prefork-echo-server.py

#! /usr/bin/env python3

# quick & dirty preforked echo server listening on /tmp/server
# client: socat unix-connect:/tmp/server stdout

import os, sys, time, socketserver

class PreforkMixIn:
    max_nchildren = 3
    children = None

    def spawn_workers_forever(self, interval=0.5):
        if self.children is None:
            self.children = set()
        while self.running():
            self.create_workers()
            self.reap_workers()
            time.sleep(interval)

    def running(self):
        return not os.path.exists('/tmp/exit')

    def create_worker(self):
        pid = os.fork()
        assert pid >= 0
        if pid == 0:
            try:
                self.serve_forever()
            except Exception as ex:
                print(ex)
            finally:
                sys.exit(0)
        else:
            print('added worker: %s' % pid)
            self.children.add(pid)

    def create_workers(self, interval=0.5):
        while len(self.children) < self.max_nchildren:
            self.create_worker()
            time.sleep(interval)

    def reap_workers(self):
        for pid in self.children.copy():
            try:
                pid, _ = os.waitpid(pid, os.WNOHANG)
                if pid:
                    print('removed worker: %s' % pid)
                self.children.discard(pid)
            except ChildProcessError:
                self.children.discard(pid)
            except OSError:
                pass

class myhandler(socketserver.StreamRequestHandler):
    def handle(self):
        print('serving from pid %s' % os.getpid())
        while 1:
            data = self.rfile.read(1)
            if not data:
                break
            self.wfile.write(data)

class myserver(PreforkMixIn, socketserver.UnixStreamServer):
    pass

if os.path.exists('/tmp/server'):
    os.unlink('/tmp/server')

server = myserver('/tmp/server', myhandler)
server.spawn_workers_forever()