On Sat, Oct 27, 2018 at 12:03:25AM +0800, Junchang Wang wrote:
> If the 4th parameter (field *weak*) of __atomic_compare_exchange_n is set, it
> may refuse to perform the CAS operation and return a failure, even if the value
> of field *old* is equal to the content of the specified memory location. This
> happens in architectures where LL/SC is used to emulate CAS primitive (e.g., PPC
> and ARM).
>
> This patch returns the *old* value if __atomic_compare_exchange_n has been
> successfully performed; otherwise, *old*+1 is returned, which forces the caller
> to retry the CAS loop.
>
> Signed-off-by: Junchang Wang <junchangwang@xxxxxxxxx>
> Signed-off-by: kira Yokosawa <akiyks@xxxxxxxxx>
Very good, queued and pushed with adjustments to the commit log above,
thank you!!!
Please let me know if further adjustments are required.
Thanx, Paul
> ---
> CodeSamples/api-pthreads/api-gcc.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/CodeSamples/api-pthreads/api-gcc.h b/CodeSamples/api-pthreads/api-gcc.h
> index 1dd26ca..3afe340 100644
> --- a/CodeSamples/api-pthreads/api-gcc.h
> +++ b/CodeSamples/api-pthreads/api-gcc.h
> @@ -168,9 +168,8 @@ struct __xchg_dummy {
> ({ \
> typeof(*ptr) _____actual = (o); \
> \
> - (void)__atomic_compare_exchange_n(ptr, (void *)&_____actual, (n), 1, \
> - __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST); \
> - _____actual; \
> + __atomic_compare_exchange_n(ptr, (void *)&_____actual, (n), 1, \
> + __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST) ? (o) : (o)+1; \
> })
>
> static __inline__ int atomic_cmpxchg(atomic_t *v, int old, int new)
> --
> 2.7.4
>
