I am really sorry for the OT :-( I asked elsewhere but without any
answer :-(
I can not figure out why in this short example the user+sys time is
bigger than real time. The example executes the task() functions twice,
with each execution in a separate thread. The task() just increment
10**6 times a global int:
$ cat foo.py
from threading import Thread, Lock
result = 0
lock = Lock()
def task():
global result
for i in range(10**6):
lock.acquire()
result += 1
lock.release()
if __name__ == '__main__':
t1, t2 = Thread(target=task), Thread(target=task)
t1.start()
t2.start()
t1.join()
t2.join()
print('result:', result)
When I execute it (Python 3.6), I get a sys+user time bigger than the
real time:
$ time python foo.py
result: 2000000
real 0m7.088s
user 0m6.597s
sys 0m5.043s
That is usually what I can expect in case of tasks executed in parallel
on different CPUs. But my example should not be the case, due to the
GIL. What am I missing? Thank you very much, and sorry again for the OT :(
--
Marco Buttu
INAF-Osservatorio Astronomico di Cagliari
Via della Scienza n. 5, 09047 Selargius (CA)
Phone: 070 711 80 217
Email: mbu...@oa-cagliari.inaf.it
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