1 Thread Based Parallelism - Thread Synchronization With Lock
2
3 import threading
4
5 shared_resource_with_lock = 0
6 shared_resource_with_no_lock = 0
7 COUNT = 100000
8 shared_resource_lock = threading.Lock()
9
10
11 ####LOCK MANAGEMENT##
12 def increment_with_lock():
13 global shared_resource_with_lock
14 for i in range(COUNT):
15 shared_resource_lock.acquire()
16 shared_resource_with_lock += 1
17 shared_resource_lock.release()
18
19
20 def decrement_with_lock():
21 global shared_resource_with_lock
22 for i in range(COUNT):
23 shared_resource_lock.acquire()
24 shared_resource_with_lock -= 1
25 shared_resource_lock.release()
26
27
28 ####NO LOCK MANAGEMENT ##
29 def increment_without_lock():
30 global shared_resource_with_no_lock
31 for i in range(COUNT):
32 shared_resource_with_no_lock += 1
33
34
35 def decrement_without_lock():
36 global shared_resource_with_no_lock
37 for i in range(COUNT):
38 shared_resource_with_no_lock -= 1
39
40
41 ####the Main program
42 if __name__ == "__main__":
43 t1 = threading.Thread(target=increment_with_lock)
44 t2 = threading.Thread(target=decrement_with_lock)
45 t3 = threading.Thread(target=increment_without_lock)
46 t4 = threading.Thread(target=decrement_without_lock)
47 t1.start()
48 t2.start()
49 t3.start()
50 t4.start()
51 t1.join()
52 t2.join()
53 t3.join()
54 t4.join()
55 print("the value of shared variable with lock management is %s" \
56 % shared_resource_with_lock)
57 print("the value of shared variable with race condition is %s" \
58 % shared_resource_with_no_lock)
59
60 Output,
61 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.
62 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.
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