Coverage for src/lib/python/isc/util/socketserver_mixin : 86%

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import threading 

import socket 

import select 

SOCK_DATA = b'somedata' 

class NoPollMixIn: 

    '''This is a mix-in class to override the function serve_forever() 

    and shutdown() in class socketserver.BaseServer. 

    As commented in the module source code,  serve_forever() in 

    socketserver.BaseServer uses polling for a shutdown request, which 

    "reduces the responsiveness to a shutdown request and wastes cpu at 

    all other times." 

    This class fixes this problem by introducing internal message 

    passing via a separate socket. Note, however, that according to 

    the module documentation serve_forever() and shutdown() are not 

    categorized as functions that can be overridden via mix-ins.  So 

    this mix-in class may not be compatible with future versions of 

    socketserver.  It should be considered a short term workaround 

    until the original implementation is fixed. 

    The NoPollMixIn class should be used together with 

    socketserver.BaseServer or some derived classes of it, and it must 

    be placed before the corresponding socketserver class.  In 

    addition, the constructor of this mix-in must be called 

    explicitely in the derived class.  For example, a basic TCP server 

    without the problem of polling is created as follows: 

       class MyServer(NoPollMixIn, socketserver.TCPServer): 

           def __init__(...): 

               ... 

               NoPollMixIn.__init__(self) 

               ... 

    To shutdown the server correctly, the serve_forever() method must 

    be run in a separate thread, and shutdown() must be called from 

    some other thread. 

    ''' 

    def __init__(self): 

        self.__read_sock, self.__write_sock = socket.socketpair() 

        self._is_shut_down = threading.Event() 

    def serve_forever(self, poll_interval=None): 

        ''' Overrides the serve_forever([poll_interval]) in class 

        socketserver.BaseServer. 

        It uses a socketpair to wake up the select when shutdown() is 

        called in anther thread.  Note, parameter 'poll_interval' is 

        just used for interface compatibility; it's never used in this 

        function. 

        ''' 

        while True: 

            # block until the self.socket or self.__read_sock is readable 

            try: 

                r, w, e = select.select([self, self.__read_sock], [], []) 

            except select.error as err: 

                if err.args[0] == EINTR: 

                    continue 

                else: 

                    break 

            if self.__read_sock in r: 

                break 

            else: 

                self._handle_request_noblock(); 

        self._is_shut_down.set() 

    def shutdown(self): 

        '''Stops the serve_forever loop. 

        Blocks until the loop has finished, the function should be called 

        in another thread when serve_forever is running, or it will block. 

        ''' 

        self.__write_sock.send(SOCK_DATA) # make self.__read_sock readable. 

        self._is_shut_down.wait()  # wait until the serve thread terminate