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Paul McCarthy authoredone instance, if two or more threads accessed a method at the same time.
idle.py 29.37 KiB
#!/usr/bin/env python
#
# idle.py - Run functions on an idle loop or in a separate thread.
#
# Author: Paul McCarthy <pauldmccarthy@gmail.com>
#
"""This module provides functions and classes for running tasks
asynchronously, either in an idle loop, or on a separate thread.
.. note:: The *idle* functions in this module are intended to be run from
within a ``wx`` application. However, they will still work without
``wx``, albeit with slightly modified behaviour.
Idle tasks
----------
.. autosummary::
:nosignatures:
idle
idleWhen
inIdle
cancelIdle
idleReset
getIdleTimeout
setIdleTimeout
The :func:`idle` function is a simple way to run a task on an ``wx``
``EVT_IDLE`` event handler. This effectively performs the same job as the
:func:`run` function, but is more suitable for short tasks which do not
warrant running in a separate thread.
The ``EVT_IDLE`` event is generated automatically by ``wx``. However, there
are some circumstances in which ``EVT_IDLE`` will not be generated, and
pending events may be left on the queue. For this reason, the
:func:`_wxIdleLoop` will occasionally use a ``wx.Timer`` to ensure that it
continues to be called. The time-out used by this ``Timer`` can be queried
and set via the :func:`getIdleTimeout` and :func:`setIdleTimeout` functions.
Thread tasks
------------
.. autosummary::
:nosignatures:
run
wait
TaskThread
The :func:`run` function simply runs a task in a separate thread. This
doesn't seem like a worthy task to have a function of its own, but the
:func:`run` function additionally provides the ability to schedule another
function to run on the ``wx.MainLoop`` when the original function has
completed. This therefore gives us a simple way to run a computationally
intensitve task off the main GUI thread (preventing the GUI from locking up),
and to perform some clean up/refresh afterwards.
The :func:`wait` function is given one or more ``Thread`` instances, and a
task to run. It waits until all the threads have finished, and then runs
the task (via :func:`idle`).
The :class:`TaskThread` class is a simple thread which runs a queue of tasks.
Other facilities
----------------
The ``idle`` module also defines the :func:`mutex` decorator, which is
intended to be used to mark the methods of a class as being mutually exclusive.
The ``mutex`` decorator uses the :class:`MutexFactory` class to do its work.
"""
import time
import atexit
import logging
import functools
import threading
import collections
try: import queue
except ImportError: import Queue as queue
log = logging.getLogger(__name__)
def run(task, onFinish=None, onError=None, name=None):
"""Run the given ``task`` in a separate thread.
:arg task: The function to run. Must accept no arguments.
:arg onFinish: An optional function to schedule (on the ``wx.MainLoop``,
via :func:`idle`) once the ``task`` has finished.
:arg onError: An optional function to be called (on the ``wx.MainLoop``,
via :func:`idle`) if the ``task`` raises an error. Passed
the ``Exception`` that was raised.
:arg name: An optional name to use for this task in log statements.
:returns: A reference to the ``Thread`` that was created.
.. note:: If a ``wx`` application is not running, the ``task`` and
``onFinish`` functions will simply be called directly, and
the return value will be ``None``.
"""
from fsl.utils.platform import platform as fslplatform
if name is None:
name = getattr(task, '__name__', '<unknown>')
haveWX = fslplatform.haveGui
# Calls the onFinish or onError handler
def callback(cb, *args, **kwargs):
if cb is None:
return
if haveWX: idle(cb, *args, **kwargs)
else: cb( *args, **kwargs)
# Runs the task, and calls
# callback functions as needed.
def wrapper():
try:
task()
log.debug('Task "{}" finished'.format(name))
callback(onFinish)
except Exception as e:
log.warning('Task "{}" crashed'.format(name), exc_info=True)
callback(onError, e)
# If WX, run on a thread
if haveWX:
log.debug('Running task "{}" on thread'.format(name))
thread = threading.Thread(target=wrapper)
thread.start()
return thread
# Otherwise run directly
else:
log.debug('Running task "{}" directly'.format(name))
wrapper()
return None
_idleRegistered = False
"""Boolean flag indicating whether the :func:`_wxIdleLoop` function has
been registered as a ``wx.EVT_IDLE`` event handler. Checked and set
in the :func:`idle` function.
"""
_idleQueue = queue.Queue()
"""A ``Queue`` of functions which are to be run on the ``wx.EVT_IDLE``
loop.
"""
_idleQueueDict = {}
"""A ``dict`` containing the names of all named tasks which are
currently queued on the idle loop (see the ``name`` parameter to the
:func:`idle` function).
"""
_idleTimer = None
"""A ``wx.Timer`` instance which is used to periodically trigger the
:func:`_wxIdleLoop` in circumstances where ``wx.EVT_IDLE`` events may not
be generated. This is created in the first call to :func:`idle`.
"""
_idleCallRate = 200
"""Minimum time (in milliseconds) between consecutive calls to
:func:`_wxIdleLoop`. If ``wx.EVT_IDLE`` events are not being fired, the
:attr:`_idleTimer` is used to maintain the idle loop at this rate.
"""
def idleReset():
"""Reset the internal :func:`idle` queue state.
In a normal execution environment, this function will never need to be
called. However, in an execution environment where multiple ``wx.App``
instances are created, run, and destroyed sequentially, this function
will need to be called after each ``wx.App`` has been destroyed.
Otherwise the ``idle`` function will not work during exeution of
subsequent ``wx.App`` instances.
"""
global _idleRegistered
global _idleQueue
global _idleQueueDict
global _idleTimer
global _idleCallRate
if _idleTimer is not None:
_idleTimer.Stop()
# If we're atexit, the ref
# to the queue module might
# have been cleared.
if queue is not None: newQueue = queue.Queue()
else: newQueue = None
_idleRegistered = False
_idleQueue = newQueue
_idleQueueDict = {}
_idleTimer = None
_idleCallRate = 200
# Call idleReset on exit, in
# case the idleTimer is active.
atexit.register(idleReset)
def getIdleTimeout():
"""Returns the current ``wx`` idle loop time out/call rate.
"""
return _idleCallRate
def setIdleTimeout(timeout=None):
"""Set the ``wx`` idle loop time out/call rate. If ``timeout`` is not
provided, or is set to ``None``, the timeout is set to 200 milliseconds.
"""
global _idleCallRate
if timeout is None:
timeout = 200
log.debug('Idle loop timeout changed to {}'.format(timeout))
_idleCallRate = timeout
class IdleTask(object):
"""Container object used by the :func:`idle` and :func:`_wxIdleLoop`
functions.
"""
def __init__(self,
name,
task,
schedtime,
after,
timeout,
args,
kwargs):
self.name = name
self.task = task
self.schedtime = schedtime
self.after = after
self.timeout = timeout
self.args = args
self.kwargs = kwargs
def _wxIdleLoop(ev):
"""Function which is called on ``wx.EVT_IDLE`` events, and occasionally
on ``wx.EVT_TIMER` events via the :attr:`_idleTimer`. If there
is a function on the :attr:`_idleQueue`, it is popped and called.
.. note:: The ``wx.EVT_IDLE`` event is only triggered on user interaction
(e.g. mouse movement). This means that a situation may arise
whereby a function is queued via the :func:`idle` function, but
no ``EVT_IDLE`` event gets generated. Therefore, the
:attr:`_idleTimer` object is occasionally used to call this
function as well.
"""
import wx
global _idleQueue
global _idleQueueDict
global _idleTimer
global _idleCallRate
ev.Skip()
try:
task = _idleQueue.get_nowait()
except queue.Empty:
# Make sure that we get called periodically,
# if EVT_IDLE decides to stop firing. If
# _idleTimer is None, then idleReset has
# probably been called.
if _idleTimer is not None:
_idleTimer.Start(_idleCallRate, wx.TIMER_ONE_SHOT)
return
now = time.time()
elapsed = now - task.schedtime
queueSizeOffset = 0
taskName = task.name
funcName = getattr(task.task, '__name__', '<unknown>')
if taskName is None: taskName = funcName
else: taskName = '{} [{}]'.format(taskName, funcName)
# Has enough time elapsed
# since the task was scheduled?
# If not, re-queue the task.
# If this is the only task on the
# queue, the idle loop will be
# called again after
# _idleCallRate millisecs.
if elapsed < task.after:
log.debug('Re-queueing function ({}) on wx idle loop'.format(taskName))
_idleQueue.put_nowait(task)
queueSizeOffset = 1
# Has the task timed out?
elif task.timeout == 0 or (elapsed < task.timeout):
log.debug('Running function ({}) on wx idle loop'.format(taskName))
try:
task.task(*task.args, **task.kwargs)
except Exception as e:
log.warning('Idle task {} crashed - {}: {}'.format(
taskName, type(e).__name__, str(e)), exc_info=True)
if task.name is not None:
try: _idleQueueDict.pop(task.name)
except KeyError: pass
# More tasks on the queue?
# Request anotherd event
if _idleQueue.qsize() > queueSizeOffset:
ev.RequestMore()
# Otherwise use the idle
# timer to make sure that
# the loop keeps ticking
# over
else:
_idleTimer.Start(_idleCallRate, wx.TIMER_ONE_SHOT)
def inIdle(taskName):
"""Returns ``True`` if a task with the given name is queued on the
idle loop (or is currently running), ``False`` otherwise.
"""
global _idleQueueDict
return taskName in _idleQueueDict
def cancelIdle(taskName):
"""If a task with the given ``taskName`` is in the idle queue, it
is cancelled. If the task is already running, it cannot be cancelled.
A ``KeyError`` is raised if no task called ``taskName`` exists.
"""
global _idleQueueDict
_idleQueueDict[taskName].timeout = -1
def idle(task, *args, **kwargs):
"""Run the given task on a ``wx.EVT_IDLE`` event.
:arg task: The task to run.
:arg name: Optional. If provided, must be provided as a keyword
argument. Specifies a name that can be used to query
the state of this task via the :func:`inIdle` function.
:arg after: Optional. If provided, must be provided as a keyword
argument. A time, in seconds, which specifies the
amount of time to wait before running this task after
it has been scheduled.
:arg timeout: Optional. If provided, must be provided as a keyword
argument. Specifies a time out, in seconds. If this
amount of time passes before the function gets
scheduled to be called on the idle loop, the function
is not called, and is dropped from the queue.
:arg dropIfQueued: Optional. If provided, must be provided as a keyword
argument. If ``True``, and a task with the given
``name`` is already enqueud, that function is dropped
from the queue, and the new task is enqueued. Defaults
to ``False``. This argument takes precedence over the
``skipIfQueued`` argument.
:arg skipIfQueued: Optional. If provided, must be provided as a keyword
argument. If ``True``, and a task with the given
``name`` is already enqueud, (or is running), the
function is not called. Defaults to ``False``.
:arg alwaysQueue: Optional. If provided, must be provided as a keyword
argument. If ``True``, and a ``wx.MainLoop`` is not
running, the task is enqueued anyway, under the
assumption that a ``wx.MainLoop`` will be started in
the future. Note that, if ``wx.App`` has not yet been
created, another call to ``idle`` must be made after
the app has been created for the original task to be
executed. If ``wx`` is not available, this parameter
will be ignored, and the task executed directly.
All other arguments are passed through to the task function.
If a ``wx.App`` is not running, the ``timeout``, ``name`` and
``skipIfQueued`` arguments are ignored. Instead, the call will sleep for
``after`` seconds, and then the ``task`` is called directly.
.. note:: If the ``after`` argument is used, there is no guarantee that
the task will be executed in the order that it is scheduled.
This is because, if the required time has not elapsed when
the task is popped from the queue, it will be re-queued.
.. note:: If you schedule multiple tasks with the same ``name``, and you
do not use the ``skipIfQueued`` or ``dropIfQueued`` arguments,
all of those tasks will be executed, but you will only be able
to query/cancel the most recently enqueued task.
.. note:: You will run into difficulties if you schedule a function that
expects/accepts its own keyword arguments called ``name``,
``skipIfQueued``, ``dropIfQueued``, ``after``, ``timeout``, or
``alwaysQueue``.
"""
from fsl.utils.platform import platform as fslplatform
global _idleRegistered
global _idleTimer
global _idleQueue
global _idleQueueDict
schedtime = time.time()
timeout = kwargs.pop('timeout', 0)
after = kwargs.pop('after', 0)
name = kwargs.pop('name', None)
dropIfQueued = kwargs.pop('dropIfQueued', False)
skipIfQueued = kwargs.pop('skipIfQueued', False)
alwaysQueue = kwargs.pop('alwaysQueue', False)
canHaveGui = fslplatform.canHaveGui
haveGui = fslplatform.haveGui
# If there is no possibility of a
# gui being available in the future,
# then alwaysQueue is ignored.
if haveGui or (alwaysQueue and canHaveGui):
import wx
app = wx.GetApp()
# Register on the idle event
# if an app is available
#
# n.b. The 'app is not None' test will
# potentially fail in scenarios where
# multiple wx.Apps have been instantiated,
# as it may return a previously created
# app.
if (not _idleRegistered) and (app is not None):
log.debug('Registering async idle loop')
app.Bind(wx.EVT_IDLE, _wxIdleLoop)
_idleTimer = wx.Timer(app)
_idleRegistered = True
_idleTimer.Bind(wx.EVT_TIMER, _wxIdleLoop)
if name is not None and inIdle(name):
if dropIfQueued:
# The cancelIdle function sets the old
# task timeout to -1, so it won't get
# executed. But the task is left in the
# _idleQueue, and in the _idleQueueDict.
# In the latter, the old task gets
# overwritten with the new task below.
cancelIdle(name)
log.debug('Idle task ({}) is already queued - '
'dropping the old task'.format(name))
elif skipIfQueued:
log.debug('Idle task ({}) is already queued '
'- skipping it'.format(name))
return
log.debug('Scheduling idle task ({}) on wx idle '
'loop'.format(getattr(task, '__name__', '<unknown>')))
idleTask = IdleTask(name,
task,
schedtime,
after,
timeout,
args,
kwargs)
_idleQueue.put_nowait(idleTask)
if name is not None:
_idleQueueDict[name] = idleTask
else:
time.sleep(after)
log.debug('Running idle task directly')
task(*args, **kwargs)
def idleWhen(func, condition, *args, **kwargs):
"""Poll the ``condition`` function periodically, and schedule ``func`` on
:func:`idle` when it returns ``True``.
:arg func: Function to call.
:arg condition: Function which returns ``True`` or ``False``. The ``func``
function is only called when the ``condition`` function
returns ``True``.
:arg pollTime: Must be passed as a keyword argument. Time (in seconds) to
wait between successive calls to ``when``. Defaults to
``0.2``.
"""
pollTime = kwargs.get('pollTime', 0.2)
if not condition():
idle(idleWhen, func, condition, after=pollTime, *args, **dict(kwargs))
else:
kwargs.pop('pollTime', None)
idle(func, *args, **kwargs)
def wait(threads, task, *args, **kwargs):
"""Creates and starts a new ``Thread`` which waits for all of the ``Thread``
instances to finsih (by ``join``ing them), and then runs the given
``task`` via :func:`idle`.
If the ``direct`` parameter is ``True``, or a ``wx.App`` is not running,
this function ``join``s the threads directly instead of creating a new
``Thread`` to do so.
:arg threads: A ``Thread``, or a sequence of ``Thread`` instances to
join. Elements in the sequence may be ``None``.
:arg task: The task to run once all ``threads`` have completed.
:arg wait_direct: Must be passed as a keyword argument. If ``True``, this
function call will ``join`` all of the ``threads``, and
then call the ``task``. Otherwise (the default), this
function will create a new thread to ``join`` the
``threads``, and will return immediately.
All other arguments are passed to the ``task`` function.
.. note:: This function will not support ``task`` functions which expect
a keyword argument called ``wait_direct``.
"""
from fsl.utils.platform import platform as fslplatform
direct = kwargs.pop('wait_direct', False)
if not isinstance(threads, collections.Sequence):
threads = [threads]
haveWX = fslplatform.haveGui
def joinAll():
log.debug('Wait thread joining on all targets')
for t in threads:
if t is not None:
t.join()
log.debug('Wait thread scheduling task on idle loop')
idle(task, *args, **kwargs)
if haveWX and not direct:
thread = threading.Thread(target=joinAll)
thread.start()
return thread
else:
joinAll()
return None
class Task(object):
"""Container object which encapsulates a task that is run by a
:class:`TaskThread`.
"""
def __init__(self, name, func, onFinish, args, kwargs):
self.name = name
self.func = func
self.onFinish = onFinish
self.args = args
self.kwargs = kwargs
self.enabled = True
class TaskThreadVeto(Exception):
"""Task functions which are added to a :class:`TaskThread` may raise
a ``TaskThreadVeto`` error to skip processing of the task's ``onFinish``
handler (if one has been specified). See the :meth:`TaskThread.enqueue`
method for more details.
"""
pass
class TaskThread(threading.Thread):
"""The ``TaskThread`` is a simple thread which runs tasks. Tasks may be
enqueued and dequeued.
"""
def __init__(self, *args, **kwargs):
"""Create a ``TaskThread``. """
threading.Thread.__init__(self, *args, **kwargs)
self.__q = queue.Queue()
self.__enqueued = {}
self.__stop = False
log.debug('New task thread')
def enqueue(self, func, *args, **kwargs):
"""Enqueue a task to be executed.
:arg func: The task function.
:arg taskName: Task name. Must be specified as a keyword
argument. Does not necessarily have to be a string, but
must be hashable. If you wish to use the :meth:`dequeue`
or :meth:`isQueued` methods, you must provide a task
name.
:arg onFinish: An optional function to be called (via :func:`idle`)
when the task funtion has finished. Must be provided as
a keyword argument. If the ``func`` raises a
:class`TaskThreadVeto` error, this function will not
be called.
All other arguments are passed through to the task function when it is
executed.
.. note:: If the specified ``taskName`` is not unique (i.e. another
task with the same name may already be enqueued), the
:meth:`isQueued` method will probably return invalid
results.
.. warning:: Make sure that your task function is not expecting keyword
arguments called ``taskName`` or ``onFinish``!
"""
name = kwargs.pop('taskName', None)
onFinish = kwargs.pop('onFinish', None)
log.debug('Enqueueing task: {} [{}]'.format(
name, getattr(func, '__name__', '<unknown>')))
t = Task(name, func, onFinish, args, kwargs)
self.__enqueued[name] = t
self.__q.put(t)
def isQueued(self, name):
"""Returns ``True`` if a task with the given name is enqueued,
``False`` otherwise.
"""
return name in self.__enqueued
def dequeue(self, name):
"""Dequeues a previously enqueued task.
:arg name: The task to dequeue.
"""
task = self.__enqueued.get(name, None)
if task is not None:
log.debug('Dequeueing task: {}'.format(name))
task.enabled = False
def stop(self):
"""Stop the ``TaskThread`` after any currently running task has
completed.
"""
log.debug('Stopping task thread')
self.__stop = True
def waitUntilIdle(self):
"""Causes the calling thread to block until the task queue is empty.
"""
self.__q.join()
def run(self):
"""Run the ``TaskThread``. """
while True:
try:
# Clear ref to previous task if any. This
# is very important, because otherwise, if
# no tasks get posted to the queue, this
# loop will spin on queue.Empty exceptions,
# and the previous Task object will preserve
# a hanging ref to its function/method. Not
# ideal if the ref is to a method of the
# object which created this TaskThread, and
# needs to be GC'd!
task = None
# An example: Without clearing the task
# reference, the following code would
# result in the TaskThread spinning on empty
# forever, and would prevent the Blah
# instance from being GC'd:
#
# class Blah(object):
# def __init__(self):
# tt = TaskThraed()
# tt.enqueue(self.method)
# tt.start()
#
# def method(self):
# pass
#
# b = Blah()
# del b
task = self.__q.get(timeout=1)
except queue.Empty:
continue
# Any other error typically indicates
# that this is a daemon thread, and
# the TaskThread object has been GC'd
except Exception:
break
finally:
if self.__stop:
break
self.__enqueued.pop(task.name, None)
if not task.enabled:
self.__q.task_done()
continue
log.debug('Running task: {} [{}]'.format(
task.name,
getattr(task.func, '__name__', '<unknown>')))
try:
task.func(*task.args, **task.kwargs)
if task.onFinish is not None:
idle(task.onFinish)
log.debug('Task completed: {} [{}]'.format(
task.name,
getattr(task.func, '__name__', '<unknown>')))
# If the task raises a TaskThreadVeto error,
# we just have to skip the onFinish handler
except TaskThreadVeto:
log.debug('Task completed (vetoed onFinish): {} [{}]'.format(
task.name,
getattr(task.func, '__name__', '<unknown>')))
except Exception as e:
log.warning('Task crashed: {} [{}]: {}: {}'.format(
task.name,
getattr(task.func, '__name__', '<unknown>'),
type(e).__name__,
str(e)),
exc_info=True)
finally:
self.__q.task_done()
self.__q = None
self.__enqueued = None
log.debug('Task thread finished')
def mutex(*args, **kwargs):
"""Decorator for use on methods of a class, which makes the method
call mutually exclusive.
If you define a class which has one or more methods that must only
be accessed by one thread at a time, you can use the ``mutex`` decorator
to enforce this restriction. As a contrived example::
class Example(object):
def __init__(self):
self.__sharedData = []
@mutex
def dangerousMethod1(self, message):
sefl.__sharedData.append(message)
@mutex
def dangerousMethod2(self):
return sefl.__sharedData.pop()
The ``@mutex`` decorator will ensure that, at any point in time, only
one thread is running either of the ``dangerousMethod1`` or
``dangerousMethod2`` methods.
See the :class:`MutexFactory``
"""
return MutexFactory(*args, **kwargs)
class MutexFactory(object):
"""The ``MutexFactory`` is a placeholder for methods which have been
decorated with the :func:`mutex` decorator. When the method of a class
is decorated with ``@mutex``, a ``MutexFactory`` is created.
Later on, when the method is accessed on an instance, the :meth:`__get__`
method creates the true decorator function, and replaces the instance
method with that decorator.
.. note:: The ``MutexFactory`` adds an attribute called
``_async_mutex_lock`` to all instances that have
``@mutex``-decorated methods.
"""
createLock = threading.Lock()
"""This lock is used by all ``MutexFactory`` instances when a decorated
instance method is accessed for the first time.
The first time that a mutexed method is accessed on an instance, a new
``threading.Lock`` is created, to be shared by all mutexed methods of that
instance. The ``createLock`` is used to ensure that this can only occur
once for each instance.
"""
def __init__(self, function):
"""Create a ``MutexFactory``.
"""
self.__func = function
def __get__(self, instance, cls):
"""When this ``MutexFactory`` is accessed through an instance,
a decorator function is created which enforces mutually exclusive
access to the decorated method. A single ``threading.Lock`` object
is shared between all ``@mutex``-decorated methods on a single
instance.
If this ``MutexFactory`` is accessed through a class, the
decorated function is returned.
"""
# Class-level access
if instance is None:
return self.__func
# Get the lock object, creating if it necessary.
# We use the createLock in case multiple threads
# access a method at the same time, in which case
# only one of them will be able to create the
# instance lock.
with MutexFactory.createLock:
lock = getattr(instance, '_idle_mutex_lock', None)
if lock is None:
lock = threading.Lock()
instance._idle_mutex_lock = lock
# The true decorator function
def decorator(*args, **kwargs):
with instance._idle_mutex_lock:
return self.__func(instance, *args, **kwargs)
# Replace this MutexFactory with
# the decorator on the instance
decorator = functools.update_wrapper(decorator, self.__func)
setattr(instance, self.__func.__name__, decorator)
return decorator