Hi Mathieu,
On 4/19/21 5:31 PM, Mathieu Desnoyers wrote:
----- On Apr 19, 2021, at 5:41 AM, Duncan Sands baldr...@free.fr wrote:
Quick question: should we use __atomic_load() or atomic_load_explicit() (C) and
(std::atomic<__typeof__(x)>)(x)).load() (C++) ?
If both are available, is there any advantage to using the C++ version when
compiling C++? As opposed to using the C11 one for both C and C++?
I recently noticed that using C11/C++11 atomic load explicit is not a good
fit for rcu_dereference, because we want the type to be a pointer, not an
_Atomic type. gcc appears to accept a looser typing, but clang has issues
trying to build that code.
in the long run maybe the original variables should be declared with the
appropriate atomic type from the get-go.
So I plan to use __atomic(p, v, __ATOMIC_CONSUME) instead in both C and C++.
Also, I'll drop the cmm_smp_read_barrier_depends() when using __ATOMIC_CONSUME,
because AFAIU their memory ordering semantics are redundant for rcu_dereference.
Yeah, keeping the barrier makes no sense in that case.
Here is the resulting commit for review on gerrit:
https://review.lttng.org/c/userspace-rcu/+/5455 Fix: use __atomic_load() rather
than atomic load explicit [NEW]
Looks good to me (I didn't test it though).
Ciao, Duncan.
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