Example of Threading in Python from https://www.tutorialspoint.com/python/python_multithreading.htm

threads_explanation.py

#!/usr/bin/python

import Queue
import threading
import time

exitFlag = 0

class myThread (threading.Thread):
    
    def __init__(self, threadID, name, q):
        threading.Thread.__init__(self)
        self.threadID = threadID
        self.name = name
        self.q = q
    
    def run(self):
        print "Starting " + self.name
        process_data(self.name, self.q)
        print "Exiting " + self.name

def process_data(threadName, q):
    # fr this method basically keeps checking the workqueue and processes anything in there
    # if there's nothing, it sleeps for 1 sec.
    
    while not exitFlag:
        queueLock.acquire() # fr Notice it's the same object initiated below - weird var scope much?
            if not workQueue.empty(): # fr again a var declared outside of this method
                data = q.get() # fr Can the queue handle the locking bit? It's supposed to be able to
                queueLock.release() # fr So now other Threads can do their things
                print("%s processing %s" % (threadName, data))
            else:
                print("%s sleeping, nothing in queue" % (threadName, data))
                queueLock.release()
            
            time.sleep(1)
            
            

threadList = ["Thread-1", "Thread-2", "Thread-3"]
nameList = ["One", "Two", "Three", "Four", "Five"]

# fr Gonna pass this Lock object around the place
queueLock = threading.Lock()

workQueue = Queue.Queue(10)
threads = []
threadID = 1

# Create new threads
for tName in threadList: # fr also notice that threads are starting but sitting there doing nothing as the queue is empty
    thread = myThread(threadID, tName, workQueue)
    thread.start()
    threads.append(thread)
    threadID += 1

# Fill the queue
queueLock.acquire() # fr now we acquire a lock to fill the queue, but did we need it? OR... 
# are we locking so we can fill it up completely and THEN process it... aaaah!
for word in nameList:
    workQueue.put(word)

queueLock.release()

# Wait for queue to empty
while not workQueue.empty(): # fr as we're still processing the main thread this of course is run
# Cant imagine it will take long though, but could move the timer around so it takes longer.
    pass

# Notify threads it's time to exit
# fr now set flag, thread can be at any stage of execution so will eventually hit that
# section with the 'while not exitFlag'
exitFlag = 1

# Wait for all threads to complete
# fr surely some of the threads have already completed?
for t in threads:
    t.join()
    
print "Exiting Main Thread"

can you please briefly explain what does exitFlag() variable does in this code?