process.py 文件源码

def __init__(self, max_workers=None):
        """Initializes a new ProcessPoolExecutor instance.

        Args:
            max_workers: The maximum number of processes that can be used to
                execute the given calls. If None or not given then as many
                worker processes will be created as the machine has processors.
        """
        _check_system_limits()

        if max_workers is None:
            self._max_workers = os.cpu_count() or 1
        else:
            self._max_workers = max_workers

        # Make the call queue slightly larger than the number of processes to
        # prevent the worker processes from idling. But don't make it too big
        # because futures in the call queue cannot be cancelled.
        self._call_queue = multiprocessing.Queue(self._max_workers +
                                                 EXTRA_QUEUED_CALLS)
        # Killed worker processes can produce spurious "broken pipe"
        # tracebacks in the queue's own worker thread. But we detect killed
        # processes anyway, so silence the tracebacks.
        self._call_queue._ignore_epipe = True
        self._result_queue = SimpleQueue()
        self._work_ids = queue.Queue()
        self._queue_management_thread = None
        # Map of pids to processes
        self._processes = {}

        # Shutdown is a two-step process.
        self._shutdown_thread = False
        self._shutdown_lock = threading.Lock()
        self._broken = False
        self._queue_count = 0
        self._pending_work_items = {}