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"""Version of sched.scheduler with a fixed cancel() method."""
import heapq
import sched
class Scheduler(sched.scheduler):
"""A thread-safe, general purpose event scheduler."""
def cancel(self, event):
"""Remove an event from the queue.
Raises a ValueError if the event is not in the queue.
"""
# The changes from https://hg.python.org/cpython/rev/d8802b055474 made it so sched.Event
# instances returned by sched.scheduler.enter() and sched.scheduler.enterabs() are treated
# as equal if they have the same (time, priority). It is therefore possible to remove the
# wrong event from the list when sched.scheduler.cancel() is called. Note that this is still
# true even with time.monotonic being the default timefunc, as GetTickCount64() on Windows
# only has a resolution of ~15ms. We therefore use the `is` operator to remove the correct
# event from the list.
with self._lock:
for i in range(len(self._queue)):
if self._queue[i] is event:
del self._queue[i]
heapq.heapify(self._queue)
return
raise ValueError("event not in list")
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