Thread Based Parallelism

Thread Based Parallelism - Thread Synchronization With Lock

    import threading

    shared_resource_with_lock = 0
    shared_resource_with_no_lock = 0
    COUNT = 100000
    shared_resource_lock = threading.Lock()


    ####LOCK MANAGEMENT##
    def increment_with_lock():
        global shared_resource_with_lock
        for i in range(COUNT):
            shared_resource_lock.acquire()
            shared_resource_with_lock += 1
            shared_resource_lock.release()


    def decrement_with_lock():
        global shared_resource_with_lock
        for i in range(COUNT):
            shared_resource_lock.acquire()
            shared_resource_with_lock -= 1
            shared_resource_lock.release()


    ####NO LOCK MANAGEMENT ##
    def increment_without_lock():
        global shared_resource_with_no_lock
        for i in range(COUNT):
            shared_resource_with_no_lock += 1


    def decrement_without_lock():
        global shared_resource_with_no_lock
        for i in range(COUNT):
            shared_resource_with_no_lock -= 1


    ####the Main program
    if __name__ == "__main__":
        t1 = threading.Thread(target=increment_with_lock)
        t2 = threading.Thread(target=decrement_with_lock)
        t3 = threading.Thread(target=increment_without_lock)
        t4 = threading.Thread(target=decrement_without_lock)
        t1.start()
        t2.start()
        t3.start()
        t4.start()
        t1.join()
        t2.join()
        t3.join()
        t4.join()
        print("the value of shared variable with lock management is %s" 
              % shared_resource_with_lock)
        print("the value of shared variable with race condition is %s" 
              % shared_resource_with_no_lock)

    Output,
        the value of shared variable with lock management is 0 
　　　　　　　　# 会发现 shared_resource_with_lock 恒定为 0;
　　　　　　　　# 因为 lock 的存在, increment 的数值等于 decrement 的数值.

　　　　 the value of shared variable with race condition is -9657
　　　　　　　　# shared_resource_with_no_lock 会为一个随机, 有时候也为 0.