Class _PoolCache

Lib/multiprocessing/pool.py:150–171

Class that implements a cache for the Pool class that will notify the pool management threads every time the cache is emptied. The notification is done by the use of a queue that is provided when instantiating the cache.

#

class _PoolCache(dict):
    """
    Class that implements a cache for the Pool class that will notify
    the pool management threads every time the cache is emptied. The
    notification is done by the use of a queue that is provided when
    instantiating the cache.
    """
    def __init__(self, /, *args, notifier=None, **kwds):
        self.notifier = notifier
        super().__init__(*args, **kwds)

    def __delitem__(self, item):
        super().__delitem__(item)

        # Notify that the cache is empty. This is important because the
        # pool keeps maintaining workers until the cache gets drained. This
        # eliminates a race condition in which a task is finished after the
        # the pool's _handle_workers method has enter another iteration of the
        # loop. In this situation, the only event that can wake up the pool
        # is the cache to be emptied (no more tasks available).
        if not self:
            self.notifier.put(None)

class Pool(object):
    '''