Thread Based Parallelism - Thread Synchronization With Lock

 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.