1+ import time
2+ import multiprocessing
3+ 4+ def deposit (balance ):
5+ for i in range (100 ):
6+ time .sleep (0.01 )
7+ balance .value = balance .value + 1
8+ 9+ 10+ def withdraw (balance ):
11+ for i in range (100 ):
12+ time .sleep (0.01 )
13+ balance .value = balance .value - 1
14+ 15+ def problem ():
16+ balance = multiprocessing .Value ('i' , 200 )
17+ d = multiprocessing .Process (target = deposit , args = (balance , ))
18+ w = multiprocessing .Process (target = withdraw , args = (balance , ))
19+ 20+ d .start ()
21+ w .start ()
22+ 23+ d .join ()
24+ w .join ()
25+ # it should print 200 but it does not
26+ print ("After transactions: " , balance .value )
27+ 28+ 29+ def deposit_solution (balance , lock ):
30+ for i in range (100 ):
31+ time .sleep (0.01 )
32+ lock .acquire ()
33+ balance .value = balance .value + 1
34+ lock .release ()
35+ 36+ 37+ def withdraw_solution (balance , lock ):
38+ for i in range (100 ):
39+ time .sleep (0.01 )
40+ lock .acquire ()
41+ balance .value = balance .value - 1
42+ lock .release ()
43+ 44+ 45+ def solution ():
46+ balance = multiprocessing .Value ('i' , 200 )
47+ lock = multiprocessing .Lock ()
48+ d = multiprocessing .Process (target = deposit_solution , args = (balance , lock ))
49+ w = multiprocessing .Process (target = withdraw_solution , args = (balance , lock ))
50+ 51+ d .start ()
52+ w .start ()
53+ 54+ d .join ()
55+ w .join ()
56+ # it should print 200 but it does not
57+ print ("After transactions: " , balance .value )
58+ 59+ if __name__ == '__main__' :
60+ problem ()
61+ solution ()
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