python创建进程fork用法

#!coding=utf-8
import os ,traceback
import time
'''
fork()系统调用是Unix下以自身进程创建子进程的系统调用，
一次调用，两次返回，如果返回是0，
则是子进程，如果返回值>0，则是父进程（返回值是子进程的pid）
'''
source = 10
i = 0
try:
  print '***********************'
  pid = os.fork()
  #这里会返回两次，所以下面的省略号会输出2次
  print '......'
  if pid == 0:#子进程
    print "this is child process"
    source = source - 1
    print 'child process source is ',source
    time.sleep(10)
    print 'child sleep done'
  else:  #父进程
    print "this is parent process"
    print 'parent process source is ',source
    time.sleep(10)
    print 'parent sleep done'
  print source
except:
  traceback.print_exc()

***********************
......
this is child process
child process source is 9
......
this is parent process
parent process source is 10
child sleep done
9
parent sleep done
10