Python0017 thread lock

Python0017 thread lock

Some problems with thread creation and threads have been introduced in the previous article. This article reproduces the problem mentioned in the previous article and uses thread locks to solve that problem.

After the thread is locked, other threads will wait for the lock to be released before continuing to execute when they encounter the lock.

Here is the code:

import threading
import time

sumab = -1


def a_thread():
    overall summation
    time.sleep(0.1)
    sumab = 0
    print("a:","sumab=0")
    time.sleep(0.1)
    sum = 1+2
    print("a:","sumab=1+2")
    time.sleep(0.1)
    print("a:","print sum")
    print("1+2=",sumab)

def b_thread():
    overall summation
    time.sleep(0.1)
    sumab = 1
    print("b:","sumab=1")
    time.sleep(0.1)
    sum = 3+4
    print("b:","sumab=3+4")
    time.sleep(0.1)
    print("b:","print sum")
    print("3+4=",sumab)
    
a=threading.Thread(target=a_thread)
b=threading.Thread(target=b_thread)
a.start()
b.start()

# A certain execution result
# a: sumb=0
# b: sumab=1
# a: sumb=1+2
# b: sumab=3+4
# a: print sum
# 1+2= 7
# b: print sum
# 3+4= 7


sumab_lock=threading.Lock()
def c_thread():
    global sumab,sumab_lock
    time.sleep(0.1)
    #lock
    sumab_lock.acquire()
    sumab = 0
    time.sleep(0.1)
    sum = 1+2
    time.sleep(0.1)
    print("1+2=",sumab)
    #release lock
    sumab_lock.release()

def d_thread():
    global sumab,sumab_lock
    time.sleep(0.1)
    
    #lock
    sumab_lock.acquire()
    sumab = 1
    time.sleep(0.1)
    sum = 3+4
    time.sleep(0.1)
    print("3+4=",sumab)
    #release lock
    sumab_lock.release()
    
c=threading.Thread(target=c_thread)
d=threading.Thread(target=d_thread)
c.start()
d.start()

# 1+2= 3
# 3+4= 7
#or
# 3+4= 7
# 1+2= 3