CODEWITHSUNDEEP
pythonpipepython-multiprocessing
user1633361
user1633361

Reputation: 141

Multiprocessing using Pipes - application always stops after about 5 minutes

I'm developing a simple application to test Pipes in Python. The application starts a new process, that works as "server". The "server" starts another two worker processes, that send some data to the "server" When "server" receives a message, it is supposed to update its state, send it to all workers and also to the main process. But the application always stops after receiving 278 messages. What am I doing wrong? Here is the code:

class Server ( multiprocessing.Process ):

    def __init__( self, connection ):
        super( Server, self ).__init__()
        self.conn = connection

    def run( self ):
        state = []
        conn1a, conn1b = multiprocessing.Pipe()
        conn2a, conn2b = multiprocessing.Pipe()
        p1 = multiprocessing.Process( target=worker, args=(conn1b, 2, 'p1', 1 ) )
        p2 = multiprocessing.Process( target=worker, args=(conn2b, 3, 'p2', -1 ) )
        p1.start()
        p2.start()
        counter = 0
        while 1:
            if conn1a.poll() or conn2a.poll():
                if conn1a.poll():
                    state = conn1a.recv()
                if conn2a.poll():
                    state = conn2a.recv()
                self.conn.send( state )
                conn1a.send( state )
                conn2a.send( state )
                counter += 1
                print "counter", counter
        p1.join()
        p2.join()

def worker( conn, seconds, name, multiplier ):
    x = 0
    conn.send( [name, x*multiplier] )
    while 1:
        if conn.poll():
            x += seconds
            time.sleep( seconds )
            conn.send( [name, x*multiplier] )

if __name__ == '__main__':
    conn1, conn2 = multiprocessing.Pipe( False )
    p = Server( conn2 )
    p.start()
    while 1:
        print "received", conn1.recv()
    p.join()

Output of the application is as follows:

enter codstarting process p2
received ['p2', 0]
counter 1
starting process p1
received ['p1', 0]
counter 2
received ['p1', 2]
counter 3
...
counter 277
received ['p1', 332]
counter 278
received ['p2', -333]

Upvotes: 1

Views: 94

Answers (1)

baldr
baldr

Reputation: 2999

You forgot to read from the pipe in the workers. And the pipe gets filled.

    if conn.poll():
        conn.recv()  # consume messages!
        x += seconds

Upvotes: 1

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