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Re: Another multithreading bug (I think)
From: |
Wim Oudshoorn |
Subject: |
Re: Another multithreading bug (I think) |
Date: |
Mon, 11 Sep 2006 13:35:19 +0200 |
User-agent: |
Gnus/5.1002 (Gnus v5.10.2) Emacs/22.0.50 (darwin) |
Richard Frith-Macdonald <richard@tiptree.demon.co.uk> writes:
> - (id) sharedInstance
> {
> static volatile uint8_t isCreated = 0; // single byte
> declared volatile so we read from memory rather than a register
> static volatile id theInstance = nil;
>
> if (isCreated == 0)
> {
> [theLock lock];
> if (isCreated == 0 && theInstance == nil)
> {
> theInstance = [theClass new];
> }
> [theLock unlock];
> isCreated = 1;
> }
> return theInstance;
> }
I am not sure this is safe on a multiprocessor machine
Becauses I think that on a multiprocessor machine the following might happen:
Thread A on Processor A creates the instance and continues
Thread B on Processor B sees isCreated = 1, but still has a stale
value (nil) for 'theInstance' in its L1/L2 memory cache
and returns the nil.
- Re: Another multithreading bug (I think), (continued)
- Re: Another multithreading bug (I think), David Ayers, 2006/09/08
- Re: Another multithreading bug (I think), Richard Frith-Macdonald, 2006/09/08
- Multithreading, Wim Oudshoorn, 2006/09/08
- Re: Multithreading, Richard Frith-Macdonald, 2006/09/09
- Re: Multithreading, Wim Oudshoorn, 2006/09/09
- Re: Multithreading, Richard Frith-Macdonald, 2006/09/09
- Re: Another multithreading bug (I think),
Wim Oudshoorn <=
- Re: Another multithreading bug (I think), Pete French, 2006/09/11
- Re: Another multithreading bug (I think), Wim Oudshoorn, 2006/09/11
- Re: Another multithreading bug (I think), Wim Oudshoorn, 2006/09/11
- Re: Another multithreading bug (I think), Wim Oudshoorn, 2006/09/08