folly/folly/observer/detail/ObserverManager.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 <glog/logging.h>

#include <folly/Portability.h>
#include <folly/experimental/observer/detail/GraphCycleDetector.h>
#include <folly/fibers/FiberManager.h>
#include <folly/functional/Invoke.h>
#include <folly/futures/Future.h>
#include <folly/observer/detail/Core.h>
#include <folly/synchronization/SanitizeThread.h>

namespace folly {
namespace observer_detail {

/**
 * ObserverManager is a singleton which controls the re-computation of all
 * Observers. Such re-computation always happens on the thread pool owned by
 * ObserverManager.
 *
 * ObserverManager has global current version. All existing Observers
 * may have their version be less (yet to be updated) or equal (up to date)
 * to the global current version.
 *
 * ObserverManager::CurrentQueue contains all of the Observers which need to be
 * updated to the global current version. Those updates are peformed on the
 * ObserverManager's thread pool, until the queue is empty. If some Observer is
 * updated, all of its dependents are added to ObserverManager::CurrentQueue
 * to be updated.
 *
 * If some leaf Observer (i.e. created from Observable) is updated, then current
 * version of the ObserverManager should be bumped. All such updated leaf
 * Observers are added to the ObserverManager::NextQueue.
 *
 * *Only* when ObserverManager::CurrentQueue is empty, the global current
 * version is bumped and all updates from the ObserverManager::NextQueue are
 * performed. If leaf Observer gets updated more then once before being picked
 * from the ObserverManager::NextQueue, then only the last update is processed.
 */
class ObserverManager { … };
} // namespace observer_detail
} // namespace folly