folly/folly/io/async/EventBasePoller.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 <chrono>
#include <memory>

#include <folly/Function.h>
#include <folly/Range.h>
#include <folly/Synchronized.h>

namespace folly::detail {

/**
 * EventBasePoller centralizes the blocking wait for events across multiple
 * EventBases in a process. The singleton calls the provided ReadyCallback on
 * ready EventBases, so they can be driven without blocking. This enables
 * control over which threads drive the EventBases, as opposed to the standard
 * blocking loop that requires one thread per EventBase.
 *
 * EventBases' pollable fds are registered in groups, so that the callback can
 * batch processing of ready EventBases that belong to the same group.
 *
 * When the EventBase is ready it can be driven until it would block again, and
 * then handoff() must be called to resume polling the fd. Neither the driving
 * of the EventBase or the call to handoff() should happen inline in the
 * callback, but delegated to another thread without blocking; the callback must
 * return control quickly, as it executes in the main polling loop and can slow
 * down the handling of all other registered EventBases.
 *
 * Note that none of the implementation is specific to EventBases, in fact this
 * is a lightweight implementation of an event loop specialized on polling read
 * events, and which supports grouping of the fds for batch-handling. The class
 * could be easily generalized if other applications arise.
 */
class EventBasePoller { … };

} // namespace folly::detail