Python Socket (Simple server script)

Question

I have this simple server script. My objective for this script is :

Wait for a client connection
Receive massages from client until the client disconnect
Once client disconnect, wait for another client to connect
Receive massages until the client disconnect
Repeat...

import socket

server_socket = socket.socket(socket.AF_INET,socket.SOCK_STREAM)
server_socket.bind(("",5000))
server_socket.listen(5)
print "Awaiting Client connection"
client_socket, address =server_socket.accept()
print "Connection established.. with ",address
while True:
    data=client_socket.recv(512)
    if not data:
        client_socket.close()
        print "Client disconnected, Awaiting new connections..."
        client_socket, address =server_socket.accept()
        print "Connection from ",address
    else:
        print "RECIEVED:",data

My Question is even though the script seems to be working when i test it on a pair of pc, i noticed that after it received the connection from the client, that is line no 7

print "Connection established.. with ",address

the python shell window seems unresponsive (become not responding if i try to move the shell window) until the client send any message.

As far as i understand, if there is no incoming message from client, client_socket.recv(512) will just wait for the data from the client.

But why it became unresponsive? To make things clearer,

-the script works just fine ( it receive data and print it out from screen & wait for the new connection if client disconnect)

-the cursor in console windows stop blinking

-when i try to move the console window around , it become unresponsive and windows give me a message "this program has stopped responding"

The recv method is blocking - see stackoverflow.com/questions/9770567/…. — planestepper
– planestepper, Commented Aug 30, 2013 at 3:36

Community · Accepted Answer · 2017-05-23 10:25:17Z

1

Basically, you script blocks on the accept call that is present after this line :

print "Client disconnected, Awaiting new connections..."

The accept call will return only when a particular client has attempted to connect to server. That is when your script will continue execution to the next line. This is the reason why you would see a message like This program is not responding in Windows.

You could consider the use of non-blocking socket I/O approach in order to ensure that your script is responsive.

Refer to this link for description of blocking and non-blocking calls. Also you can refer to this question to understand how to implement Non-blocking sockets in Python - and of course there are plenty of web resources too.

Hope this helps

edited May 23, 2017 at 10:25

CommunityBot

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answered Aug 30, 2013 at 4:29

Prahalad Deshpande

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