Class JoinableQueue

Lib/multiprocessing/queues.py:314–351

#

class JoinableQueue(Queue):

    def __init__(self, maxsize=0, *, ctx):
        Queue.__init__(self, maxsize, ctx=ctx)
        self._unfinished_tasks = ctx.Semaphore(0)
        self._cond = ctx.Condition()

    def __getstate__(self):
        return Queue.__getstate__(self) + (self._cond, self._unfinished_tasks)

    def __setstate__(self, state):
        Queue.__setstate__(self, state[:-2])
        self._cond, self._unfinished_tasks = state[-2:]

    def put(self, obj, block=True, timeout=None):
        if self._closed:
            raise ValueError(f"Queue {self!r} is closed")
        if not self._sem.acquire(block, timeout):
            raise Full

        with self._notempty, self._cond:
            if self._thread is None:
                self._start_thread()
            self._buffer.append(obj)
            self._unfinished_tasks.release()
            self._notempty.notify()

    def task_done(self):
        with self._cond:
            if not self._unfinished_tasks.acquire(False):
                raise ValueError('task_done() called too many times')
            if self._unfinished_tasks._semlock._is_zero():
                self._cond.notify_all()

    def join(self):
        with self._cond:
            if not self._unfinished_tasks._semlock._is_zero():
                self._cond.wait()

#
# Simplified Queue type -- really just a locked pipe