How to synchronize threads in python?

Question

I have two threads in python (2.7). I start them at the beginning of my program. While they execute, my program reaches the end and exits, killing both of my threads before waiting for resolution.

I'm trying to figure out how to wait for both threads to finish before exiting.

def connect_cam(ip, execute_lock):
    try:
        conn = TelnetConnection.TelnetClient(ip)
        execute_lock.acquire()
        ExecuteUpdate(conn, ip)
        execute_lock.release()
    except ValueError:
        pass


execute_lock = thread.allocate_lock()
thread.start_new_thread(connect_cam, ( headset_ip, execute_lock ) )
thread.start_new_thread(connect_cam, ( handcam_ip, execute_lock ) )

In .NET I would use something like WaitAll() but I haven't found the equivalent in python. In my scenario, TelnetClient is a long operation which may result in a failure after a timeout.

Answer 1

Thread is meant as a lower level primitive interface to Python's threading machinery - use threading instead. Then, you can use threading.join() to synchronize threads.

Other threads can call a thread’s join() method. This blocks the calling thread until the thread whose join() method is called is terminated.

Answer 2

Yoo can do something like that:

import threading

class connect_cam(threading.Thread):

    def __init__(self, ip, execute_lock):
        threading.Thread.__init__(self)
        self.ip = ip
        self.execute_lock = execute_lock

    def run(self):
        try:
            conn = TelnetConnection.TelnetClient(self.ip)
            self.execute_lock.acquire()
            ExecuteUpdate(conn, self.ip)
            self.execute_lock.release()
        except ValueError:
            pass


execute_lock = thread.allocate_lock()
tr1 = connect_cam(headset_ip, execute_lock)
tr2 = connect_cam(handcam_ip, execute_lock)
tr1.start()
tr2.start()
tr1.join()
tr2.join()

With the method .join(), the two threads (tr1 and tr2) will wait for each other.

Answer 3

First, you ought to be using the threading module, not the thread module. Next, have your main thread join() the other threads.