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(Roll forward) 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: 826545231
Change-Id: Ic8918fdc0ebd46ea0423859ed62d667f7fe0ba57
This commit is contained in:
Connal de Souza
2025-10-31 10:40:01 -07:00
committed by Copybara-Service
parent 6c5a175774
commit 982f4254a1
2 changed files with 24 additions and 7 deletions
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20
absl/base/internal/spinlock.cc
View File

@@ -71,17 +71,23 @@ 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.
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;
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);
uint32_t lock_value;
do {
lock_value = lockword_.load(std::memory_order_relaxed);

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

@@ -47,6 +47,7 @@ namespace tcmalloc {
namespace tcmalloc_internal {
class AllocationGuardSpinLockHolder;
class Static;
} // namespace tcmalloc_internal
} // namespace tcmalloc
@@ -173,6 +174,16 @@ 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: