# lock_ex.py
#
# A simple example of using a mutex lock for critical sections

import threading

x      = 0                   # A shared value
x_lock = threading.Lock()    # A lock for synchronizing access to x

COUNT = 1000000
def foo():
    global x
    for i in xrange(COUNT):
        x_lock.acquire()
        x += 1
        x_lock.release()

def bar():
    global x
    for i in xrange(COUNT):
        x_lock.acquire()
        x -= 1
        x_lock.release()

t1 = threading.Thread(target=foo)
t2 = threading.Thread(target=bar)
t1.start()
t2.start()
t1.join()
t2.join()
print x