/* * Copyright (c) Facebook, Inc. and its 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 #include namespace folly { class LogCategory; class LogHandlerConfig; class LogMessage; /** * LogHandler represents a generic API for processing log messages. * * LogHandlers have an associated log level. The LogHandler will discard any * messages below its log level. This allows specific LogHandlers to perform * additional filtering of messages even if the messages were enabled at the * LogCategory level. For instance, a single LogCategory may have two * LogHandlers attached, one that logs locally to a file, and one that sends * messages to a remote logging service. The local LogHandler may be * configured to record all messages, but the remote LogHandler may want to * only process ERROR messages and above, even when debug logging is enabled * for this LogCategory. * * By default the LogHandler level is set to LogLevel::NONE, which means that * all log messages will be processed. */ class LogHandler { public: virtual ~LogHandler() = default; /** * handleMessage() is called when a log message is processed by a LogCategory * that this handler is attached to. * * This must be implemented by LogHandler subclasses. * * handleMessage() will always be invoked from the thread that logged the * message. LogMessage::getThreadID() contains the thread ID, but the * LogHandler can also include any other thread-local state they desire, and * this will always be data for the thread that originated the log message. * * @param message The LogMessage objet. * @param handlerCategory The LogCategory that invoked handleMessage(). * This is the category that this LogHandler is attached to. Note that * this may be different than the category that this message was * originally logged at. message->getCategory() returns the category of * the log message. */ virtual void handleMessage( const LogMessage& message, const LogCategory* handlerCategory) = 0; /** * Block until all messages that have already been sent to this LogHandler * have been processed. * * For LogHandlers that perform asynchronous processing of log messages, * this ensures that messages already sent to this handler have finished * being processed. * * Other threads may still call handleMessage() while flush() is running. * handleMessage() calls that did not complete before the flush() call * started will not necessarily be processed by the flush call. */ virtual void flush() = 0; /** * Return a LogHandlerConfig object describing the configuration of this * LogHandler. */ virtual LogHandlerConfig getConfig() const = 0; }; } // namespace folly