Reduce the number of active threads created by ThreadPoolExecutor?

Question

For a ThreadPoolExecutor, I want to monitor the number of threads which are actually running. But it seems that this is impossible. The number of active threads is continually increasing. For normal thread, if the target function returns, the thread will shutdown.

import threading, concurrent.futures

def test():
    pass

p_ac=threading.active_count()
#Number of threads=2

#for threads
trs=[None]*10
for i in range(10):
    trs[i]=threading.Thread(target=test)
    trs[i].start

print(threading.active_count()==p_ac)
#True

#for executor
executor=concurrent.futures.ThreadPoolExecutor(10)
for _ in range(10):
    executor.submit(test)
print(threading.active_count())
#Number of threads=12

Answer 1

The ThreadPoolExecutor does not shutdown its threads when active. ThreadPoolExecutor(X) creates X threads and keeps them alive until you shutdown the executor via executor.shutdown() or the executor itself decides it doesn't need so many threads. Anyway X is the expected amount of threads if the executor is active.