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[libc++] Use native wait in std::barrier instead of sleep loop (#171041)

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For some reason, the current `std::barrier`'s wait implementation polls
the underlying atomic in a loop with sleeps instead of using the native
wait.

This change should also indirectly fix the performance issue of
`std::barrier` described in
https://github.com/llvm/llvm-project/issues/123855.

Fixes #123855
This commit is contained in:
Hui 2025-12-14 09:34:57 +00:00 committed by GitHub
parent 86dc131997
commit 8680feb913
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1 changed files with 1 additions and 4 deletions
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5
libcxx/include/barrier
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@ -57,8 +57,6 @@ namespace std
# include <__atomic/memory_order.h>
# include <__cstddef/ptrdiff_t.h>
# include <__memory/unique_ptr.h>
# include <__thread/poll_with_backoff.h>
# include <__thread/timed_backoff_policy.h>
# include <__utility/move.h>
# include <cstdint>
# include <limits>
@ -142,8 +140,7 @@ public:
return __old_phase;
}
_LIBCPP_HIDE_FROM_ABI void wait(arrival_token&& __old_phase) const {
auto const __test_fn = [this, __old_phase]() -> bool { return __phase_.load(memory_order_acquire) != __old_phase; };
std::__libcpp_thread_poll_with_backoff(__test_fn, __libcpp_timed_backoff_policy());
__phase_.wait(__old_phase, std::memory_order_acquire);
}
_LIBCPP_HIDE_FROM_ABI void arrive_and_drop() {
__expected_adjustment_.fetch_sub(1, memory_order_relaxed);