Python Lock acquire()用法及代碼示例

Python Lock.acquire() 方法

acquire() 是 Python 中線程模塊的 Lock 類的內置方法。

此方法用於獲取鎖，阻塞或非阻塞。當它在沒有參數的情況下被調用時，它會阻塞調用線程，直到當前使用它的線程解鎖鎖。

模塊：

    from threading import Lock 

用法:

    acquire( blocking=True, timeout=-1)

參數：

• blocking:它是一個可選參數，用作阻塞標誌。如果設置為 True，調用線程將在其他線程持有該標誌時被阻塞，一旦該鎖被釋放，調用線程將獲取該鎖並返回 True。如果設置為 False，則如果其他線程已獲取鎖，則不會阻塞該線程，並返回 False。其默認值為 True。
• timeout:它是一個可選參數，它指定如果其他方法當前正在獲取鎖，調用線程將被阻塞的秒數。它的默認值是 -1，表示線程將被無限期阻塞，直到它獲得鎖。

注意:blocking 為 false 時禁止指定超時。

返回值：

這個方法的返回類型是<class 'bool'>.該函數用於在實現多線程時獲取鎖，如果成功獲取鎖則返回 True，否則返回 False。

例：

# Python program to show
# the use of acquire() method in Lock class
import threading
import random
                    
class shared(object):
  
    def __init__(self, x = 0):
        # Created a Lock object
        self.lock = threading.Lock()
        self.incr = x
        
        # Increment function for the thread
    def incrementcounter(self):
        print("Waiting for the lock to be unlocked")
        # Lock acquired by the current thread
        self.lock.acquire()
        try:
            print('Lock acquired, current counter value:', self.incr)
            self.incr = self.incr + 1
        finally:
            print('Lock released, current counter value:', self.incr)
            # Lock released by the given thread
            self.lock.release()

def helper_thread(c):
    # Getting a random integer between 1 to 3
    r = random.randint(1,3)
    print("Random value selected:", r)
    for i in range(r):
      c.incrementcounter()
    print('Finished', str(threading.current_thread().getName()))
    print()

if __name__ == '__main__':
    obj = shared()

    thread1 = threading.Thread(target=helper_thread, args=(obj,))
    thread1.start()
    
    thread2 = threading.Thread(target=helper_thread, args=(obj,))
    thread2.start()

    thread1.join()
    thread2.join()
    
    print('Final counter value:', obj.incr)

輸出

Random value selected:1
Waiting for the lock to be unlocked
Lock acquired, current counter value: 0
Lock released, current counter value: 1
Finished Thread-1

Random value selected:2
Waiting for the lock to be unlocked
Lock acquired, current counter value: 1
Lock released, current counter value: 2
Waiting for the lock to be unlocked
Lock acquired, current counter value: 2
Lock released, current counter value: 3
Finished Thread-2

Final counter value:3