Source code for gevent.event

# Copyright (c) 2009-2016 Denis Bilenko, gevent contributors. See LICENSE for details.
# cython: auto_pickle=False,embedsignature=True,always_allow_keywords=False,infer_types=True

"""Basic synchronization primitives: Event and AsyncResult"""
from __future__ import print_function

from gevent._util import _NONE
from gevent._compat import reraise
from gevent._tblib import dump_traceback, load_traceback

from gevent.timeout import Timeout


__all__ = [
    'Event',
    'AsyncResult',
]

def _get_linkable():
    x = __import__('gevent._abstract_linkable')
    return x._abstract_linkable.AbstractLinkable
locals()['AbstractLinkable'] = _get_linkable()
del _get_linkable

# Sadly, something about the way we have to "import" AbstractLinkable
# breaks pylint's inference of slots, even though they're declared
# right here.
# pylint:disable=assigning-non-slot

[docs]class Event(AbstractLinkable): # pylint:disable=undefined-variable """A synchronization primitive that allows one greenlet to wake up one or more others. It has the same interface as :class:`threading.Event` but works across greenlets. An event object manages an internal flag that can be set to true with the :meth:`set` method and reset to false with the :meth:`clear` method. The :meth:`wait` method blocks until the flag is true. .. note:: The order and timing in which waiting greenlets are awakened is not determined. As an implementation note, in gevent 1.1 and 1.0, waiting greenlets are awakened in a undetermined order sometime *after* the current greenlet yields to the event loop. Other greenlets (those not waiting to be awakened) may run between the current greenlet yielding and the waiting greenlets being awakened. These details may change in the future. """ __slots__ = ('_flag',) def __init__(self): super(Event, self).__init__() self._flag = False def __str__(self): return '<%s %s _links[%s]>' % (self.__class__.__name__, (self._flag and 'set') or 'clear', self.linkcount())
[docs] def is_set(self): """Return true if and only if the internal flag is true.""" return self._flag
[docs] def isSet(self): # makes it a better drop-in replacement for threading.Event return self._flag
[docs] def ready(self): # makes it compatible with AsyncResult and Greenlet (for # example in wait()) return self._flag
[docs] def set(self): """ Set the internal flag to true. All greenlets waiting for it to become true are awakened in some order at some time in the future. Greenlets that call :meth:`wait` once the flag is true will not block at all (until :meth:`clear` is called). """ self._flag = True self._check_and_notify()
[docs] def clear(self): """ Reset the internal flag to false. Subsequently, threads calling :meth:`wait` will block until :meth:`set` is called to set the internal flag to true again. """ self._flag = False
def _wait_return_value(self, waited, wait_success): # To avoid the race condition outlined in http://bugs.python.org/issue13502, # if we had to wait, then we need to return whether or not # the condition got changed. Otherwise we simply echo # the current state of the flag (which should be true) if not waited: flag = self._flag assert flag, "if we didn't wait we should already be set" return flag return wait_success
[docs] def wait(self, timeout=None): """ Block until the internal flag is true. If the internal flag is true on entry, return immediately. Otherwise, block until another thread (greenlet) calls :meth:`set` to set the flag to true, or until the optional timeout occurs. When the *timeout* argument is present and not ``None``, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof). :return: This method returns true if and only if the internal flag has been set to true, either before the wait call or after the wait starts, so it will always return ``True`` except if a timeout is given and the operation times out. .. versionchanged:: 1.1 The return value represents the flag during the elapsed wait, not just after it elapses. This solves a race condition if one greenlet sets and then clears the flag without switching, while other greenlets are waiting. When the waiters wake up, this will return True; previously, they would still wake up, but the return value would be False. This is most noticeable when the *timeout* is present. """ return self._wait(timeout)
def _reset_internal_locks(self): # pragma: no cover # for compatibility with threading.Event # Exception AttributeError: AttributeError("'Event' object has no attribute '_reset_internal_locks'",) # in <module 'threading' from '/usr/lib/python2.7/threading.pyc'> ignored pass
[docs]class AsyncResult(AbstractLinkable): # pylint:disable=undefined-variable """A one-time event that stores a value or an exception. Like :class:`Event` it wakes up all the waiters when :meth:`set` or :meth:`set_exception` is called. Waiters may receive the passed value or exception by calling :meth:`get` instead of :meth:`wait`. An :class:`AsyncResult` instance cannot be reset. To pass a value call :meth:`set`. Calls to :meth:`get` (those that are currently blocking as well as those made in the future) will return the value: >>> result = AsyncResult() >>> result.set(100) >>> result.get() 100 To pass an exception call :meth:`set_exception`. This will cause :meth:`get` to raise that exception: >>> result = AsyncResult() >>> result.set_exception(RuntimeError('failure')) >>> result.get() Traceback (most recent call last): ... RuntimeError: failure :class:`AsyncResult` implements :meth:`__call__` and thus can be used as :meth:`link` target: >>> import gevent >>> result = AsyncResult() >>> gevent.spawn(lambda : 1/0).link(result) >>> try: ... result.get() ... except ZeroDivisionError: ... print('ZeroDivisionError') ZeroDivisionError .. note:: The order and timing in which waiting greenlets are awakened is not determined. As an implementation note, in gevent 1.1 and 1.0, waiting greenlets are awakened in a undetermined order sometime *after* the current greenlet yields to the event loop. Other greenlets (those not waiting to be awakened) may run between the current greenlet yielding and the waiting greenlets being awakened. These details may change in the future. .. versionchanged:: 1.1 The exact order in which waiting greenlets are awakened is not the same as in 1.0. .. versionchanged:: 1.1 Callbacks :meth:`linked <rawlink>` to this object are required to be hashable, and duplicates are merged. """ __slots__ = ('_value', '_exc_info', '_imap_task_index') def __init__(self): super(AsyncResult, self).__init__() self._value = _NONE self._exc_info = () @property def _exception(self): return self._exc_info[1] if self._exc_info else _NONE @property def value(self): """ Holds the value passed to :meth:`set` if :meth:`set` was called. Otherwise, ``None`` """ return self._value if self._value is not _NONE else None @property def exc_info(self): """ The three-tuple of exception information if :meth:`set_exception` was called. """ if self._exc_info: return (self._exc_info[0], self._exc_info[1], load_traceback(self._exc_info[2])) return () def __str__(self): result = '<%s ' % (self.__class__.__name__, ) if self.value is not None or self._exception is not _NONE: result += 'value=%r ' % self.value if self._exception is not None and self._exception is not _NONE: result += 'exception=%r ' % self._exception if self._exception is _NONE: result += 'unset ' return result + ' _links[%s]>' % self.linkcount()
[docs] def ready(self): """Return true if and only if it holds a value or an exception""" return self._exc_info or self._value is not _NONE
[docs] def successful(self): """Return true if and only if it is ready and holds a value""" return self._value is not _NONE
@property def exception(self): """Holds the exception instance passed to :meth:`set_exception` if :meth:`set_exception` was called. Otherwise ``None``.""" if self._exc_info: return self._exc_info[1]
[docs] def set(self, value=None): """Store the value and wake up any waiters. All greenlets blocking on :meth:`get` or :meth:`wait` are awakened. Subsequent calls to :meth:`wait` and :meth:`get` will not block at all. """ self._value = value self._check_and_notify()
[docs] def set_exception(self, exception, exc_info=None): """Store the exception and wake up any waiters. All greenlets blocking on :meth:`get` or :meth:`wait` are awakened. Subsequent calls to :meth:`wait` and :meth:`get` will not block at all. :keyword tuple exc_info: If given, a standard three-tuple of type, value, :class:`traceback` as returned by :func:`sys.exc_info`. This will be used when the exception is re-raised to propagate the correct traceback. """ if exc_info: self._exc_info = (exc_info[0], exc_info[1], dump_traceback(exc_info[2])) else: self._exc_info = (type(exception), exception, dump_traceback(None)) self._check_and_notify()
def _raise_exception(self): reraise(*self.exc_info)
[docs] def get(self, block=True, timeout=None): """Return the stored value or raise the exception. If this instance already holds a value or an exception, return or raise it immediately. Otherwise, block until another greenlet calls :meth:`set` or :meth:`set_exception` or until the optional timeout occurs. When the *timeout* argument is present and not ``None``, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof). If the *timeout* elapses, the *Timeout* exception will be raised. :keyword bool block: If set to ``False`` and this instance is not ready, immediately raise a :class:`Timeout` exception. """ if self._value is not _NONE: return self._value if self._exc_info: return self._raise_exception() if not block: # Not ready and not blocking, so immediately timeout raise Timeout() # Wait, raising a timeout that elapses self._wait_core(timeout, ()) # by definition we are now ready return self.get(block=False)
[docs] def get_nowait(self): """ Return the value or raise the exception without blocking. If this object is not yet :meth:`ready <ready>`, raise :class:`gevent.Timeout` immediately. """ return self.get(block=False)
def _wait_return_value(self, waited, wait_success): # pylint:disable=unused-argument # Always return the value. Since this is a one-shot event, # no race condition should reset it. return self.value
[docs] def wait(self, timeout=None): """Block until the instance is ready. If this instance already holds a value, it is returned immediately. If this instance already holds an exception, ``None`` is returned immediately. Otherwise, block until another greenlet calls :meth:`set` or :meth:`set_exception` (at which point either the value or ``None`` will be returned, respectively), or until the optional timeout expires (at which point ``None`` will also be returned). When the *timeout* argument is present and not ``None``, it should be a floating point number specifying a timeout for the operation in seconds (or fractions thereof). .. note:: If a timeout is given and expires, ``None`` will be returned (no timeout exception will be raised). """ return self._wait(timeout)
# link protocol def __call__(self, source): if source.successful(): self.set(source.value) else: self.set_exception(source.exception, getattr(source, 'exc_info', None)) # Methods to make us more like concurrent.futures.Future
[docs] def result(self, timeout=None): return self.get(timeout=timeout)
set_result = set
[docs] def done(self): return self.ready()
# we don't support cancelling
[docs] def cancel(self): return False
[docs] def cancelled(self): return False
# exception is a method, we use it as a property from gevent._util import import_c_accel import_c_accel(globals(), 'gevent._event')