62 lines
2.0 KiB
Python
62 lines
2.0 KiB
Python
from __future__ import print_function
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from eventlet import event as _event
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class metaphore(object):
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"""This is sort of an inverse semaphore: a counter that starts at 0 and
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waits only if nonzero. It's used to implement a "wait for all" scenario.
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>>> from eventlet import coros, spawn_n
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>>> count = coros.metaphore()
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>>> count.wait()
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>>> def decrementer(count, id):
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... print("{0} decrementing".format(id))
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... count.dec()
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...
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>>> _ = spawn_n(decrementer, count, 'A')
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>>> _ = spawn_n(decrementer, count, 'B')
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>>> count.inc(2)
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>>> count.wait()
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A decrementing
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B decrementing
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"""
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def __init__(self):
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self.counter = 0
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self.event = _event.Event()
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# send() right away, else we'd wait on the default 0 count!
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self.event.send()
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def inc(self, by=1):
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"""Increment our counter. If this transitions the counter from zero to
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nonzero, make any subsequent :meth:`wait` call wait.
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"""
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assert by > 0
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self.counter += by
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if self.counter == by:
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# If we just incremented self.counter by 'by', and the new count
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# equals 'by', then the old value of self.counter was 0.
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# Transitioning from 0 to a nonzero value means wait() must
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# actually wait.
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self.event.reset()
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def dec(self, by=1):
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"""Decrement our counter. If this transitions the counter from nonzero
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to zero, a current or subsequent wait() call need no longer wait.
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"""
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assert by > 0
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self.counter -= by
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if self.counter <= 0:
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# Don't leave self.counter < 0, that will screw things up in
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# future calls.
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self.counter = 0
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# Transitioning from nonzero to 0 means wait() need no longer wait.
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self.event.send()
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def wait(self):
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"""Suspend the caller only if our count is nonzero. In that case,
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resume the caller once the count decrements to zero again.
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"""
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self.event.wait()
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