432 lines
14 KiB
Python
432 lines
14 KiB
Python
"""Synchronization primitives."""
|
|
|
|
__all__ = ['Lock', 'Event', 'Condition', 'Semaphore']
|
|
|
|
import collections
|
|
|
|
from . import events
|
|
from . import futures
|
|
from . import tasks
|
|
|
|
|
|
class Lock:
|
|
"""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 manager 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
|
|
|
|
@tasks.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.')
|
|
|
|
def __enter__(self):
|
|
if not self._locked:
|
|
raise RuntimeError(
|
|
'"yield from" should be used as context manager expression')
|
|
return True
|
|
|
|
def __exit__(self, *args):
|
|
self.release()
|
|
|
|
def __iter__(self):
|
|
yield from self.acquire()
|
|
return self
|
|
|
|
|
|
class Event:
|
|
"""An Event implementation, our 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
|
|
|
|
@tasks.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:
|
|
"""A Condition implementation, our 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, *, loop=None):
|
|
if loop is not None:
|
|
self._loop = loop
|
|
else:
|
|
self._loop = events.get_event_loop()
|
|
|
|
# Lock as an attribute as in threading.Condition.
|
|
lock = Lock(loop=self._loop)
|
|
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)
|
|
|
|
@tasks.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')
|
|
|
|
keep_lock = True
|
|
self.release()
|
|
try:
|
|
fut = futures.Future(loop=self._loop)
|
|
self._waiters.append(fut)
|
|
try:
|
|
yield from fut
|
|
return True
|
|
finally:
|
|
self._waiters.remove(fut)
|
|
|
|
except GeneratorExit:
|
|
keep_lock = False # Prevent yield in finally clause.
|
|
raise
|
|
finally:
|
|
if keep_lock:
|
|
yield from self.acquire()
|
|
|
|
@tasks.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))
|
|
|
|
def __enter__(self):
|
|
return self._lock.__enter__()
|
|
|
|
def __exit__(self, *args):
|
|
return self._lock.__exit__(*args)
|
|
|
|
def __iter__(self):
|
|
yield from self.acquire()
|
|
return self
|
|
|
|
|
|
class Semaphore:
|
|
"""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 manager protocol.
|
|
|
|
The first 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.
|
|
|
|
The second optional argument determines if the semaphore can be released
|
|
more than initial internal counter value; it defaults to False. If the
|
|
value given is True and number of release() is more than number of
|
|
successful acquire() calls ValueError is raised.
|
|
"""
|
|
|
|
def __init__(self, value=1, bound=False, *, loop=None):
|
|
if value < 0:
|
|
raise ValueError("Semaphore initial value must be > 0")
|
|
self._value = value
|
|
self._bound = bound
|
|
self._bound_value = value
|
|
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,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._locked
|
|
|
|
@tasks.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
|
|
if self._value == 0:
|
|
self._locked = True
|
|
return True
|
|
|
|
fut = futures.Future(loop=self._loop)
|
|
self._waiters.append(fut)
|
|
try:
|
|
yield from fut
|
|
self._value -= 1
|
|
if self._value == 0:
|
|
self._locked = True
|
|
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.
|
|
|
|
If Semaphore is created with "bound" parameter equals true, then
|
|
release() method checks to make sure its current value doesn't exceed
|
|
its initial value. If it does, ValueError is raised.
|
|
"""
|
|
if self._bound and self._value >= self._bound_value:
|
|
raise ValueError('Semaphore released too many times')
|
|
|
|
self._value += 1
|
|
self._locked = False
|
|
|
|
for waiter in self._waiters:
|
|
if not waiter.done():
|
|
waiter.set_result(True)
|
|
break
|
|
|
|
def __enter__(self):
|
|
# TODO: This is questionable. How do we know the user actually
|
|
# wrote "with (yield from sema)" instead of "with sema"?
|
|
return True
|
|
|
|
def __exit__(self, *args):
|
|
self.release()
|
|
|
|
def __iter__(self):
|
|
yield from self.acquire()
|
|
return self
|