--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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.
+ */
+
+/*
+ * Drop-in replacement for std::call_once() with a fast path, which the GCC
+ * implementation lacks. The tradeoff is a slightly larger `once_flag' struct
+ * (8 bytes vs 4 bytes with GCC on Linux/x64).
+ *
+ * $ call_once_test --benchmark --bm_min_iters=100000000 --threads=16
+ * ============================================================================
+ * folly/test/CallOnceTest.cpp relative time/iter iters/s
+ * ============================================================================
+ * StdCallOnceBench 3.54ns 282.82M
+ * FollyCallOnceBench 698.48ps 1.43G
+ * ============================================================================
+ */
+
+#pragma once
+
+#include <atomic>
+#include <mutex>
+#include <utility>
+
+#include <folly/Likely.h>
+#include <folly/Portability.h>
+
+namespace folly {
+
+class once_flag {
+ public:
+ constexpr once_flag() noexcept = default;
+ once_flag(const once_flag&) = delete;
+ once_flag& operator=(const once_flag&) = delete;
+
+ template <typename Callable, class... Args>
+ friend void call_once(once_flag& flag, Callable&& f, Args&&... args);
+ template <typename Callable, class... Args>
+ friend void call_once_impl_no_inline(once_flag& flag,
+ Callable&& f,
+ Args&&... args);
+
+ private:
+ std::atomic<bool> called_{false};
+ std::once_flag std_once_flag_;
+};
+
+template <class Callable, class... Args>
+void FOLLY_ALWAYS_INLINE
+call_once(once_flag& flag, Callable&& f, Args&&... args) {
+ if (LIKELY(flag.called_.load(std::memory_order_acquire))) {
+ return;
+ }
+ call_once_impl_no_inline(
+ flag, std::forward<Callable>(f), std::forward<Args>(args)...);
+}
+
+// Implementation detail: out-of-line slow path
+template <class Callable, class... Args>
+void FOLLY_NOINLINE
+call_once_impl_no_inline(once_flag& flag, Callable&& f, Args&&... args) {
+ std::call_once(flag.std_once_flag_,
+ std::forward<Callable>(f),
+ std::forward<Args>(args)...);
+ flag.called_.store(true, std::memory_order_release);
+}
+}
Baton.h \
Benchmark.h \
Bits.h \
+ CallOnce.h \
Checksum.h \
ConcurrentSkipList.h \
ConcurrentSkipList-inl.h \
#include <array>
#include <glog/logging.h>
+#include <folly/CallOnce.h>
#include <folly/File.h>
#include <folly/FileUtil.h>
#include <folly/ThreadLocal.h>
void readRandomDevice(void* data, size_t size) {
#ifdef _MSC_VER
- static std::once_flag flag;
+ static folly::once_flag flag;
static HCRYPTPROV cryptoProv;
- std::call_once(flag, [&] {
+ folly::call_once(flag, [&] {
PCHECK(CryptAcquireContext(&cryptoProv, nullptr, nullptr,
PROV_RSA_FULL, 0));
});
#include <condition_variable>
#include <mutex>
#include <boost/intrusive/list.hpp>
+#include <folly/CallOnce.h>
#include <folly/Hash.h>
#include <folly/ScopeGuard.h>
static const size_t kNumBuckets = 4096;
static EmulatedFutexBucket* gBuckets;
- static std::once_flag gBucketInit;
+ static folly::once_flag gBucketInit;
static EmulatedFutexBucket& bucketFor(void* addr) {
- std::call_once(gBucketInit, [](){
+ folly::call_once(gBucketInit, [](){
gBuckets = new EmulatedFutexBucket[kNumBuckets];
});
uint64_t mixedBits = folly::hash::twang_mix64(
};
EmulatedFutexBucket* EmulatedFutexBucket::gBuckets;
-std::once_flag EmulatedFutexBucket::gBucketInit;
+folly::once_flag EmulatedFutexBucket::gBucketInit;
int emulatedFutexWake(void* addr, int count, uint32_t waitMask) {
auto& bucket = EmulatedFutexBucket::bucketFor(addr);
--- /dev/null
+/*
+ * Copyright 2016 Facebook, Inc.
+ *
+ * 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 <deque>
+#include <mutex>
+#include <thread>
+
+#include <folly/Benchmark.h>
+#include <folly/CallOnce.h>
+#include <gflags/gflags.h>
+#include <glog/logging.h>
+#include <gtest/gtest.h>
+
+DEFINE_int32(threads, 16, "benchmark concurrency");
+
+template <typename CallOnceFunc>
+void bm_impl(CallOnceFunc&& fn, int64_t iters) {
+ std::deque<std::thread> threads;
+ for (int i = 0; i < FLAGS_threads; ++i) {
+ threads.emplace_back([&fn, iters] {
+ for (int64_t j = 0; j < iters; ++j) {
+ fn();
+ }
+ });
+ }
+ for (std::thread& t : threads) {
+ t.join();
+ }
+}
+
+BENCHMARK(StdCallOnceBench, iters) {
+ std::once_flag flag;
+ int out = 0;
+ bm_impl([&] { std::call_once(flag, [&] { ++out; }); }, iters);
+ ASSERT_EQ(1, out);
+}
+
+BENCHMARK(FollyCallOnceBench, iters) {
+ folly::once_flag flag;
+ int out = 0;
+ bm_impl([&] { folly::call_once(flag, [&] { ++out; }); }, iters);
+ ASSERT_EQ(1, out);
+}
+
+TEST(FollyCallOnce, Simple) {
+ folly::once_flag flag;
+ auto fn = [&](int* outp) { ++*outp; };
+ int out = 0;
+ folly::call_once(flag, fn, &out);
+ folly::call_once(flag, fn, &out);
+ ASSERT_EQ(1, out);
+}
+
+TEST(FollyCallOnce, Stress) {
+ for (int i = 0; i < 100; ++i) {
+ folly::once_flag flag;
+ int out = 0;
+ bm_impl([&] { folly::call_once(flag, [&] { ++out; }); }, 100);
+ ASSERT_EQ(1, out);
+ }
+}
+
+int main(int argc, char** argv) {
+ testing::InitGoogleTest(&argc, argv);
+ gflags::ParseCommandLineFlags(&argc, &argv, true);
+ if (FLAGS_benchmark) {
+ folly::runBenchmarksOnFlag();
+ return 0;
+ } else {
+ return RUN_ALL_TESTS();
+ }
+}
projects / folly.git / commitdiff