[Python-Dev] GIL behaviour under Windows

[Sturla Molden]

Antoine Pitrou skrev:
> Kristján sent me a patch which I applied and is supposed to fix this.
> Anyway, thanks for the numbers. The GIL does seem to fare a bit better (zero
> latency with the Pi calculation in the background) than under Linux, although it
> may be caused by the limited resolution of time.time() under Windows.
>
>   

My critisism of the GIL on python-ideas was partly motivated by this:

http://blip.tv/file/2232410

However, David Beazley is not talking about Windows. Since the GIL is 
apparently not a mutex on Windows, it could behave differently. So I 
wrote a small script that contructs a GIL battle, and record how often a 
check-interval results in a thread-switch or not. For monitoring check 
intervals, I used a small C extension to read _Py_Ticker from ceval.c. 
It is not declared static so I could easily hack into it.

With two threads and a check interval og 100, only 61 of 100000 check 
intervals failed to produce a thread-switch in the interpreter. I'd call 
that rather fair. :-)

And in case someone asks, the nthreads=1 case is just for verification.

S.M.




D:\>test.py
check interval = 1
nthreads=1, swiched=0, missed=100000
nthreads=2, swiched=57809, missed=42191
nthreads=3, swiched=91535, missed=8465
nthreads=4, swiched=99751, missed=249
nthreads=5, swiched=95839, missed=4161
nthreads=6, swiched=100000, missed=0

D:\>test.py
check interval = 10
nthreads=1, swiched=0, missed=100000
nthreads=2, swiched=99858, missed=142
nthreads=3, swiched=99992, missed=8
nthreads=4, swiched=100000, missed=0
nthreads=5, swiched=100000, missed=0
nthreads=6, swiched=100000, missed=0

D:\>test.py
check interval = 100
nthreads=1, swiched=0, missed=100000
nthreads=2, swiched=99939, missed=61
nthreads=3, swiched=100000, missed=0
nthreads=4, swiched=100000, missed=0
nthreads=5, swiched=100000, missed=0
nthreads=6, swiched=100000, missed=0

D:\>test.py
check interval = 1000
nthreads=1, swiched=0, missed=100000
nthreads=2, swiched=99999, missed=1
nthreads=3, swiched=100000, missed=0
nthreads=4, swiched=100000, missed=0
nthreads=5, swiched=100000, missed=0
nthreads=6, swiched=100000, missed=0