CODEWITHSUNDEEP
pythonmultithreading
Arrow
Arrow

Reputation: 711

Why does python thread still run while waiting?

I'm curious as to why the while loop in below code still runs after I told it to wait on a event object.

import threading, time
msg = threading.Event()

def sec():
    print  "second thread starting now.."
    counter = 0

    while True:
    #while msg.isSet():
        print "hello"
        print counter
        counter += 1
        time.sleep(3)
        msg.wait()

secThread = threading.Thread(target = sec)
secThread.start()

print "a"
msg.set()
time.sleep(5)
print "b"
msg.set()

And I get the following output

second thread starting now..a

hello
0
hello
1
b
hello
2
hello
3
....
(keeps going)

I can fix it with the commented out while loop, but I'm curious as to why it still ran. The main thread is done running so nothing should be setting the threading event to allow the second thread to run.

Thank you.

Upvotes: 0

Views: 184

Answers (1)

David Schwartz
David Schwartz

Reputation: 182769

Since msg is set (you set it), the loop does not need to wait. If you want to make the loop wait, call clear on the event. You can make the loop call msg.clear() after msg.wait returns if you wish.

Upvotes: 2

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