- abacaab4b11a69dd4db627bd183571d7cabb8def Refinement to previous time.h edit (in this same github p... by Greg Falcon <gfalcon@google.com>

  - 64db19b773134c6c8004e3b23c9ca892efbf8bae Move SpinLock's adaptive spin count computation from a st... by Derek Mauro <dmauro@google.com>
  - 6f9533fb44a52485a7c2bbb9b4efc7bf8d6c359a Import of CCTZ from GitHub. by Abseil Team <absl-team@google.com>
  - a211d7255c986e8dd4ceada362c0d054a6a1969a Cleanup exception flags by Abseil Team <absl-team@google.com>
  - babdb29c590126fe9bba5229fe91034b5b5c358a Release time benchmarks. by Alex Strelnikov <strel@google.com>
  - 5803b32a3ff123d1fb57a0c471d199c818357c9f Release memutil microbenchmarks. by Alex Strelnikov <strel@google.com>
  - 5357d4890d30e80c53beb05af32500fb20e9402b Add parens around expansion of ABSL_PREDICT_{FALSE,TRUE} ... by Abseil Team <absl-team@google.com>
  - 32023f61a239a5f6b1c59e577bfe81b179bbcd2d Reformat build rule tag. by Alex Strelnikov <strel@google.com>
  - 833758ecf2b0cf7a42bbd50b5b127e416425c168 Release uint128 microbenchmarks. by Alex Strelnikov <strel@google.com>
  - c115a9bca1f944b90fdc78a56b2de176466b124f Disambiguate bitwise-not of size_type by Abseil Team <absl-team@google.com>
  - f6905f5b5f6e425792de646edafde440548d9346 Updates ConstructorTracker and TrackedObjects with 1) a m... by Abseil Team <absl-team@google.com>
  - 147c553bdd5d2db20a38f75c4d1ef973d6c709c5 Changes the absl::Duration factory functions to disallow ... by Greg Miller <jgm@google.com>
  - dba2b96d11b5264546b283ba452f2de1303b0f07 White space fix by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: abacaab4b11a69dd4db627bd183571d7cabb8def
Change-Id: I6fa34f20d0b2f898e7b5475a603111413bb80a67

1 files changed, 10 insertions, 20 deletions

diff --git a/absl/base/internal/spinlock.cc b/absl/base/internal/spinlock.cc
index 28a2059f3287..1b97efbccc58 100644
--- a/absl/base/internal/spinlock.cc
+++ b/absl/base/internal/spinlock.cc
@@ -18,10 +18,12 @@
 #include <atomic>
 #include <limits>
 
+#include "absl/base/attributes.h"
 #include "absl/base/internal/atomic_hook.h"
 #include "absl/base/internal/cycleclock.h"
 #include "absl/base/internal/spinlock_wait.h"
 #include "absl/base/internal/sysinfo.h" /* For NumCPUs() */
+#include "absl/base/call_once.h"
 
 // Description of lock-word:
 //  31..00: [............................3][2][1][0]
@@ -54,30 +56,10 @@
 namespace absl {
 namespace base_internal {
 
-static int adaptive_spin_count = 0;
-
-namespace {
-struct SpinLock_InitHelper {
-  SpinLock_InitHelper() {
-    // On multi-cpu machines, spin for longer before yielding
-    // the processor or sleeping.  Reduces idle time significantly.
-    if (base_internal::NumCPUs() > 1) {
-      adaptive_spin_count = 1000;
-    }
-  }
-};
-
-// Hook into global constructor execution:
-// We do not do adaptive spinning before that,
-// but nothing lock-intensive should be going on at that time.
-static SpinLock_InitHelper init_helper;
-
 ABSL_CONST_INIT static base_internal::AtomicHook<void (*)(const void *lock,
                                                           int64_t wait_cycles)>
     submit_profile_data;
 
-}  // namespace
-
 void RegisterSpinLockProfiler(void (*fn)(const void *contendedlock,
                                          int64_t wait_cycles)) {
   submit_profile_data.Store(fn);
@@ -120,6 +102,14 @@ void SpinLock::InitLinkerInitializedAndCooperative() {
 // from the lock is returned from the method.
 uint32_t SpinLock::SpinLoop(int64_t initial_wait_timestamp,
                             uint32_t *wait_cycles) {
+  // 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;
+  base_internal::LowLevelCallOnce(&init_adaptive_spin_count, []() {
+    adaptive_spin_count = base_internal::NumCPUs() > 1 ? 1000 : 1;
+  });
+
   int c = adaptive_spin_count;
   uint32_t lock_value;
   do {