GIL in alternative implementations

[Marc Christiansen]

Daniel Kluev <dan.kluev at gmail.com> wrote:
> test.py:
> 
> from threading import Thread
> class X(object):
>    pass
> obj = X()
> obj.x = 0
> 
> def f(*args):
>   for i in range(10000):
>       obj.x += 1
> 
> threads = []
> for i in range(100):
>    t = Thread(target=f)
>    threads.append(t)
>    t.start()
> 
> for t in threads:
>    while t.isAlive():
>        t.join(1)
> 
> print(obj.x)
> 
>> python test.py
> 1000000
>> pypy test.py
> 1000000
>> jython-2.5 test.py
> 19217
>> ipy test.py
> 59040
> 
> Not that this thing is reasonable to do in real code, but cpython and
> other implementations with GIL at least give you some safety margin.
> 
Sure? ;)
 > for p in python2.4 python2.5 python2.6 python2.7 python3.1 python3.2; do echo $p; $p /tmp/test.py; $p /tmp/test.py; done
 python2.4
 525369
 736202
 python2.5
 449496
 551023
 python2.6
 903405
 937335
 python2.7
 885834
 910144
 python3.1
 866557
 766842
 python3.2
 1000000
 1000000

So even CPython (at least < 3.2) isn't safe. And I wouldn't rely on 3.2
not to break.

Marc