Python Socket async send and receive design

Question

I am writing a python socket client which

Send out message one (e.g. Hello) every 5 seconds and message two (e.g. 15 seconds) every 15 seconds
Receive message at any time

I mean to do the send and receive in different thread. However it is still blocking. Does anyone has suggestion?

Thread #1

threading.Thread(target=Thread2, args=(sock)).start()
sock.recv(1024)

Thread #2

def Thread2(sock):
    count = 0
    while True:
        sleep(5)
        count = count + 5
        sock.send('Hello')
        if count % 15 == 0
            sock.send('15 seconds')

If you want an answer, please post the relevant part of the code that you have written. Or you'll risk to get the question closed — Francesco Montesano
– Francesco Montesano, Commented Mar 14, 2013 at 8:57

freakish · Accepted Answer · 2013-03-14 16:43:25Z

3

It is not blocking. It's just that your main thread does nothing after first sock.recv(1024). You have to tell it to constantly gather the data:

MAIN THREAD

threading.Thread(target=Thread2, args=(sock,)).start()
while True:
    data = sock.recv(1024)
    if not data:
        break
    print data

Note that you won't be able to interrupt that process easily. In order to do that you need to set thread as daemon:

MAIN THREAD

t = threading.Thread(target=Thread2, args=(sock,))
t.daemon = True
t.start()
while True:
    data = sock.recv(1024)
    if not data:
        break
    print data

Also when you are passing args remember to pass a tuple, i.e. args=(sock,) instead of args=(sock). For Python args=(sock) is equivalent to args=sock. This is probably the culprit!

I can't see more issues in your code.

edited Mar 14, 2013 at 16:43

answered Mar 14, 2013 at 16:38

freakish

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7 Comments

Winston Over a year ago

Thanks for your answer. I just know that the python offers a module called asyncore/asynchat. Can I use that to achieve non-blocking I/O?

freakish Over a year ago

@Winston Sorry for this late response (somehow I've missed the question). Yep, you can use it for non-blocking I/O (I've been using asyncore a bit in my work).

MrObjectOriented Over a year ago

Is this implementation thread-safe?

freakish Over a year ago

@ReeshabhRanjan no, it won't be. As long as there are only two threads, one only reading and one only writing there will be no issue.

MrObjectOriented Over a year ago

I see, thank you. Also nice to see people addressing comments on their answers after so many years. I wish you good luck in life. :)

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