Implementation of Muduo asynchronous logging

Catalog

One 、 Log level and format

Two 、 The destination of the log

3、 ... and 、 Multithreaded asynchronous log implementation

（1） characteristic

（2） Concrete realization

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muduo It's for Chen Shuo's personal use C++ Developed a network library , The code is of great learning value , The summary comes from books 《Linux Multithreaded server-side programming 》, Also written by Chen Shuo , Can cooperate with github Use code together .

muduo github website ：https://github.com/chenshuo/muduo

One 、 Log level and format

TRACE、DEBUG、INFO、WARN、ERROR、FATAL, The default level is obtained from the environment variable , To adjust the level, you only need to call Logger::setLogLevel() that will do ;

muduo The format of the log message is as follows ：

The date and time in the timestamp string are cached , Multiple logs within one second only need to reformat the microsecond part .

Two 、 The destination of the log

Write to a local file .

Rolling condition ： File size and time , For program crash , The log cannot flush To hard disk ,muduo On a regular basis （ every other 3 second ） Log the buffer flush To hard disk , And every log message in memory has cookie( The address of a function ), This can be done in core dump Find in the file cookie You can find messages that haven't been written to the disk yet .

3、 ... and 、 Multithreaded asynchronous log implementation

（1） characteristic

Each process writes only one log file , Use a background thread to collect log information , And write the log file , Other business threads just send log messages to this background thread .

（2） Concrete realization

Double buffering technology ： Prepare two pieces buffer,A、B, The front end is responsible for buffer A Fill in the data , The back end is responsible for buffer B The data for is written to the file , When buffer A After full , In exchange for A and B, Let the back end bufferA The data for is written to the file , The front end continues bufferB Fill in the new message , So back and forth .

In order to write the log to the file in time , Even if buffer A Not full , Also every 3 Seconds for swap write operation .

When the front-end write frequency is not high ：

When the front-end write frequency is high ：

Front end write frequency is too high , When messages are dense ：