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Stop using sleep timeouts for Linux futex-based SpinLock

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Timeouts were once necessary when the SpinLock Unlock used an atomic
store and could therefore have a race and a missed wakeup, however,
the Unlock path now uses an atomic exchange, so the missed wakeup
cannot happen.

Fixes #1179

PiperOrigin-RevId: 452047517
Change-Id: I844944879b51b7f7ddac148e063a376cddd0d05a
This commit is contained in:
Derek Mauro
2022-05-31 08:00:22 -07:00
committed by Copybara-Service
parent ea78ded7a5
commit a4cc270df1
1 changed files with 2 additions and 5 deletions
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7
absl/base/internal/spinlock_linux.inc
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@@ -57,13 +57,10 @@ static_assert(sizeof(std::atomic<uint32_t>) == sizeof(int),
extern "C" {
ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockDelay)(
std::atomic<uint32_t> *w, uint32_t value, int loop,
std::atomic<uint32_t> *w, uint32_t value, int,
absl::base_internal::SchedulingMode) {
absl::base_internal::ErrnoSaver errno_saver;
struct timespec tm;
tm.tv_sec = 0;
tm.tv_nsec = absl::base_internal::SpinLockSuggestedDelayNS(loop);
syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, &tm);
syscall(SYS_futex, w, FUTEX_WAIT | FUTEX_PRIVATE_FLAG, value, nullptr);
}
ABSL_ATTRIBUTE_WEAK void ABSL_INTERNAL_C_SYMBOL(AbslInternalSpinLockWake)(