move CallOnce to synchronization/

[folly.git] / folly / CallOnce.h

diff --git a/folly/CallOnce.h b/folly/CallOnce.h
deleted file mode 100644 (file)
index 4dd0694..0000000
--- a/folly/CallOnce.h
+++ /dev/null
@@ -1,84 +0,0 @@
-/*
- * Copyright 2017 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>
-#include <folly/SharedMutex.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};
-  folly::SharedMutex mutex_;
-};
-
-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::lock_guard<folly::SharedMutex> lg(flag.mutex_);
-  if (flag.called_) {
-    return;
-  }
-
-  std::forward<Callable>(f)(std::forward<Args>(args)...);
-
-  flag.called_.store(true, std::memory_order_release);
-}
-}