python避免死锁方法实例分析

本文实例讲述了python避免死锁方法。分享给大家供大家参考。具体分析如下：

当两个或者更多的线程在等待资源的时候就会产生死锁，两个线程相互等待。
在本文实例中 thread1 等待thread2释放block , thread2等待thtead1释放ablock，

避免死锁的原则：

1. 一定要以一个固定的顺序来取得锁，这个列子中，意味着首先要取得alock, 然后再去block

2. 一定要按照与取得锁相反的顺序释放锁，这里，应该先释放block,然后是alock

    import threading ,time
    a = 5
    alock = threading.Lock()
    b = 5
    block = threading.Lock()
    def thread1calc():
      print "thread1 acquiring lock a"
      alock.acquire()
      time.sleep(5)
      print "thread1 acquiring lock b"
      block.acquire()
      a+=5
      b+=5
      print "thread1 releasing both locks"
      block.release()
      alock.release()
    def thread2calc():
      print "thread2 acquiring lock b"
      block.acquire()
      time.sleep(5)
      print "thread2 acquiring lock a"
      alock.acquire()
      time.sleep(5)
      a+=10
      b+=10
      print "thread2 releasing both locks"
      block.release()
      alock.release()
    t = threading.Thread(target = thread1calc)
    t.setDaemon(1)
    t.start()
    t = threading.Thread(target = thread2calc)
    t.setDaemon(2)
    t.start()
    while 1:
      time.sleep(300)

输出：

    thread1 acquiring lock a
    thread2 acquiring lock b
    thread1 acquiring lock b
    thread2 acquiring lock a

希望本文所述对大家的Python程序设计有所帮助。