Add 'third_party/abseil_cpp/' from commit '768eb2ca2857342673fcd462792ce04b8bac3fa3' r/781

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54beb5796cd408fbe15d2d2da09ff37adf
git-subtree-split: 768eb2ca2857342673fcd462792ce04b8bac3fa3

1 files changed, 223 insertions, 0 deletions

diff --git a/third_party/abseil_cpp/absl/synchronization/mutex_benchmark.cc b/third_party/abseil_cpp/absl/synchronization/mutex_benchmark.cc
new file mode 100644
index 0000000000..ab1880012a
--- /dev/null
+++ b/third_party/abseil_cpp/absl/synchronization/mutex_benchmark.cc
@@ -0,0 +1,223 @@
+// 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
+//
+//      https://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 <cstdint>
+#include <mutex>  // NOLINT(build/c++11)
+#include <vector>
+
+#include "absl/base/internal/cycleclock.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/synchronization/blocking_counter.h"
+#include "absl/synchronization/internal/thread_pool.h"
+#include "absl/synchronization/mutex.h"
+#include "benchmark/benchmark.h"
+
+namespace {
+
+void BM_Mutex(benchmark::State& state) {
+  static absl::Mutex* mu = new absl::Mutex;
+  for (auto _ : state) {
+    absl::MutexLock lock(mu);
+  }
+}
+BENCHMARK(BM_Mutex)->UseRealTime()->Threads(1)->ThreadPerCpu();
+
+static void DelayNs(int64_t ns, int* data) {
+  int64_t end = absl::base_internal::CycleClock::Now() +
+                ns * absl::base_internal::CycleClock::Frequency() / 1e9;
+  while (absl::base_internal::CycleClock::Now() < end) {
+    ++(*data);
+    benchmark::DoNotOptimize(*data);
+  }
+}
+
+template <typename MutexType>
+class RaiiLocker {
+ public:
+  explicit RaiiLocker(MutexType* mu) : mu_(mu) { mu_->Lock(); }
+  ~RaiiLocker() { mu_->Unlock(); }
+ private:
+  MutexType* mu_;
+};
+
+template <>
+class RaiiLocker<std::mutex> {
+ public:
+  explicit RaiiLocker(std::mutex* mu) : mu_(mu) { mu_->lock(); }
+  ~RaiiLocker() { mu_->unlock(); }
+ private:
+  std::mutex* mu_;
+};
+
+template <typename MutexType>
+void BM_Contended(benchmark::State& state) {
+  struct Shared {
+    MutexType mu;
+    int data = 0;
+  };
+  static auto* shared = new Shared;
+  int local = 0;
+  for (auto _ : state) {
+    // Here we model both local work outside of the critical section as well as
+    // some work inside of the critical section. The idea is to capture some
+    // more or less realisitic contention levels.
+    // If contention is too low, the benchmark won't measure anything useful.
+    // If contention is unrealistically high, the benchmark will favor
+    // bad mutex implementations that block and otherwise distract threads
+    // from the mutex and shared state for as much as possible.
+    // To achieve this amount of local work is multiplied by number of threads
+    // to keep ratio between local work and critical section approximately
+    // equal regardless of number of threads.
+    DelayNs(100 * state.threads, &local);
+    RaiiLocker<MutexType> locker(&shared->mu);
+    DelayNs(state.range(0), &shared->data);
+  }
+}
+
+BENCHMARK_TEMPLATE(BM_Contended, absl::Mutex)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
+BENCHMARK_TEMPLATE(BM_Contended, absl::base_internal::SpinLock)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
+BENCHMARK_TEMPLATE(BM_Contended, std::mutex)
+    ->UseRealTime()
+    // ThreadPerCpu poorly handles non-power-of-two CPU counts.
+    ->Threads(1)
+    ->Threads(2)
+    ->Threads(4)
+    ->Threads(6)
+    ->Threads(8)
+    ->Threads(12)
+    ->Threads(16)
+    ->Threads(24)
+    ->Threads(32)
+    ->Threads(48)
+    ->Threads(64)
+    ->Threads(96)
+    ->Threads(128)
+    ->Threads(192)
+    ->Threads(256)
+    // Some empirically chosen amounts of work in critical section.
+    // 1 is low contention, 200 is high contention and few values in between.
+    ->Arg(1)
+    ->Arg(20)
+    ->Arg(50)
+    ->Arg(200);
+
+// 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();
+}
+
+// Some configurations have higher thread limits than others.
+#if defined(__linux__) && !defined(THREAD_SANITIZER)
+constexpr int kMaxConditionWaiters = 8192;
+#else
+constexpr int kMaxConditionWaiters = 1024;
+#endif
+BENCHMARK(BM_ConditionWaiters)->RangePair(0, 2, 1, kMaxConditionWaiters);
+
+}  // namespace