3 files changed, 82 insertions, 2 deletions
diff --git a/absl/base/BUILD.bazel b/absl/base/BUILD.bazel
index 44de05e3e094..4566c697cfdd 100644
--- a/absl/base/BUILD.bazel
+++ b/absl/base/BUILD.bazel
@@ -107,6 +107,7 @@ cc_library(
         "internal/identity.h",
         "internal/inline_variable.h",
         "internal/invoke.h",
+        "internal/scheduling_mode.h",
     ],
     copts = ABSL_DEFAULT_COPTS,
     visibility = [
@@ -314,6 +315,33 @@ cc_test(
 )
 
 cc_library(
+    name = "spinlock_benchmark_common",
+    testonly = 1,
+    srcs = ["internal/spinlock_benchmark.cc"],
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = [
+        "//absl/base:__pkg__",
+    ],
+    deps = [
+        ":base",
+        ":base_internal",
+        "//absl/synchronization",
+        "@com_github_google_benchmark//:benchmark_main",
+    ],
+    alwayslink = 1,
+)
+
+cc_binary(
+    name = "spinlock_benchmark",
+    testonly = 1,
+    copts = ABSL_DEFAULT_COPTS,
+    visibility = ["//visibility:private"],
+    deps = [
+        ":spinlock_benchmark_common",
+    ],
+)
+
+cc_library(
     name = "endian",
     hdrs = [
         "internal/endian.h",
diff --git a/absl/base/internal/spinlock.h b/absl/base/internal/spinlock.h
index dcce01092235..eb3eec9cd0a1 100644
--- a/absl/base/internal/spinlock.h
+++ b/absl/base/internal/spinlock.h
@@ -101,8 +101,8 @@ class LOCKABLE SpinLock {
   inline void Unlock() UNLOCK_FUNCTION() {
     ABSL_TSAN_MUTEX_PRE_UNLOCK(this, 0);
     uint32_t lock_value = lockword_.load(std::memory_order_relaxed);
-    lockword_.store(lock_value & kSpinLockCooperative,
-                    std::memory_order_release);
+    lock_value = lockword_.exchange(lock_value & kSpinLockCooperative,
+                                    std::memory_order_release);
 
     if ((lock_value & kSpinLockDisabledScheduling) != 0) {
       base_internal::SchedulingGuard::EnableRescheduling(true);
diff --git a/absl/base/internal/spinlock_benchmark.cc b/absl/base/internal/spinlock_benchmark.cc
new file mode 100644
index 000000000000..907d3e2745b3
--- /dev/null
+++ b/absl/base/internal/spinlock_benchmark.cc
@@ -0,0 +1,52 @@
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// See also //absl/synchronization:mutex_benchmark for a comparison of SpinLock
+// and Mutex performance under varying levels of contention.
+
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/scheduling_mode.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/synchronization/internal/create_thread_identity.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+template <absl::base_internal::SchedulingMode scheduling_mode>
+static void BM_SpinLock(benchmark::State& state) {
+  // Ensure a ThreadIdentity is installed.
+  ABSL_INTERNAL_CHECK(
+      absl::synchronization_internal::GetOrCreateCurrentThreadIdentity() !=
+          nullptr,
+      "GetOrCreateCurrentThreadIdentity() failed");
+
+  static auto* spinlock = new absl::base_internal::SpinLock(scheduling_mode);
+  for (auto _ : state) {
+    absl::base_internal::SpinLockHolder holder(spinlock);
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_KERNEL_ONLY)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+BENCHMARK_TEMPLATE(BM_SpinLock,
+                   absl::base_internal::SCHEDULE_COOPERATIVE_AND_KERNEL)
+    ->UseRealTime()
+    ->Threads(1)
+    ->ThreadPerCpu();
+
+}  // namespace