why the following python program does not face any concurrency problems without synchronize mechanism?

Alexander Kapps alex.kapps at web.de
Sat Jul 9 23:17:29 CEST 2011


On 09.07.2011 22:45, smith jack wrote:
> from threading import Thread
>
> def calc(start, end):
>      total = 0;
>      for i in range(start, end + 1):
>          total += i;
>      print '----------------------result:', total
>      return total
>
> t = Thread(target=calc, args=(1,100))
> t.start()
>
> I have run this program for many times,and the result is always 5050,
> if there is any concurrency problem, the result should not be 5050,
> which is never met, anyhow
> I mean this program should get the wrong answer at some times, but
> this never happens, why?
> can concurrency without synchronize mechanism always get the right answer?
> any special case in python programming?

Why do you think, that there's a concurrency problem?

All variables are local to the calc() function and all calc() 
invocations run in an own thread. No thread tries to access any 
shared data, so why should there be a concurrency problem?

Concurrency is an issue, when two or more threads/processes try to 
access the same data, but in your program everything is local to the 
calc() function.



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