Python Lock Class | release() Method with Example

Python Lock.release() Method: Here, we are going to learn about the release() method of Lock Class in Python with its definition, syntax, and examples.
Submitted by Hritika Rajput, on May 18, 2020

Python Lock.release() Method

release() is an inbuilt method of the Lock class of the threading module in Python.

This method releases the lock which was earlier acquired by a thread. Once the lock is released, only then can it be acquired by another thread. This can be called from any thread, not just from the thread that acquired it. When an unlocked lock is released, a RuntimeError is raised.

Module:

    from threading import Lock

Syntax:

    release()

Parameter(s):

  • None

Return value:

The return type of this method is <class 'NoneType'>. It releases the thread which had acquired it.

Example:

# Python program to show
# the use of release() 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)

Output

Random value selected: 2
Waiting for the lock to be unlocked
Lock acquired, current counter value:  0
Lock released, current counter value:  1
Waiting for the lock to be unlocked
Lock acquired, current counter value:  1
Lock released, current counter value:  2
Finished Thread-1

Random value selected: 3
Waiting for the lock to be unlocked
Lock acquired, current counter value:  2
Lock released, current counter value:  3
Waiting for the lock to be unlocked
Lock acquired, current counter value:  3
Lock released, current counter value:  4
Waiting for the lock to be unlocked
Lock acquired, current counter value:  4
Lock released, current counter value:  5
Finished Thread-2

Final counter value: 5






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