echo client and server programs shown previously
serve to illustrate socket fundamentals. But the server model suffers
from a fairly major flaw: if multiple clients try to connect to the
server, and it takes a long time to process a given clients’
request, the server will fail. More accurately, if the cost of
handling a given request prevents the server from returning to the
code that checks for new clients in a timely manner, it won’t
be able to keep up with all the requests, and some clients will
eventually be denied connections.
In real-world client/server programs, it’s far more typical to code a server so as to avoid blocking new requests while handling a current client’s request. Perhaps the easiest way to do so is to service each client’s request in parallel -- in a new process, in a new thread, or by manually switching (multiplexing) between clients in an event loop. This isn’t a socket issue per se, and we’ve already learned how to start processes and threads in Chapter 3. But since these schemes are so typical of socket server programming, let’s explore all three ways to handle client requests in parallel here.
The script in Example 10-4 works like the original
echo server, but instead forks a new process to
handle each new client connection. Because the
handleClient function runs in a new process, the
dispatcher function can immediately resume its
main loop, to detect and service a new incoming request.
Example 10-4. PP2E\Internet\Sockets\fork-server.py ...