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// 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
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