folly/folly/logging/AsyncLogWriter.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 <condition_variable>
#include <mutex>
#include <thread>

#include <folly/File.h>
#include <folly/Range.h>
#include <folly/Synchronized.h>
#include <folly/logging/LogWriter.h>

namespace folly {

/**
 * An abstract LogWriter implementation that provides functionality for
 * asynchronous IO operations. Users can subclass this class and provide their
 * own IO operation implementation by overriding `performIO` method. This class
 * will automatically manage incoming log messages and call the method in
 * appropriate time.
 *
 * This class performs the log I/O in a separarate thread.
 *
 * The advantage of this class over ImmediateFileWriter is that logging I/O can
 * never slow down or block your normal program operation.  If log messages are
 * generated faster than they can be written, messages will be dropped (and an
 * indication of how many messages were dropped will be written to the log file
 * when we are able to catch up a bit.)
 *
 * However, one downside is that if your program crashes, not all log messages
 * may have been written, so you may lose messages generated immediately before
 * the crash.
 */
class AsyncLogWriter : public LogWriter { … };

} // namespace folly