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, signal, socketserver

class WorkerServer(socketserver.UnixStreamServer):
    def __init__(self, server_address, RequestHandlerClass, socket):
        print('worker created: %s' % (os.getpid(), ))
        socketserver.BaseServer.__init__(self, server_address, RequestHandlerClass)
        self.socket = socket

class MasterServer(socketserver.UnixStreamServer):
    max_nchildren = 5

    def __init__(self, server_address, RequestHandlerClass, bind_and_activate=True):
        socketserver.UnixStreamServer.__init__(self, server_address, RequestHandlerClass, bind_and_activate)
        self.children = set()
        signal.signal(signal.SIGCHLD, self.reap_workers)

    def serve_forever(self, interval=0.5):
        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:
                worker = WorkerServer(self.server_address, self.RequestHandlerClass, self.socket)
                worker.serve_forever()
            except Exception as ex:
                print(ex)
            finally:
                sys.exit(0)
        else:
            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, *args):
        for pid in self.children.copy():
            try:
                pid, _ = os.waitpid(pid, os.WNOHANG)
                self.children.discard(pid)
            except ChildProcessError:
                self.children.discard(pid)
            except OSError:
                pass

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

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

server = MasterServer('/tmp/server', myhandler)
server.serve_forever()