selectors2.py 文件源码

def DefaultSelector():
    """ This function serves as a first call for DefaultSelector to
    detect if the select module is being monkey-patched incorrectly
    by eventlet, greenlet, and preserve proper behavior. """
    global _DEFAULT_SELECTOR
    if _DEFAULT_SELECTOR is None:
        if platform.python_implementation() == 'Jython':  # Platform-specific: Jython
            _DEFAULT_SELECTOR = JythonSelectSelector
        elif _can_allocate('kqueue'):
            _DEFAULT_SELECTOR = KqueueSelector
        elif _can_allocate('devpoll'):
            _DEFAULT_SELECTOR = DevpollSelector
        elif _can_allocate('epoll'):
            _DEFAULT_SELECTOR = EpollSelector
        elif _can_allocate('poll'):
            _DEFAULT_SELECTOR = PollSelector
        elif hasattr(select, 'select'):
            _DEFAULT_SELECTOR = SelectSelector
        else:  # Platform-specific: AppEngine
            raise RuntimeError('Platform does not have a selector.')
    return _DEFAULT_SELECTOR()