How to lock a thread in Python

Question

I am new to Python. I am learning the threading concept in Python. I want to know how to lock a thread when two threads are trying to access a shared resource

Answer 1

Please refer to the following code to solve the problem.

from threading import Lock, Thread
lock = Lock()
g = 0

def add_one():
   """
   Just used for demonstration. It's bad to use the 'global'
   statement in general.
   """
   
   global g
   lock.acquire()
   g += 1
   lock.release()

def add_two():
   global g
   lock.acquire()
   g += 2
   lock.release()

threads = []
for func in [add_one, add_two]:
   threads.append(Thread(target=func))
   threads[-1].start()

for thread in threads:
   """
   Waits for threads to complete before moving on with the main
   script.
   """
   thread.join()

print(g)

The output of this program will be 3

Answer 2

1. Lock objects can release the lock at any position of code. For example if test1 function calls the lock so this lock can be opened by another function. But in RLock thread must release it once for each time it has acquired it.
    

2. In recursive call of function Lock will produce the deadlock that can be overcome by Rlock.