#!/usr/bin/python

 from multiprocessing import Process,Lock

 import time,sys

 def A(lock):

     with lock:

         for i in range(10):

             time.sleep(2)

             sys.stdout.write("hello world\n")

 def B(lock):

     lock.acquire()

     try:

         for i in range(10):

             time.sleep(2)

             sys.stdout.write("  nihao  a \n")

     finally:

         lock.release()

 lock=Lock()

 m=Process(target=A,args=(lock,))

 n=Process(target=B,args=(lock,))

 m.start()

 n.start()

 m.join()

 n.join()