Python threading. Why are the threads blocking on each other?

Question

import threading
import time

def someMethod(x):
    time.sleep(20)
    print(x);

def someMethod2(x):
    time.sleep(1)
    print(x);

t1 = threading.Thread(name="t1", target=someMethod(1));
t2 = threading.Thread(name="t2", target=someMethod2(2));

t1.start();
t2.start();

I'd expect the output to be 2 followed by 1 but it is 1 followed by 2. Total time is 21 seconds. How can I make it run in parallel so the output is 2 followed by 1 and both threads run in parallel so the total time is 20 units?

Apparently you called `someMethod` twice? Or was it for the sake of example? — LFB, Jun 19 '18 at 01:28

ShadowRanger · Accepted Answer · 2018-06-19T20:21:05.607

You called the functions in the main thread and passed their return values as the thread entry point (since they both returned None, this meant a no-op entry point), you didn't actually run them in separate threads. You also called someMethod twice, and never called someMethod2. To fix, change to:

t1 = threading.Thread(name="t1", target=someMethod, args=(1,))
t2 = threading.Thread(name="t2", target=someMethod2, args=(2,))

which properly passes references to the functions themselves as the entry points, with the arguments to be used, deferring execution until the thread is actually launched.

Python threading. Why are the threads blocking on each other?

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