CODEWITHSUNDEEP
pythonmultithreading
Matt Warren
Matt Warren

Reputation: 686

correct way to update attributes on one thread from another

I can best explain this with example code first;

class reciever(threading.Thread,simple_server):
    def __init__(self,callback):
        threading.Thread.__init__(self)
        self.callback=callback

    def run(self):
        self.serve_forever(self.callback)

class sender(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
        self.parameter=50

    def run(self):
        while True:
            #do some processing in general
            #....
            #send some udp messages derived from self.parameter
            send_message(self.parameter)

if __name__=='__main__':
    osc_send=sender()
    osc_send.start()

    def update_parameter(val):
        osc_send.parameter=val

    osc_recv=reciever(update_parameter)
    osc_recv.start()

the pieces I have left out are hopefully self explanatory from the code thats there..

My question is, is this a safe way to use a server running in a thread to update the attributes on a separate thread that could be reading the value at any time?

Upvotes: 0

Views: 941

Answers (1)

dano
dano

Reputation: 94881

The way you're updating that parameter is actually thread-safe already, because of the Global Interpreter Lock (GIL). The GIL means that Python only allows one thread to execute byte-code at a time, so it is impossible for one thread to be reading from parameter at the same time another thread is writing to it. Reading from and setting an attribute are both single, atomic byte-code operations; one will always start and complete before the other can happen. You would only need to introduce synchronization primitives if you needed to do operations that are more than one byte-code operation from more than one threads (e.g. incrementing parameter from multiple threads).

Upvotes: 3

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