I am reading myself into multighreading in python and came up with this simple test: (btw. this implementation might be very bad, I just wrote that down quickly for testing purpose. Buf if there is something terribly wrong I would be thankful if you could point that out)
#!/usr/bin/python2.7
import threading
import timeit
lst = range(0, 100000)
lstres = []
lstlock = threading.Lock()
lstreslock = threading.Lock()
def add_five(x):
return x+5
def worker_thread(args):
print "started"
while len(lst) > 0:
lstlock.acquire()
try:
x = lst.pop(0)
except IndexError:
lstlock.release()
return
lstlock.release()
x = add_five(x)
lstreslock.acquire()
lstres.append(x)
lstreslock.release()
def test():
try:
t1 = threading.Thread(target = worker_thread, args = (1,))
#t2 = threading.Thread(target = worker_thread, args = (2,))
#t3 = threading.Thread(target = worker_thread, args = (3,))
#t4 = threading.Thread(target = worker_thread, args = (4,))
t1.start();
#t2.start();
#t3.start();
#t4.start();
t1.join();
#t2.join();
#t3.join();
#t4.join();
except:
print "Error"
print len(lstres)
if __name__ == "__main__":
t = timeit.Timer(test)
print t.timeit(2)
Despite the terrible example I see the following: one thread is faster than 4. With one thread I get: 13.46 seconds, and with 4 threads: 25.47 seconds.
Is the access to the list by 4 threads a bottleneck thus causing slower times or did I do something wrong?
