mirror of
https://github.com/python/cpython.git
synced 2025-10-31 13:41:24 +00:00
c38a0002bc
svn+ssh://pythondev@svn.python.org/python/trunk ........ r72932 | georg.brandl | 2009-05-26 09:50:23 +0200 (Di, 26 Mai 2009) | 1 line #6112: list.remove raises ValueError, not RuntimeError. ........
131 lines
4.4 KiB
ReStructuredText
131 lines
4.4 KiB
ReStructuredText
:mod:`sched` --- Event scheduler
|
|
================================
|
|
|
|
.. module:: sched
|
|
:synopsis: General purpose event scheduler.
|
|
.. sectionauthor:: Moshe Zadka <moshez@zadka.site.co.il>
|
|
|
|
.. index:: single: event scheduling
|
|
|
|
The :mod:`sched` module defines a class which implements a general purpose event
|
|
scheduler:
|
|
|
|
|
|
.. class:: scheduler(timefunc, delayfunc)
|
|
|
|
The :class:`scheduler` class defines a generic interface to scheduling events.
|
|
It needs two functions to actually deal with the "outside world" --- *timefunc*
|
|
should be callable without arguments, and return a number (the "time", in any
|
|
units whatsoever). The *delayfunc* function should be callable with one
|
|
argument, compatible with the output of *timefunc*, and should delay that many
|
|
time units. *delayfunc* will also be called with the argument ``0`` after each
|
|
event is run to allow other threads an opportunity to run in multi-threaded
|
|
applications.
|
|
|
|
Example::
|
|
|
|
>>> import sched, time
|
|
>>> s = sched.scheduler(time.time, time.sleep)
|
|
>>> def print_time(): print("From print_time", time.time())
|
|
...
|
|
>>> def print_some_times():
|
|
... print(time.time())
|
|
... s.enter(5, 1, print_time, ())
|
|
... s.enter(10, 1, print_time, ())
|
|
... s.run()
|
|
... print(time.time())
|
|
...
|
|
>>> print_some_times()
|
|
930343690.257
|
|
From print_time 930343695.274
|
|
From print_time 930343700.273
|
|
930343700.276
|
|
|
|
In multi-threaded environments, the :class:`scheduler` class has limitations
|
|
with respect to thread-safety, inability to insert a new task before
|
|
the one currently pending in a running scheduler, and holding up the main
|
|
thread until the event queue is empty. Instead, the preferred approach
|
|
is to use the :class:`threading.Timer` class instead.
|
|
|
|
Example::
|
|
|
|
>>> import time
|
|
>>> from threading import Timer
|
|
>>> def print_time():
|
|
... print("From print_time", time.time())
|
|
...
|
|
>>> def print_some_times():
|
|
... print(time.time())
|
|
... Timer(5, print_time, ()).start()
|
|
... Timer(10, print_time, ()).start()
|
|
... time.sleep(11) # sleep while time-delay events execute
|
|
... print(time.time())
|
|
...
|
|
>>> print_some_times()
|
|
930343690.257
|
|
From print_time 930343695.274
|
|
From print_time 930343700.273
|
|
930343701.301
|
|
|
|
|
|
.. _scheduler-objects:
|
|
|
|
Scheduler Objects
|
|
-----------------
|
|
|
|
:class:`scheduler` instances have the following methods and attributes:
|
|
|
|
|
|
.. method:: scheduler.enterabs(time, priority, action, argument)
|
|
|
|
Schedule a new event. The *time* argument should be a numeric type compatible
|
|
with the return value of the *timefunc* function passed to the constructor.
|
|
Events scheduled for the same *time* will be executed in the order of their
|
|
*priority*.
|
|
|
|
Executing the event means executing ``action(*argument)``. *argument* must be a
|
|
sequence holding the parameters for *action*.
|
|
|
|
Return value is an event which may be used for later cancellation of the event
|
|
(see :meth:`cancel`).
|
|
|
|
|
|
.. method:: scheduler.enter(delay, priority, action, argument)
|
|
|
|
Schedule an event for *delay* more time units. Other then the relative time, the
|
|
other arguments, the effect and the return value are the same as those for
|
|
:meth:`enterabs`.
|
|
|
|
|
|
.. method:: scheduler.cancel(event)
|
|
|
|
Remove the event from the queue. If *event* is not an event currently in the
|
|
queue, this method will raise a :exc:`ValueError`.
|
|
|
|
|
|
.. method:: scheduler.empty()
|
|
|
|
Return true if the event queue is empty.
|
|
|
|
|
|
.. method:: scheduler.run()
|
|
|
|
Run all scheduled events. This function will wait (using the :func:`delayfunc`
|
|
function passed to the constructor) for the next event, then execute it and so
|
|
on until there are no more scheduled events.
|
|
|
|
Either *action* or *delayfunc* can raise an exception. In either case, the
|
|
scheduler will maintain a consistent state and propagate the exception. If an
|
|
exception is raised by *action*, the event will not be attempted in future calls
|
|
to :meth:`run`.
|
|
|
|
If a sequence of events takes longer to run than the time available before the
|
|
next event, the scheduler will simply fall behind. No events will be dropped;
|
|
the calling code is responsible for canceling events which are no longer
|
|
pertinent.
|
|
|
|
.. attribute:: scheduler.queue
|
|
|
|
Read-only attribute returning a list of upcoming events in the order they
|
|
will be run. Each event is shown as a :term:`named tuple` with the
|
|
following fields: time, priority, action, argument.
|