Sometimes, two scripts need to communicate some information between themselves via two processes. In Unix/Linux, there's a concept of connected socket, of socketpair. We can experiment with this here.
This recipe is designed for a Unix/Linux host. Windows/Mac is not suitable for running this one.
We use a test_socketpair() function to wrap a few lines that test the socket's socketpair() function.
List 3.8 shows an example of socketpair, as follows:
#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter – 3
# This program is optimized for Python 2.7.
# It may run on any other version with/without modifications.
import socket
import os
BUFSIZE = 1024
def test_socketpair():
""" Test Unix socketpair"""
parent, child = socket.socketpair()
pid = os.fork()
try:
if pid:
print "@Parent, sending message..."
child.close()
parent.sendall("Hello from parent!")
response = parent.recv(BUFSIZE)
print "Response from child:", response
parent.close()
else:
print "@Child, waiting for message from parent"
parent.close()
message = child.recv(BUFSIZE)
print "Message from parent:", message
child.sendall("Hello from child!!")
child.close()
except Exception, err:
print "Error: %s" %err
if __name__ == '__main__':
test_socketpair()The output from the preceding script is as follows:
$ python 3_8_ipc_using_socketpairs.py @Parent, sending message... @Child, waiting for message from parent Message from parent: Hello from parent! Response from child: Hello from child!!
The socket.socketpair() function simply returns two connected socket objects. In our case, we can say that one is a parent and another is a child. We fork another process via a os.fork() call. This returns the process ID of the parent. In each process, the other process' socket is closed first and then a message is exchanged via a sendall() method call on the process's socket. The try-except block prints any error in case of any kind of exception.