Author: Dave Gomboc
Date: 22:59:55 11/05/02
Go up one level in this thread
On November 05, 2002 at 11:26:45, Robert Hyatt wrote: >On November 05, 2002 at 02:43:38, Gerd Isenberg wrote: > >>On November 05, 2002 at 02:01:51, Gian-Carlo Pascutto wrote: >> >>>On November 04, 2002 at 16:35:29, Gerd Isenberg wrote: >>> >>>><snip> >>>> >>>>Gian-Carlo, >>>> >>>>Isn't it necessary to use the lock prefix before xchg? >>> >>>I don't know Gerd. I based this snipped on the locking code >>>in Crafty, and it appears to work fine. >>> >>>-- >>>GCP >> >>Aha, then Bob Hyatt may answer this question. The lock prefix makes the >>"xchg"-instruction (read- and write cycle) atomic. So there may be rare cases, >>where two or more processers do the instruction at the same time, both reading >>the semaphore just before the write cycle occurs - and both get zero.... >>I thought the lock prefix is exactly for that purpose. >> >>Gerd > > >Good question. I will do some research. The spinlock code in crafty came >_directly_ >from the linux kernel spinlock. > >OK... From my Intel manual, vol 3 (operating systems): > >The LOCK prefix is automatically assumed for XCHG instruction... (page 7-4) > >So it seems that the current lock is correct... Does that mean your code is GPL now? ;-) Dave
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