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| """A generally useful event scheduler class. | |
| Each instance of this class manages its own queue. | |
| No multi-threading is implied; you are supposed to hack that | |
| yourself, or use a single instance per application. | |
| Each instance is parametrized with two functions, one that is | |
| supposed to return the current time, one that is supposed to | |
| implement a delay. You can implement real-time scheduling by | |
| substituting time and sleep from built-in module time, or you can | |
| implement simulated time by writing your own functions. This can | |
| also be used to integrate scheduling with STDWIN events; the delay | |
| function is allowed to modify the queue. Time can be expressed as | |
| integers or floating point numbers, as long as it is consistent. | |
| Events are specified by tuples (time, priority, action, argument, kwargs). | |
| As in UNIX, lower priority numbers mean higher priority; in this | |
| way the queue can be maintained as a priority queue. Execution of the | |
| event means calling the action function, passing it the argument | |
| sequence in "argument" (remember that in Python, multiple function | |
| arguments are be packed in a sequence) and keyword parameters in "kwargs". | |
| The action function may be an instance method so it | |
| has another way to reference private data (besides global variables). | |
| """ | |
| import time | |
| import heapq | |
| from collections import namedtuple | |
| from itertools import count | |
| import threading | |
| from time import monotonic as _time | |
| __all__ = ["scheduler"] | |
| Event = namedtuple('Event', 'time, priority, sequence, action, argument, kwargs') | |
| Event.time.__doc__ = ('''Numeric type compatible with the return value of the | |
| timefunc function passed to the constructor.''') | |
| Event.priority.__doc__ = ('''Events scheduled for the same time will be executed | |
| in the order of their priority.''') | |
| Event.sequence.__doc__ = ('''A continually increasing sequence number that | |
| separates events if time and priority are equal.''') | |
| Event.action.__doc__ = ('''Executing the event means executing | |
| action(*argument, **kwargs)''') | |
| Event.argument.__doc__ = ('''argument is a sequence holding the positional | |
| arguments for the action.''') | |
| Event.kwargs.__doc__ = ('''kwargs is a dictionary holding the keyword | |
| arguments for the action.''') | |
| _sentinel = object() | |
| class scheduler: | |
| def __init__(self, timefunc=_time, delayfunc=time.sleep): | |
| """Initialize a new instance, passing the time and delay | |
| functions""" | |
| self._queue = [] | |
| self._lock = threading.RLock() | |
| self.timefunc = timefunc | |
| self.delayfunc = delayfunc | |
| self._sequence_generator = count() | |
| def enterabs(self, time, priority, action, argument=(), kwargs=_sentinel): | |
| """Enter a new event in the queue at an absolute time. | |
| Returns an ID for the event which can be used to remove it, | |
| if necessary. | |
| """ | |
| if kwargs is _sentinel: | |
| kwargs = {} | |
| with self._lock: | |
| event = Event(time, priority, next(self._sequence_generator), | |
| action, argument, kwargs) | |
| heapq.heappush(self._queue, event) | |
| return event # The ID | |
| def enter(self, delay, priority, action, argument=(), kwargs=_sentinel): | |
| """A variant that specifies the time as a relative time. | |
| This is actually the more commonly used interface. | |
| """ | |
| time = self.timefunc() + delay | |
| return self.enterabs(time, priority, action, argument, kwargs) | |
| def cancel(self, event): | |
| """Remove an event from the queue. | |
| This must be presented the ID as returned by enter(). | |
| If the event is not in the queue, this raises ValueError. | |
| """ | |
| with self._lock: | |
| self._queue.remove(event) | |
| heapq.heapify(self._queue) | |
| def empty(self): | |
| """Check whether the queue is empty.""" | |
| with self._lock: | |
| return not self._queue | |
| def run(self, blocking=True): | |
| """Execute events until the queue is empty. | |
| If blocking is False executes the scheduled events due to | |
| expire soonest (if any) and then return the deadline of the | |
| next scheduled call in the scheduler. | |
| When there is a positive delay until the first event, the | |
| delay function is called and the event is left in the queue; | |
| otherwise, the event is removed from the queue and executed | |
| (its action function is called, passing it the argument). If | |
| the delay function returns prematurely, it is simply | |
| restarted. | |
| It is legal for both the delay function and the action | |
| function to modify the queue or to raise an exception; | |
| exceptions are not caught but the scheduler's state remains | |
| well-defined so run() may be called again. | |
| A questionable hack is added to allow other threads to run: | |
| just after an event is executed, a delay of 0 is executed, to | |
| avoid monopolizing the CPU when other threads are also | |
| runnable. | |
| """ | |
| # localize variable access to minimize overhead | |
| # and to improve thread safety | |
| lock = self._lock | |
| q = self._queue | |
| delayfunc = self.delayfunc | |
| timefunc = self.timefunc | |
| pop = heapq.heappop | |
| while True: | |
| with lock: | |
| if not q: | |
| break | |
| (time, priority, sequence, action, | |
| argument, kwargs) = q[0] | |
| now = timefunc() | |
| if time > now: | |
| delay = True | |
| else: | |
| delay = False | |
| pop(q) | |
| if delay: | |
| if not blocking: | |
| return time - now | |
| delayfunc(time - now) | |
| else: | |
| action(*argument, **kwargs) | |
| delayfunc(0) # Let other threads run | |
| @property | |
| def queue(self): | |
| """An ordered list of upcoming events. | |
| Events are named tuples with fields for: | |
| time, priority, action, arguments, kwargs | |
| """ | |
| # Use heapq to sort the queue rather than using 'sorted(self._queue)'. | |
| # With heapq, two events scheduled at the same time will show in | |
| # the actual order they would be retrieved. | |
| with self._lock: | |
| events = self._queue[:] | |
| return list(map(heapq.heappop, [events]*len(events))) |