[EMAIL PROTECTED] wrote:
Ian Appru wrote:
While atomic increment/decrements (using cas) are suffiently well documented
for me to be pretty
confident in my implementation I would apreciate any input for an atomic
conditional increment.
I'd expect the following to work on OpenSolaris:
#include <atomic.h>
int atomic_conditional_increment(int *target)
{
for (;;) {
int old = *target;
if (old == 0)
return 0;
if (atomic_cas_uint((uint_t *) target, old, old + 1) == old)
return old + 1;
}
}
You will certainly need a membar before reading *target.
(If not, it can happen that one thread continuously sees "0" while
another CPU runs away incrementing the counter.
(And you function has a bug in that it will not always update a non-zero
target)
Casper
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Since SPARC is total store order (module vis) , and x86 is strongly
ordered (modulo SSE non-temporal writes and write-combining), the
membars aren't needed. The compiler shouldn't need target to be
declared volatile, either; passing the pointer to atomic_cas_uint
should force re-evaluation of *target inside the loop.
- Bart
--
Bart Smaalders Solaris Kernel Performance
[EMAIL PROTECTED] http://blogs.sun.com/barts
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