Python線程。 如何鎖定線程？

Question

我試圖了解線程和並發的基礎知識。 我想要一個簡單的案例，其中兩個線程反復嘗試訪問一個共享資源。

代碼：

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

def bye():
    while True:
        incre()

def hello_there():
    while True:
        incre()

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

    while True:
        print count

if __name__ == '__main__':
    main()

所以，我有兩個線程，都試圖增加計數器。 我認為如果線程 'A' 調用了incre() ，則會建立lock ，阻止 'B' 訪問，直到 'A' 釋放。

運行 清楚地表明情況並非如此。 您將獲得所有隨機數據競爭性增量。

鎖對象究竟是如何使用的？

編輯，此外，我嘗試將鎖放在線程函數中，但仍然沒有運氣。

Answer 1

你可以看到你的鎖在你使用它們時非常有效，如果你減慢這個過程並讓它們阻塞更多一點。 你的想法是正確的，你用鎖包圍了關鍵的代碼片段。 這是對您的示例的一個小調整，以向您展示每個人如何等待另一個人釋放鎖定。

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()

示例輸出：

...
Inside hello_there()
Acquiring lock
Lock Acquired
Inside bye()
Acquiring lock
Lock Acquired
...

Answer 2

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))