> From: Andreas Schwab <schwab@suse.de> > Date: Fri, 01 Feb 2002 11:49:22 +0100 > There is no way to find out anything about intermediate values of *p when > compare_and_swap returns zero. The value of *p can change anytime, even > if it only was different from oldval just at the time compare_and_swap did > the comparison. So there is zero chance that a spurious failure of > compare_and_swap breaks anything. Something to watch out for, though, is livelock. Consider the situation in which two processors are competing for a cache line, and both only win at the 'wrong' time: when computing a new value to be passed to compare_and_swap rather than when actually trying to perform the compare_and_swap. This is why on powerpc the loop is coded in the asm statement. -- - Geoffrey Keating <geoffk@geoffk.org> <geoffk@redhat.com>
