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# Copyright 2015 The Tornado Authors
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
import collections
from concurrent.futures import CancelledError
import datetime
import types
from tornado import gen, ioloop
from tornado.concurrent import Future, future_set_result_unless_cancelled
from typing import Union, Optional, Type, Any, Awaitable
import typing
if typing.TYPE_CHECKING:
from typing import Deque, Set # noqa: F401
__all__ = ["Condition", "Event", "Semaphore", "BoundedSemaphore", "Lock"]
class _TimeoutGarbageCollector(object):
"""Base class for objects that periodically clean up timed-out waiters.
Avoids memory leak in a common pattern like:
while True:
yield condition.wait(short_timeout)
print('looping....')
"""
def __init__(self) -> None:
self._waiters = collections.deque() # type: Deque[Future]
self._timeouts = 0
def _garbage_collect(self) -> None:
# Occasionally clear timed-out waiters.
self._timeouts += 1
if self._timeouts > 100:
self._timeouts = 0
self._waiters = collections.deque(w for w in self._waiters if not w.done())
class Condition(_TimeoutGarbageCollector):
"""A condition allows one or more coroutines to wait until notified.
Like a standard `threading.Condition`, but does not need an underlying lock
that is acquired and released.
With a `Condition`, coroutines can wait to be notified by other coroutines:
.. testcode::
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.locks import Condition
condition = Condition()
async def waiter():
print("I'll wait right here")
await condition.wait()
print("I'm done waiting")
async def notifier():
print("About to notify")
condition.notify()
print("Done notifying")
async def runner():
# Wait for waiter() and notifier() in parallel
await gen.multi([waiter(), notifier()])
IOLoop.current().run_sync(runner)
.. testoutput::
I'll wait right here
About to notify
Done notifying
I'm done waiting
`wait` takes an optional ``timeout`` argument, which is either an absolute
timestamp::
io_loop = IOLoop.current()
# Wait up to 1 second for a notification.
await condition.wait(timeout=io_loop.time() + 1)
...or a `datetime.timedelta` for a timeout relative to the current time::
# Wait up to 1 second.
await condition.wait(timeout=datetime.timedelta(seconds=1))
The method returns False if there's no notification before the deadline.
.. versionchanged:: 5.0
Previously, waiters could be notified synchronously from within
`notify`. Now, the notification will always be received on the
next iteration of the `.IOLoop`.
"""
def __init__(self) -> None:
super(Condition, self).__init__()
self.io_loop = ioloop.IOLoop.current()
def __repr__(self) -> str:
result = "<%s" % (self.__class__.__name__,)
if self._waiters:
result += " waiters[%s]" % len(self._waiters)
return result + ">"
def wait(self, timeout: Union[float, datetime.timedelta] = None) -> Awaitable[bool]:
"""Wait for `.notify`.
Returns a `.Future` that resolves ``True`` if the condition is notified,
or ``False`` after a timeout.
"""
waiter = Future() # type: Future[bool]
self._waiters.append(waiter)
if timeout:
def on_timeout() -> None:
if not waiter.done():
future_set_result_unless_cancelled(waiter, False)
self._garbage_collect()
io_loop = ioloop.IOLoop.current()
timeout_handle = io_loop.add_timeout(timeout, on_timeout)
waiter.add_done_callback(lambda _: io_loop.remove_timeout(timeout_handle))
return waiter
def notify(self, n: int = 1) -> None:
"""Wake ``n`` waiters."""
waiters = [] # Waiters we plan to run right now.
while n and self._waiters:
waiter = self._waiters.popleft()
if not waiter.done(): # Might have timed out.
n -= 1
waiters.append(waiter)
for waiter in waiters:
future_set_result_unless_cancelled(waiter, True)
def notify_all(self) -> None:
"""Wake all waiters."""
self.notify(len(self._waiters))
class Event(object):
"""An event blocks coroutines until its internal flag is set to True.
Similar to `threading.Event`.
A coroutine can wait for an event to be set. Once it is set, calls to
``yield event.wait()`` will not block unless the event has been cleared:
.. testcode::
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.locks import Event
event = Event()
async def waiter():
print("Waiting for event")
await event.wait()
print("Not waiting this time")
await event.wait()
print("Done")
async def setter():
print("About to set the event")
event.set()
async def runner():
await gen.multi([waiter(), setter()])
IOLoop.current().run_sync(runner)
.. testoutput::
Waiting for event
About to set the event
Not waiting this time
Done
"""
def __init__(self) -> None:
self._value = False
self._waiters = set() # type: Set[Future[None]]
def __repr__(self) -> str:
return "<%s %s>" % (
self.__class__.__name__,
"set" if self.is_set() else "clear",
)
def is_set(self) -> bool:
"""Return ``True`` if the internal flag is true."""
return self._value
def set(self) -> None:
"""Set the internal flag to ``True``. All waiters are awakened.
Calling `.wait` once the flag is set will not block.
"""
if not self._value:
self._value = True
for fut in self._waiters:
if not fut.done():
fut.set_result(None)
def clear(self) -> None:
"""Reset the internal flag to ``False``.
Calls to `.wait` will block until `.set` is called.
"""
self._value = False
def wait(self, timeout: Union[float, datetime.timedelta] = None) -> Awaitable[None]:
"""Block until the internal flag is true.
Returns an awaitable, which raises `tornado.util.TimeoutError` after a
timeout.
"""
fut = Future() # type: Future[None]
if self._value:
fut.set_result(None)
return fut
self._waiters.add(fut)
fut.add_done_callback(lambda fut: self._waiters.remove(fut))
if timeout is None:
return fut
else:
timeout_fut = gen.with_timeout(
timeout, fut, quiet_exceptions=(CancelledError,)
)
# This is a slightly clumsy workaround for the fact that
# gen.with_timeout doesn't cancel its futures. Cancelling
# fut will remove it from the waiters list.
timeout_fut.add_done_callback(
lambda tf: fut.cancel() if not fut.done() else None
)
return timeout_fut
class _ReleasingContextManager(object):
"""Releases a Lock or Semaphore at the end of a "with" statement.
with (yield semaphore.acquire()):
pass
# Now semaphore.release() has been called.
"""
def __init__(self, obj: Any) -> None:
self._obj = obj
def __enter__(self) -> None:
pass
def __exit__(
self,
exc_type: "Optional[Type[BaseException]]",
exc_val: Optional[BaseException],
exc_tb: Optional[types.TracebackType],
) -> None:
self._obj.release()
class Semaphore(_TimeoutGarbageCollector):
"""A lock that can be acquired a fixed number of times before blocking.
A Semaphore manages a counter representing the number of `.release` calls
minus the number of `.acquire` calls, plus an initial value. The `.acquire`
method blocks if necessary until it can return without making the counter
negative.
Semaphores limit access to a shared resource. To allow access for two
workers at a time:
.. testsetup:: semaphore
from collections import deque
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.concurrent import Future
# Ensure reliable doctest output: resolve Futures one at a time.
futures_q = deque([Future() for _ in range(3)])
async def simulator(futures):
for f in futures:
# simulate the asynchronous passage of time
await gen.sleep(0)
await gen.sleep(0)
f.set_result(None)
IOLoop.current().add_callback(simulator, list(futures_q))
def use_some_resource():
return futures_q.popleft()
.. testcode:: semaphore
from tornado import gen
from tornado.ioloop import IOLoop
from tornado.locks import Semaphore
sem = Semaphore(2)
async def worker(worker_id):
await sem.acquire()
try:
print("Worker %d is working" % worker_id)
await use_some_resource()
finally:
print("Worker %d is done" % worker_id)
sem.release()
async def runner():
# Join all workers.
await gen.multi([worker(i) for i in range(3)])
IOLoop.current().run_sync(runner)
.. testoutput:: semaphore
Worker 0 is working
Worker 1 is working
Worker 0 is done
Worker 2 is working
Worker 1 is done
Worker 2 is done
Workers 0 and 1 are allowed to run concurrently, but worker 2 waits until
the semaphore has been released once, by worker 0.
The semaphore can be used as an async context manager::
async def worker(worker_id):
async with sem:
print("Worker %d is working" % worker_id)
await use_some_resource()
# Now the semaphore has been released.
print("Worker %d is done" % worker_id)
For compatibility with older versions of Python, `.acquire` is a
context manager, so ``worker`` could also be written as::
@gen.coroutine
def worker(worker_id):
with (yield sem.acquire()):
print("Worker %d is working" % worker_id)
yield use_some_resource()
# Now the semaphore has been released.
print("Worker %d is done" % worker_id)
.. versionchanged:: 4.3
Added ``async with`` support in Python 3.5.
"""
def __init__(self, value: int = 1) -> None:
super(Semaphore, self).__init__()
if value < 0:
raise ValueError("semaphore initial value must be >= 0")
self._value = value
def __repr__(self) -> str:
res = super(Semaphore, self).__repr__()
extra = (
"locked" if self._value == 0 else "unlocked,value:{0}".format(self._value)
)
if self._waiters:
extra = "{0},waiters:{1}".format(extra, len(self._waiters))
return "<{0} [{1}]>".format(res[1:-1], extra)
def release(self) -> None:
"""Increment the counter and wake one waiter."""
self._value += 1
while self._waiters:
waiter = self._waiters.popleft()
if not waiter.done():
self._value -= 1
# If the waiter is a coroutine paused at
#
# with (yield semaphore.acquire()):
#
# then the context manager's __exit__ calls release() at the end
# of the "with" block.
waiter.set_result(_ReleasingContextManager(self))
break
def acquire(
self, timeout: Union[float, datetime.timedelta] = None
) -> Awaitable[_ReleasingContextManager]:
"""Decrement the counter. Returns an awaitable.
Block if the counter is zero and wait for a `.release`. The awaitable
raises `.TimeoutError` after the deadline.
"""
waiter = Future() # type: Future[_ReleasingContextManager]
if self._value > 0:
self._value -= 1
waiter.set_result(_ReleasingContextManager(self))
else:
self._waiters.append(waiter)
if timeout:
def on_timeout() -> None:
if not waiter.done():
waiter.set_exception(gen.TimeoutError())
self._garbage_collect()
io_loop = ioloop.IOLoop.current()
timeout_handle = io_loop.add_timeout(timeout, on_timeout)
waiter.add_done_callback(
lambda _: io_loop.remove_timeout(timeout_handle)
)
return waiter
def __enter__(self) -> None:
raise RuntimeError("Use 'async with' instead of 'with' for Semaphore")
def __exit__(
self,
typ: "Optional[Type[BaseException]]",
value: Optional[BaseException],
traceback: Optional[types.TracebackType],
) -> None:
self.__enter__()
async def __aenter__(self) -> None:
await self.acquire()
async def __aexit__(
self,
typ: "Optional[Type[BaseException]]",
value: Optional[BaseException],
tb: Optional[types.TracebackType],
) -> None:
self.release()
class BoundedSemaphore(Semaphore):
"""A semaphore that prevents release() being called too many times.
If `.release` would increment the semaphore's value past the initial
value, it raises `ValueError`. Semaphores are mostly used to guard
resources with limited capacity, so a semaphore released too many times
is a sign of a bug.
"""
def __init__(self, value: int = 1) -> None:
super(BoundedSemaphore, self).__init__(value=value)
self._initial_value = value
def release(self) -> None:
"""Increment the counter and wake one waiter."""
if self._value >= self._initial_value:
raise ValueError("Semaphore released too many times")
super(BoundedSemaphore, self).release()
class Lock(object):
"""A lock for coroutines.
A Lock begins unlocked, and `acquire` locks it immediately. While it is
locked, a coroutine that yields `acquire` waits until another coroutine
calls `release`.
Releasing an unlocked lock raises `RuntimeError`.
A Lock can be used as an async context manager with the ``async
with`` statement:
>>> from tornado import locks
>>> lock = locks.Lock()
>>>
>>> async def f():
... async with lock:
... # Do something holding the lock.
... pass
...
... # Now the lock is released.
For compatibility with older versions of Python, the `.acquire`
method asynchronously returns a regular context manager:
>>> async def f2():
... with (yield lock.acquire()):
... # Do something holding the lock.
... pass
...
... # Now the lock is released.
.. versionchanged:: 4.3
Added ``async with`` support in Python 3.5.
"""
def __init__(self) -> None:
self._block = BoundedSemaphore(value=1)
def __repr__(self) -> str:
return "<%s _block=%s>" % (self.__class__.__name__, self._block)
def acquire(
self, timeout: Union[float, datetime.timedelta] = None
) -> Awaitable[_ReleasingContextManager]:
"""Attempt to lock. Returns an awaitable.
Returns an awaitable, which raises `tornado.util.TimeoutError` after a
timeout.
"""
return self._block.acquire(timeout)
def release(self) -> None:
"""Unlock.
The first coroutine in line waiting for `acquire` gets the lock.
If not locked, raise a `RuntimeError`.
"""
try:
self._block.release()
except ValueError:
raise RuntimeError("release unlocked lock")
def __enter__(self) -> None:
raise RuntimeError("Use `async with` instead of `with` for Lock")
def __exit__(
self,
typ: "Optional[Type[BaseException]]",
value: Optional[BaseException],
tb: Optional[types.TracebackType],
) -> None:
self.__enter__()
async def __aenter__(self) -> None:
await self.acquire()
async def __aexit__(
self,
typ: "Optional[Type[BaseException]]",
value: Optional[BaseException],
tb: Optional[types.TracebackType],
) -> None:
self.release()