目录
一个轻巧高效的多线程c++stream风格异步日志(二)
前言
本文紧接上一篇文章: 介绍上文中的一条条日志是如何异步导入本地文件的.
首先会简单介绍下LogFile类，之后会具体讲解下AsyncLogging中的双缓冲机制.
整个日志模块的结构图,
LogFile类
LogFile日志文件类 完成日志文件的管理工作.
rollFile() ：滚动文件 当日志超过m_rollSize大小时会滚动一个新的日志文件出来.
getLogFileName() ：用与滚动日志时，给日志文件取名，以滚动时间作为后缀.
m_mutex ：用于append()数据时,给文件上锁.
append() ：黏入日志.
flush() ：冲刷缓冲.
LogFile 有一个AppendFIle类，它是最终用于操作本地文件的类.
append() : 里面会调用系统函数fwrite()写入本地文件.
flush() ： 冲刷缓冲.
writtenBytes() ： 获取已写字节数.
AsyncLogging类
AsyncLogging异步日志类， 完成日志的异步写入工作. 介绍它的接口前,先描述下它的工作逻辑.
AsyncLogging 有以下述几类缓存.
m_currentBuffer : 指向当前接收其他线程append过来的日志的缓存.
m_buffers : 用于存放当前已写满或过了冲刷周期的日志缓存的指针容器.
m_nextBuffer : 指向当m_currentBuffer满后用于替代m_currentBuffer的缓存.
backupBuffer1 : 备用缓存.
backupBuffer2 : 备用缓存.
buffersToWrite : 和m_buffers通过交换swap()后append()到LogFile的指针容器.
AsyncLogging 使用的双缓冲机制 有两个缓存容器 : m_buffers 、buffersToWrite 交替使用 . 一下我们简称为 A 和 B .
A 用于接收 其他线程 append() 进来的日志.
B 用于将目前已接受的缓存 写入 日志文件. 当B写完时 , clean() B , 交换A，B，如此往复.
优点 ： 新建的日志不必等待磁盘操作，也避免了每条新日志都触发日志线程，而是将多条日志拼程一个大的buffer 传送给日志线程写入文件. 相当于批处理， 减少线程唤醒频率 ，降低开销。
另外 ，为了及时将 日志消息写入文件， 即是 buffer A 中还没有push进来日志 也会每三秒 执行一次上述的写入操作.
AsyncLogging使用一个更大的LogBuffer来保存一条条Logger传送过来的日志.
Mutex ：用来控制多线程的写入.
Condition : 用来等待缓冲区中的数据.
Thread : 使用一个线程处理缓存的交换,以及日志的写入.
AsyncLogging实现
下面会给出AsyncLogging的简单实现. 实际上还有几个备用缓存,这里没有加上去,以便于理解程序; 备用缓存主要是为了减少反复new 操作带来的系统开销，
#ifndef _ASYNC_LOGGING_HH
#define _ASYNC_LOGGING_HH
#include "MutexLock.hh"
#include "Thread.hh"
#include "LogStream.hh"
#include "ptr_vector.hh"
#include "Condition.hh"
#include <string>
class AsyncLogging
{
public:
AsyncLogging(const std::string filePath, off_t rollSize, int flushInterval = 3);
~AsyncLogging();
void start(){
m_isRunning = true;
m_thread.start();
}
void stop(){
m_isRunning = false;
m_cond.notify();
}
void append(const char *logline, int len);
private:
AsyncLogging(const AsyncLogging&);
AsyncLogging& operator=(const AsyncLogging&);
void threadRoutine();
typedef LogBuffer<kLargeBuffer> Buffer;
typedef oneself::ptr_vector<Buffer> BufferVector;
typedef oneself::auto_ptr<Buffer> BufferPtr;
const int m_flushInterval;
bool m_isRunning;
off_t m_rollSize;
std::string m_filePath;
Thread m_thread;
MutexLock m_mutex;
Condition m_cond;
BufferPtr m_currentBuffer;
BufferVector m_buffers;
};
#endif
//AsyncLogging.cpp
#include "AsyncLogging.hh"
#include "LogFile.hh"
#include <assert.h>
#include <stdio.h>
AsyncLogging::AsyncLogging(const std::string filePath, off_t rollSize, int flushInterval)
:m_filePath(filePath),
m_rollSize(2048),
m_flushInterval(flushInterval),
m_isRunning(false),
m_thread(std::bind(&AsyncLogging::threadRoutine, this)),
m_mutex(),
m_cond(m_mutex),
m_currentBuffer(new Buffer),
m_buffers()
{
}
AsyncLogging::~AsyncLogging(){
if(m_isRunning) stop();
}
void AsyncLogging::append(const char* logline, int len){
MutexLockGuard lock(m_mutex);
if(m_currentBuffer->avail() > len){
m_currentBuffer->append(logline, len);
}
else{
m_buffers.push_back(m_currentBuffer.release());
m_currentBuffer.reset(new Buffer);
m_currentBuffer->append(logline, len);
m_cond.notify();
}
}
void AsyncLogging::threadRoutine(){
assert(m_isRunning == true);
LogFile output(m_filePath, m_rollSize, false);
BufferVector buffersToWrite;
buffersToWrite.reserve(8);
while(m_isRunning){
assert(buffersToWrite.empty());
{
MutexLockGuard lock(m_mutex);
if(m_buffers.empty()){
m_cond.waitForSeconds(m_flushInterval);
}
m_buffers.push_back(m_currentBuffer.release());
m_currentBuffer.reset(new Buffer);
m_buffers.swap(buffersToWrite);
}
assert(!buffersToWrite.empty());
for(size_t i = 0; i < buffersToWrite.size(); ++i){
output.append(buffersToWrite[i]->data(), buffersToWrite[i]->length());
}
buffersToWrite.clear();
output.flush();
}
output.flush();
}
增加备用缓存
增加备用缓存优化上面程序，上面程序一共在两个地方执行了new操作.
1.m_currentBuffer 填满时，需要把它填进容器的时候.
2.到时间了需要把m_currentBuffer里面的内容写入本地文件时,会把它当前的内容移出来，这时候需要new一个新缓存来给m_currentBuffer.
于是我们准备一个m_nextBuffer来做m_currentBuffer的备用缓存.同时在线程中增加两个backupBuffer 给m_nextBuffer 当备用缓存；当日志量大到不够用的时候, 再考虑用new 操作来动态添加缓存。
#ifndef _ASYNC_LOGGING_HH
#define _ASYNC_LOGGING_HH
#include "MutexLock.hh"
#include "Thread.hh"
#include "LogStream.hh"
#include "ptr_vector.hh"
#include "Condition.hh"
#include <memory>
#include <string>
class AsyncLogging
{
public:
AsyncLogging(const std::string filePath, off_t rollSize, int flushInterval = 3);
~AsyncLogging();
void start(){
m_isRunning = true;
m_thread.start();
}
void stop(){
m_isRunning = false;
m_cond.notify();
}
void append(const char *logline, int len);
private:
AsyncLogging(const AsyncLogging&);
AsyncLogging& operator=(const AsyncLogging&);
void threadRoutine();
typedef LogBuffer<kLargeBuffer> Buffer;
typedef myself::ptr_vector<Buffer> BufferVector;
typedef std::unique_ptr<Buffer> BufferPtr;
const int m_flushInterval;
bool m_isRunning;
off_t m_rollSize;
std::string m_filePath;
Thread m_thread;
MutexLock m_mutex;
Condition m_cond;
BufferPtr m_currentBuffer;
BufferPtr m_nextBuffer;
BufferVector m_buffers;
};
#endif
//AsynvLogging.cpp
#include "AsyncLogging.hh"
#include "LogFile.hh"
#include <assert.h>
#include <stdio.h>
AsyncLogging::AsyncLogging(const std::string filePath, off_t rollSize, int flushInterval)
:m_filePath(filePath),
m_rollSize(rollSize),
m_flushInterval(flushInterval),
m_isRunning(false),
m_thread(std::bind(&AsyncLogging::threadRoutine, this)),
m_mutex(),
m_cond(m_mutex),
m_currentBuffer(new Buffer),
m_nextBuffer(new Buffer),
m_buffers()
{
}
AsyncLogging::~AsyncLogging(){
if(m_isRunning) stop();
}
void AsyncLogging::append(const char* logline, int len){
MutexLockGuard lock(m_mutex);
if(m_currentBuffer->avail() > len){
m_currentBuffer->append(logline, len);
}
else{
m_buffers.push_back(m_currentBuffer.release());
if(m_nextBuffer){
m_currentBuffer = std::move(m_nextBuffer);
}
else{
m_currentBuffer.reset(new Buffer);
}
m_currentBuffer->append(logline, len);
m_cond.notify();
}
}
void AsyncLogging::threadRoutine(){
assert(m_isRunning == true);
LogFile output(m_filePath, m_rollSize, false);
BufferPtr backupBuffer1(new Buffer);
BufferPtr backupBuffer2(new Buffer);
BufferVector buffersToWrite;
buffersToWrite.reserve(8);
while(m_isRunning){
assert(buffersToWrite.empty());
{
MutexLockGuard lock(m_mutex);
if(m_buffers.empty()){
m_cond.waitForSeconds(m_flushInterval);
}
m_buffers.push_back(m_currentBuffer.release());
m_currentBuffer = std::move(backupBuffer1);
m_buffers.swap(buffersToWrite);
if(!m_nextBuffer)
m_nextBuffer = std::move(backupBuffer2);
}
assert(!buffersToWrite.empty());
for(size_t i = 0; i < buffersToWrite.size(); ++i){
output.append(buffersToWrite[i]->data(), buffersToWrite[i]->length());
}
if(buffersToWrite.size() > 2)
{
// drop non-bzero-ed buffers, avoid trashing
buffersToWrite.resize(2);
}
if(!backupBuffer1)
{
assert(!buffersToWrite.empty());
backupBuffer1 = std::move(buffersToWrite.pop_back());
backupBuffer1->reset();
}
if(!backupBuffer2)
{
assert(!buffersToWrite.empty());
backupBuffer2 = std::move(buffersToWrite.pop_back());
backupBuffer2->reset();
}
buffersToWrite.clear();
output.flush();
}
output.flush();
}
结语
本文主要介绍了muduo中AsyncLogging类的实现,其中的双缓存机制. LogFile类及AppendFIle类 分别是日志文件管理类和本地文件的基本操作类. 不难理解，感兴趣的话可以看看muduo的源码，本文不再往下写了，如果想要全部源码可以留言。
作者 —— 艾露米婭娜出处：www.cnblogs.com/ailumiyana/
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