Proper use of mutexes in Python

Question

I am starting with multi-threads in python (or at least it is possible that my script creates multiple threads). would this algorithm be the right usage of a Mutex? I haven't tested this code yet and it probably won't even work. I just want processData to run in a thread (one at time) and the main while loop to keep running, even if there is a thread in queue.

from threading import Thread from win32event import CreateMutex mutex = CreateMutex(None, False, "My Crazy Mutex") while(1)     t = Thread(target=self.processData, args=(some_data,))     t.start()     mutex.lock()  def processData(self, data)     while(1)         if mutex.test() == False:             do some stuff             break 

Edit: re-reading my code I can see that it is grossly wrong. but hey, that's why I am here asking for help.

Answer 1

I don't know why you're using the Window's Mutex instead of Python's. Using the Python methods, this is pretty simple:

from threading import Thread, Lock  mutex = Lock()  def processData(data):     mutex.acquire()     try:         print('Do some stuff')     finally:         mutex.release()  while True:     t = Thread(target = processData, args = (some_data,))     t.start() 

But note, because of the architecture of CPython (namely the Global Interpreter Lock) you'll effectively only have one thread running at a time anyway--this is fine if a number of them are I/O bound, although you'll want to release the lock as much as possible so the I/O bound thread doesn't block other threads from running.

An alternative, for Python 2.6 and later, is to use Python's multiprocessing package. It mirrors the threading package, but will create entirely new processes which can run simultaneously. It's trivial to update your example:

from multiprocessing import Process, Lock  mutex = Lock()  def processData(data):     with mutex:         print('Do some stuff')  if __name__ == '__main__':     while True:         p = Process(target = processData, args = (some_data,))         p.start() 

Answer 2

This is the solution I came up with:

import time from threading import Thread from threading import Lock  def myfunc(i, mutex):     mutex.acquire(1)     time.sleep(1)     print "Thread: %d" %i     mutex.release()   mutex = Lock() for i in range(0,10):     t = Thread(target=myfunc, args=(i,mutex))     t.start()     print "main loop %d" %i 

Output:

main loop 0 main loop 1 main loop 2 main loop 3 main loop 4 main loop 5 main loop 6 main loop 7 main loop 8 main loop 9 Thread: 0 Thread: 1 Thread: 2 Thread: 3 Thread: 4 Thread: 5 Thread: 6 Thread: 7 Thread: 8 Thread: 9