock' instead",

                      DeprecationWarning, stacklevel=2)

        yield from self.acquire()

        return _ContextManager(self)



    # The flag is needed for legacy asyncio.iscoroutine()

    __iter__._is_coroutine = coroutines._is_coroutine



    async def __acquire_ctx(self):

        await self.acquire()

        return _ContextManager(self)



    def __await__(self):

        warnings.warn("'with await lock' is deprecated "

                      "use 'async with lock' instead",

                      DeprecationWarning, stacklevel=2)

        # To make "with await lock" work.

        return self.__acquire_ctx().__await__()



    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()