- 45b4111d940009bc7b3ebf621c9cb9293c60344a Use copied value i in lambda by Abseil Team <absl-team@google.com>

- b726b3102f8439b8480b6ff52fc3660162fa0bd9 Fix MSVC compiler warning on 32-bit platforms (GitHub iss... by Derek Mauro <dmauro@google.com>
  - a8a29e636c85bd7d82c0cbc824a1c2e498764337 Explicitly forbid to specify the template parameter to Wr... by Abseil Team <absl-team@google.com>
  - 566a1d903266fdbfdcf758401c356a0c6703422d Add missing license header to BUILD file. by Alex Strelnikov <strel@google.com>
  - ef1c0642cde0bbad62bbb30715256b232a4ab817 Fix BUILD file header. by Alex Strelnikov <strel@google.com>
  - b6e2cf00f808ee32b9eb7b3226af79d628742c20 Release GraphCycles microbenchmark. by Alex Strelnikov <strel@google.com>
  - f592d78f549e7a242bf2bb4858a26645a655eac3 Release Mutex microbenchmarks. by Alex Strelnikov <strel@google.com>

GitOrigin-RevId: 45b4111d940009bc7b3ebf621c9cb9293c60344a
Change-Id: I82885ae176952a764574c6d4616e312a977407b2

absl/synchronization/mutex_benchmark.cc

@@ -0,0 +1,96 @@
+// Copyright 2017 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.
+
+#include <vector>
+
+#include "benchmark/benchmark.h"
+#include "absl/base/internal/sysinfo.h"
+#include "absl/synchronization/blocking_counter.h"
+#include "absl/synchronization/internal/thread_pool.h"
+#include "absl/synchronization/mutex.h"
+
+namespace {
+
+// Measure the overhead of conditions on mutex release (when they must be
+// evaluated).  Mutex has (some) support for equivalence classes allowing
+// Conditions with the same function/argument to potentially not be multiply
+// evaluated.
+//
+// num_classes==0 is used for the special case of every waiter being distinct.
+void BM_ConditionWaiters(benchmark::State& state) {
+  int num_classes = state.range(0);
+  int num_waiters = state.range(1);
+
+  struct Helper {
+    static void Waiter(absl::BlockingCounter* init, absl::Mutex* m, int* p) {
+      init->DecrementCount();
+      m->LockWhen(absl::Condition(
+          static_cast<bool (*)(int*)>([](int* v) { return *v == 0; }), p));
+      m->Unlock();
+    }
+  };
+
+  if (num_classes == 0) {
+    // No equivalence classes.
+    num_classes = num_waiters;
+  }
+
+  absl::BlockingCounter init(num_waiters);
+  absl::Mutex mu;
+  std::vector<int> equivalence_classes(num_classes, 1);
+
+  // Must be declared last to be destroyed first.
+  absl::synchronization_internal::ThreadPool pool(num_waiters);
+
+  for (int i = 0; i < num_waiters; i++) {
+    // Mutex considers Conditions with the same function and argument
+    // to be equivalent.
+    pool.Schedule([&, i] {
+      Helper::Waiter(&init, &mu, &equivalence_classes[i % num_classes]);
+    });
+  }
+  init.Wait();
+
+  for (auto _ : state) {
+    mu.Lock();
+    mu.Unlock();  // Each unlock requires Condition evaluation for our waiters.
+  }
+
+  mu.Lock();
+  for (int i = 0; i < num_classes; i++) {
+    equivalence_classes[i] = 0;
+  }
+  mu.Unlock();
+}
+
+#ifdef THREAD_SANITIZER
+// ThreadSanitizer can't handle 8192 threads.
+constexpr int kMaxConditionWaiters = 2048;
+#else
+constexpr int kMaxConditionWaiters = 8192;
+#endif
+BENCHMARK(BM_ConditionWaiters)->RangePair(0, 2, 1, kMaxConditionWaiters);
+
+void BM_ContendedMutex(benchmark::State& state) {
+  static absl::Mutex* mu = new absl::Mutex;
+  for (auto _ : state) {
+    absl::MutexLock lock(mu);
+  }
+}
+BENCHMARK(BM_ContendedMutex)->Threads(1);
+BENCHMARK(BM_ContendedMutex)->ThreadPerCpu();
+
+}  // namespace
+
+BENCHMARK_MAIN();