Question

I want to run multiple threads simultaneously, and wait until all of them are done before continuing.

import subprocess

# I want these to happen simultaneously:
subprocess.call(scriptA + argumentsA)
subprocess.call(scriptA + argumentsB)
subprocess.call(scriptA + argumentsC)

# I want to wait until the above threads are all finished, and then run this:
print("All threads are done.")

---

I tried to use threading like the example here:

from threading import Thread
import subprocess

def call_script(args)
    subprocess.call(args)

t1 = Thread(target=call_script, args=(scriptA + argumentsA))
t2 = Thread(target=call_script, args=(scriptA + argumentsB))
t3 = Thread(target=call_script, args=(scriptA + argumentsC))

t1.start()
t2.start()
t3.start()

# TODO: Wait for all threads to finish.

print("All threads are done.")

How do I wait for the threads to finish before running the last line?

Answer 1

You need to use join method of Thread object in the end of the script.

t1 = Thread(target=call_script, args=(scriptA + argumentsA))
t2 = Thread(target=call_script, args=(scriptA + argumentsB))
t3 = Thread(target=call_script, args=(scriptA + argumentsC))

t1.start()
t2.start()
t3.start()

t1.join()
t2.join()
t3.join()

Thus the main thread will wait till t1, t2 and t3 finish execution.