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Change Abseil's SpinLock adaptive_spin_count to a class static variable that can be set by tcmalloc friend classes.

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PiperOrigin-RevId: 826261810
Change-Id: I48eedaf091aff3d9c6b97b7eb8c71958711348cf
This commit is contained in:
Abseil Team
2025-10-30 18:11:40 -07:00
committed by Copybara-Service
parent ed0efc0037
commit 6c5a175774
2 changed files with 7 additions and 24 deletions
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20
absl/base/internal/spinlock.cc
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@@ -71,23 +71,17 @@ void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock,
}
// Monitor the lock to see if its value changes within some time period
// (adaptive_spin_count_ loop iterations). The last value read from the lock
// (adaptive_spin_count loop iterations). The last value read from the lock
// is returned from the method.
ABSL_CONST_INIT std::atomic<int> SpinLock::adaptive_spin_count_{0};
uint32_t SpinLock::SpinLoop() {
// We are already in the slow path of SpinLock, initialize the
// adaptive_spin_count here.
if (adaptive_spin_count_.load(std::memory_order_relaxed) == 0) {
int current_spin_count = 0;
int new_spin_count = NumCPUs() > 1 ? 1000 : 1;
// If this fails, the value will remain unchanged. We may not spin for the
// intended duration, but that is still safe. We will try again on the next
// call to SpinLoop.
adaptive_spin_count_.compare_exchange_weak(
current_spin_count, new_spin_count, std::memory_order_relaxed,
std::memory_order_relaxed);
}
int c = adaptive_spin_count_.load(std::memory_order_relaxed);
ABSL_CONST_INIT static absl::once_flag init_adaptive_spin_count;
ABSL_CONST_INIT static int adaptive_spin_count = 0;
LowLevelCallOnce(&init_adaptive_spin_count,
[]() { adaptive_spin_count = NumCPUs() > 1 ? 1000 : 1; });
int c = adaptive_spin_count;
uint32_t lock_value;
do {
lock_value = lockword_.load(std::memory_order_relaxed);

11
absl/base/internal/spinlock.h
View File

@@ -47,7 +47,6 @@ namespace tcmalloc {
namespace tcmalloc_internal {
class AllocationGuardSpinLockHolder;
class Static;
} // namespace tcmalloc_internal
} // namespace tcmalloc
@@ -174,16 +173,6 @@ class ABSL_LOCKABLE ABSL_ATTRIBUTE_WARN_UNUSED SpinLock {
// Provide access to protected method above. Use for testing only.
friend struct SpinLockTest;
friend class tcmalloc::tcmalloc_internal::AllocationGuardSpinLockHolder;
friend class tcmalloc::tcmalloc_internal::Static;
static int GetAdaptiveSpinCount() {
return adaptive_spin_count_.load(std::memory_order_relaxed);
}
static void SetAdaptiveSpinCount(int count) {
adaptive_spin_count_.store(count, std::memory_order_relaxed);
}
static std::atomic<int> adaptive_spin_count_;
private:
// lockword_ is used to store the following: