Function main

Lib/multiprocessing/forkserver.py:293–440

Run forkserver.

(listener_fd, alive_r, preload, main_path=None, sys_path=None,
         *, sys_argv=None, authkey_r=None, on_error='ignore')

def main(listener_fd, alive_r, preload, main_path=None, sys_path=None,
         *, sys_argv=None, authkey_r=None, on_error='ignore'):
    """Run forkserver."""
    if authkey_r is not None:
        try:
            authkey = os.read(authkey_r, _AUTHKEY_LEN)
            assert len(authkey) == _AUTHKEY_LEN, f'{len(authkey)} < {_AUTHKEY_LEN}'
        finally:
            os.close(authkey_r)
    else:
        authkey = b''

    _handle_preload(preload, main_path, sys_path, sys_argv, on_error)

    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()]
                    if rfds:
                        break

                if alive_r in rfds:
                    # EOF because no more client processes left
                    assert os.read(alive_r, 1) == b'', "Not at EOF?"
                    raise SystemExit