RLock Example

gistfile1.txt

import threading
import time 

class X:
    def __init__(self):
        self.a = 1
        self.b = 2
        self.lock = threading.RLock()

    def changeA(self):
        print(f"{threading.current_thread().name} waiting in changeA")
        with self.lock:
            print(f"{threading.current_thread().name} starting processing in changeA")
            time.sleep(5)
            self.a = self.a + 1

    def changeB(self):
        print(f"{threading.current_thread().name} waiting in changeB")
        with self.lock:
            print(f"{threading.current_thread().name} starting processing in changeB")
            self.b = self.b + self.a # this is an issue, as a can change while using it, should add a lock to access a

    def changeAandB(self):
        print(f"{threading.current_thread().name} waiting in changeAandB")
        with self.lock:
            print(f"{threading.current_thread().name} starting processing in changeAandB")
            self.changeA() # using rlock allows us the self.lock to be called again
            self.changeB()

if __name__ == "__main__":
    x = X()
    t1 = threading.Thread(target=x.changeA)
    t1.start()
    x.changeA() # like a normal lock, we can't do anything until we get it
    t1.join()

    print("---")

    t2 = threading.Thread(target=x.changeAandB)
    t2.start()
    x.changeB() # this can't happen until t2 is finished
    t2.join()