Python 线程。如何锁定线程？

我试图理解线程和并发的基本知识。我想要一个简单的情况下，两个线程重复尝试访问一个共享资源。

密码:

import threading


class Thread(threading.Thread):
def __init__(self, t, *args):
threading.Thread.__init__(self, target=t, args=args)
self.start()
count = 0
lock = threading.Lock()


def increment():
global count
lock.acquire()
try:
count += 1
finally:
lock.release()
   

def bye():
while True:
increment()
        

def hello_there():
while True:
increment()


def main():
hello = Thread(hello_there)
goodbye = Thread(bye)
    

while True:
print count


if __name__ == '__main__':
main()

所以，我有两个线程，都试图增加计数器。我认为如果线程‘ A’称为 increment()，那么 lock就会建立起来，阻止‘ B’访问，直到‘ A’被释放。

运行 the 可以清楚地看到情况并非如此。您可以得到所有随机的数据增量。

锁对象到底是如何使用的？

另外，我尝试将锁放入线程函数中，但仍然没有结果。

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小开
最佳答案

You can see that your locks are pretty much working as you are using them, if you slow down the process and make them block a bit more. You had the right idea, where you surround critical pieces of code with the lock. Here is a small adjustment to your example to show you how each waits on the other to release the lock.

import threading
import time
import inspect


class Thread(threading.Thread):
def __init__(self, t, *args):
threading.Thread.__init__(self, target=t, args=args)
self.start()


count = 0
lock = threading.Lock()


def incre():
global count
caller = inspect.getouterframes(inspect.currentframe())[1][3]
print "Inside %s()" % caller
print "Acquiring lock"
with lock:
print "Lock Acquired"
count += 1
time.sleep(2)


def bye():
while count < 5:
incre()


def hello_there():
while count < 5:
incre()


def main():
hello = Thread(hello_there)
goodbye = Thread(bye)




if __name__ == '__main__':
main()

Sample output:

...
Inside hello_there()
Acquiring lock
Lock Acquired
Inside bye()
Acquiring lock
Lock Acquired
...
小开 
import threading


# global variable x
x = 0


def increment():
"""
function to increment global variable x
"""
global x
x += 1


def thread_task():
"""
task for thread
calls increment function 100000 times.
"""
for _ in range(100000):
increment()


def main_task():
global x
# setting global variable x as 0
x = 0


# creating threads
t1 = threading.Thread(target=thread_task)
t2 = threading.Thread(target=thread_task)


# start threads
t1.start()
t2.start()


# wait until threads finish their job
t1.join()
t2.join()


if __name__ == "__main__":
for i in range(10):
main_task()
print("Iteration {0}: x = {1}".format(i,x))

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