Function main

Lib/multiprocessing/forkserver.py:169–307

Run forkserver.

(listener_fd, alive_r, preload, main_path=None, sys_path=None)

#

def main(listener_fd, alive_r, preload, main_path=None, sys_path=None):
    '''Run forkserver.'''
    if preload:
        if sys_path is not None:
            sys.path[:] = sys_path
        if '__main__' in preload and main_path is not None:
            process.current_process()._inheriting = True
            try:
                spawn.import_main_path(main_path)
            finally:
                del process.current_process()._inheriting
        for modname in preload:
            try:
                __import__(modname)
            except ImportError:
                pass

        # gh-135335: flush stdout/stderr in case any of the preloaded modules
        # wrote to them, otherwise children might inherit buffered data
        util._flush_std_streams()

    util._close_stdin()

    sig_r, sig_w = os.pipe()
    os.set_blocking(sig_r, False)
    os.set_blocking(sig_w, False)

    def sigchld_handler(*_unused):
        # Dummy signal handler, doesn't do anything
        pass

    handlers = {
        # unblocking SIGCHLD allows the wakeup fd to notify our event loop
        signal.SIGCHLD: sigchld_handler,
        # protect the process from ^C
        signal.SIGINT: signal.SIG_IGN,
        }
    old_handlers = {sig: signal.signal(sig, val)
                    for (sig, val) in handlers.items()}

    # calling os.write() in the Python signal handler is racy
    signal.set_wakeup_fd(sig_w)

    # map child pids to client fds
    pid_to_fd = {}

    with socket.socket(socket.AF_UNIX, fileno=listener_fd) as listener, \
         selectors.DefaultSelector() as selector:
        _forkserver._forkserver_address = listener.getsockname()

        selector.register(listener, selectors.EVENT_READ)
        selector.register(alive_r, selectors.EVENT_READ)
        selector.register(sig_r, selectors.EVENT_READ)

        while True:
            try:
                while True:
                    rfds = [key.fileobj for (key, events) in selector.select()]