import threading ,time
"""
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。
在这里 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
"""
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