Proper use of mutexes in Python
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()
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
I would like to improve answer from chris-b a little bit more.
See below for my code:
from threading import Thread, Lock
import threading
mutex = Lock()
def processData(data, thread_safe):
if thread_safe:
mutex.acquire()
try:
thread_id = threading.get_ident()
print('\nProcessing data:', data, "ThreadId:", thread_id)
finally:
if thread_safe:
mutex.release()
counter = 0
max_run = 100
thread_safe = False
while True:
some_data = counter
t = Thread(target=processData, args=(some_data, thread_safe))
t.start()
counter = counter + 1
if counter >= max_run:
break
In your first run if you set thread_safe = False
in while loop, mutex will not be used, and threads will step over each others in print method as below;
but, if you set thread_safe = True
and run it, you will see all the output comes perfectly fine;
hope this helps.
You have to unlock your Mutex at sometime...