gevent.event
– Notifications of multiple listeners¶Event
¶Bases: gevent.event._AbstractLinkable
A synchronization primitive that allows one greenlet to wake up one or more others.
It has the same interface as threading.Event
but works across greenlets.
An event object manages an internal 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.
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.
isSet
()Return true if and only if the internal flag is true.
is_set
()Return true if and only if the internal flag is true.
ready
()Return true if and only if the internal flag is true.
set
()¶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
wait()
once the flag is true will not block at all
(until clear()
is called).
clear
()¶Reset the internal flag to false.
Subsequently, threads calling wait()
will block until
set()
is called to set the internal flag to true again.
wait
(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 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).
Returns: | 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. |
---|
Changed in version 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.
AsyncResult
¶Bases: gevent.event._AbstractLinkable
A one-time event that stores a value or an exception.
Like Event
it wakes up all the waiters when set()
or set_exception()
is called. Waiters may receive the passed value or exception by calling get()
instead of wait()
. An AsyncResult
instance cannot be reset.
To pass a value call set()
. Calls to 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 set_exception()
. This will cause get()
to raise that exception:
>>> result = AsyncResult()
>>> result.set_exception(RuntimeError('failure'))
>>> result.get()
Traceback (most recent call last):
...
RuntimeError: failure
AsyncResult
implements __call__()
and thus can be used as 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.
Changed in version 1.1: The exact order in which waiting greenlets are awakened is not the same as in 1.0.
Changed in version 1.1: Callbacks linked
to this object are required to be hashable, and duplicates are
merged.
exc_info
¶The three-tuple of exception information if set_exception()
was called.
exception
¶Holds the exception instance passed to set_exception()
if set_exception()
was called.
Otherwise None
.
ready
()¶Return true if and only if it holds a value or an exception
successful
()¶Return true if and only if it is ready and holds a value
set
(value=None)¶Store the value and wake up any waiters.
All greenlets blocking on get()
or wait()
are awakened.
Subsequent calls to wait()
and get()
will not block at all.
set_result
(value=None)¶Store the value and wake up any waiters.
All greenlets blocking on get()
or wait()
are awakened.
Subsequent calls to wait()
and get()
will not block at all.
set_exception
(exception, exc_info=None)¶Store the exception and wake up any waiters.
All greenlets blocking on get()
or wait()
are awakened.
Subsequent calls to wait()
and get()
will not block at all.
Parameters: | exc_info (tuple) – If given, a standard three-tuple of type, value, traceback
as returned by sys.exc_info() . This will be used when the exception
is re-raised to propagate the correct traceback. |
---|
get
(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 immediatelly.
Otherwise, block until another greenlet calls set()
or 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.
Parameters: | block (bool) – If set to False and this instance is not ready,
immediately raise a Timeout exception. |
---|
get_nowait
()¶Return the value or raise the exception without blocking.
If this object is not yet ready
, raise
gevent.Timeout
immediately.
wait
(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 set()
or 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).
result
(timeout=None)¶done
()¶cancel
()¶cancelled
()¶Next page: gevent.queue
– Synchronized queues