Atomic increment and get?
mdf at FreeBSD.org
mdf at FreeBSD.org
Mon Oct 3 14:47:57 UTC 2011
2011/10/3 Lev Serebryakov <lev at freebsd.org>:
> Is here atomic increment and get (or add and get) operation in
> kernel? I cannot find one. Here is atomic_add_32(), but it doesn't
> return result. And here is no atomic_add_64() on 32 bit system :(
See atomic_fetchadd_int.
Not all hardware has 64-bit atomic instructions available in 32-bit
mode so it's not machine-independent. Generally, for this case (and
potentially for sub-32-bit atomic operations [1]) a lock is used.
[1] with masking and shifting 32-bit atomics can be used to set data
in an 8 or 16 bit variable; see a recent commit to sys/vm.
Cheers,
matthew
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