folly/folly/concurrency/memory/AtomicReadMostlyMainPtr.h

/*
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * 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.
 */

#pragma once

#include <atomic>
#include <cstdint>
#include <memory>
#include <mutex>

#include <folly/Indestructible.h>
#include <folly/concurrency/memory/ReadMostlySharedPtr.h>
#include <folly/synchronization/Rcu.h>

namespace folly {

namespace detail {
extern Indestructible<std::mutex> atomicReadMostlyMu;
extern Indestructible<rcu_domain> atomicReadMostlyDomain;
} // namespace detail

/*
 * What atomic_shared_ptr is to shared_ptr, AtomicReadMostlyMainPtr is to
 * ReadMostlyMainPtr; it allows racy conflicting accesses to one. This gives
 * true shared_ptr-like semantics, including reclamation at the point where the
 * last pointer to an object goes away.
 *
 * It's about the same speed (slightly slower) as ReadMostlyMainPtr. The most
 * significant feature they share is avoiding reader-reader contention and
 * atomic RMWs in the absence of writes.
 */
template <typename T>
class AtomicReadMostlyMainPtr { … };

} // namespace folly