#Python's condition variable

A condition variable is a synchronization mechanism used in operating systems and concurrent programming to coordinate communication between threads or processes. It allows a thread to wait when a certain condition is not met and be notified when another thread signals that the condition might have changed.

In Python, you can create a condition variable using the Condition class from the threading module. Use the wait method to wait for a signal, and the notify method to send a notification.

A condition variable includes an internal lock. You can pass a lock as an argument when creating a Condition; if omitted, it will automatically create a reentrant lock. You can acquire and release the lock using the acquire and release methods, or more commonly, use a with statement.

Here’s an example where a consumer thread waits until the variable count reaches 10 before proceeding:

from threading import Thread, Condition

count: int = 0
cond = Condition()

def consumer():
    global count

    while True:
        with cond:                  # Lock to protect count
            print('consumer')

            cond.wait()             # Atomically release the lock and wait for notification;
                                    # re-acquires the lock upon being notified
            if count == 10:         # Check the value of count
                print(count)
                break


def producer():
    global count

    while True:
        with cond:                  # Lock to protect count
            print('producer')
            count += 1              # Increment count
            cond.notify()           # Send notification

            if count == 10:         # Terminate when done
                break

t1 = Thread(target=consumer)        # Create thread
t2 = Thread(target=producer) 
t1.start()                          # Start thread
t2.start()
t1.join()                           # Wait for thread to finish
t2.join()