python实现守护进程的方法

#!/usr/bin/python2.7
#coding=utf-8

import socket
import os
import sys
import Constants
from io import BytesIO as StringIO


def socket_server():
    f = StringIO()
    server_address = Constants.SOCKET_FILE

    # Make sure the socket does not already exist
    try:
        os.unlink(server_address)
    except OSError:
        if os.path.exists(server_address):
            raise

    # Create a UDS socket
    sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)

    # Bind the socket to the address
    print('starting up on {}'.format(server_address))
    sock.bind(server_address)

    # Listen for incoming connections
    sock.listen(1)

    while True:
        # Wait for a connection
        print('waiting for a connection')
        connection, client_address = sock.accept()
        try:
            print('connection from', client_address)

            # Receive the data in small chunks and retransmit it
            while True:
                data = connection.recv(16)
                print('received {!r}'.format(data))
                if data:
                    print('sending data back to the client')
                    if data == "get":
                        connection.sendall(read_from_memory(f))
                    else:
                        write_into_memory(f,data)
                else:
                    print('no data from', client_address)
                    break

        finally:
            # Clean up the connection
            connection.close()


def write_into_memory(string_io,info):
    """
    状态的写入分别包含：
    nodeId int      // 1 | 2
    redisState int  // 0: unknown, 1: master, 2: slave, [3, ]: down
    remoteOpState int // 0: unknown, 1: active
    masterId int    // 1 | 2, master node ID
    :return:
    """
    string_io.write(info)
    return


def read_from_memory(string_io):
    return string_io.read()




if __name__ == "__main__":
    # do the UNIX double-fork magic, see Stevens' "Advanced
    # Programming in the UNIX Environment" for details (ISBN 0201563177)
    try:
        pid = os.fork()
        if pid > 0:
            # exit first parent
            sys.exit(0)
    except OSError, e:
        print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
        sys.exit(1)
    # decouple from parent environment
    os.chdir("/")
    os.setsid()
    os.umask(0)
    # do second fork
    try:
        pid = os.fork()
        if pid > 0:
            # exit from second parent, print eventual PID before
            print "Daemon PID %d" % pid
            sys.exit(0)
    except OSError, e:
        print >>sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, e.strerror)
        sys.exit(1)
    # start the daemon main loop
    socket_server()