muduo之LogFile

        muduo之LogFile，LogFile是控制日誌怎麼和文件打交道，其中包含常用的對日誌處理的一些操作。AsyncLogging異步日誌需要調用LogFile的接口將日誌寫入文件,其中包含了AppendFile類，相當於再AppendFile上面封裝了一層。

LogFile.h

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#ifndef MUDUO_BASE_LOGFILE_H
#define MUDUO_BASE_LOGFILE_H

#include "muduo/base/Mutex.h"
#include "muduo/base/Types.h"

#include <memory>

namespace muduo
{

namespace FileUtil
{
class AppendFile;
}

//控制日誌怎樣和文件打交道
class LogFile : noncopyable
{
 public:
  LogFile(const string& basename,
          off_t rollSize,
          bool threadSafe = true,
          int flushInterval = 3,
          int checkEveryN = 1024);
  ~LogFile();

  void append(const char* logline, int len);
  void flush();
  bool rollFile();

 private:
  void append_unlocked(const char* logline, int len);			//不加鎖的append方式

  static string getLogFileName(const string& basename, time_t* now);		  //獲取日誌文件的名稱

  const string basename_;		//日誌文件basename
  const off_t rollSize_;		//日誌文件達到rolsize生成一個新文件
  const int flushInterval_;		//日誌寫入間隔時間
  const int checkEveryN_;	// 每調用checkEveryN_次日誌寫，就滾動一次日誌

  int count_;					// 寫入的次數

  std::unique_ptr<MutexLock> mutex_;	//加鎖
  time_t startOfPeriod_;				//開始記錄日誌時間
  time_t lastRoll_;						//上一次滾動日誌文件時間
  time_t lastFlush_;					//上一次日誌寫入文件時間
  std::unique_ptr<FileUtil::AppendFile> file_;		//文件智能指針

  const static int kRollPerSeconds_ = 60*60*24;		//即時間一天
};

}  // namespace muduo
#endif  // MUDUO_BASE_LOGFILE_H

LogFile.cc

// Use of this source code is governed by a BSD-style license
// that can be found in the License file.
//
// Author: Shuo Chen (chenshuo at chenshuo dot com)

#include "muduo/base/LogFile.h"

#include "muduo/base/FileUtil.h"
#include "muduo/base/ProcessInfo.h"

#include <assert.h>
#include <stdio.h>
#include <time.h>

using namespace muduo;

////控制日誌怎樣和文件打交道
LogFile::LogFile(const string& basename,
                 off_t rollSize,
                 bool threadSafe,
                 int flushInterval,
                 int checkEveryN)
  : basename_(basename),
    rollSize_(rollSize),
    flushInterval_(flushInterval),
    checkEveryN_(checkEveryN),
    count_(0),
    mutex_(threadSafe ? new MutexLock : NULL),		//不是線程安全就不需要構造mutex_
    startOfPeriod_(0),
    lastRoll_(0),
    lastFlush_(0)
{
  assert(basename.find('/') == string::npos);		//斷言basename不包含'/'
  rollFile();
}

LogFile::~LogFile() = default;

void LogFile::append(const char* logline, int len)
{
  if (mutex_)
  {
    MutexLockGuard lock(*mutex_);
    append_unlocked(logline, len);
  }
  else
  {
    append_unlocked(logline, len);
  }
}

void LogFile::flush()
{
  if (mutex_)
  {
    MutexLockGuard lock(*mutex_);
    file_->flush();
  }
  else
  {
    file_->flush();
  }
}

void LogFile::append_unlocked(const char* logline, int len)//不加鎖的append方式
{
  file_->append(logline, len);//AppendFile->append

  if (file_->writtenBytes() > rollSize_)
  {
    rollFile();
  }
  else
  {
    ++count_;
    if (count_ >= checkEveryN_)
    {
      count_ = 0;
      time_t now = ::time(NULL);
      time_t thisPeriod_ = now / kRollPerSeconds_ * kRollPerSeconds_;//比較事件是否相等，不等就是第二天0點，那麼滾動
      if (thisPeriod_ != startOfPeriod_)
      {
        rollFile();
      }
      else if (now - lastFlush_ > flushInterval_)//判斷是否超過flush間隔時間，超過了就flush，否則什麼都不做
      {
        lastFlush_ = now;
        file_->flush();
      }
    }
  }
}

bool LogFile::rollFile()//滾動
{
  time_t now = 0;
  string filename = getLogFileName(basename_, &now);////獲取生成一個文件名稱

  //注意，這裏先除KRollPerSeconds然後乘KPollPerSeconds表示對齊值KRollPerSeconds的整數倍，也就是事件調整到當天零點(/除法會引發取整)
  time_t start = now / kRollPerSeconds_ * kRollPerSeconds_;

  if (now > lastRoll_)
  {
    lastRoll_ = now;
    lastFlush_ = now;
    startOfPeriod_ = start;
    file_.reset(new FileUtil::AppendFile(filename));
    return true;
  }
  return false;
}

string LogFile::getLogFileName(const string& basename, time_t* now)//獲取日誌文件的名稱
{
  string filename;
  filename.reserve(basename.size() + 64);//預分配內存
  filename = basename;

  char timebuf[32];
  struct tm tm;
  *now = time(NULL);
  gmtime_r(now, &tm); // FIXME: localtime_r ?	//獲取當前時間，UTC時間，_r是線程安全
  strftime(timebuf, sizeof timebuf, ".%Y%m%d-%H%M%S.", &tm);//格式化時間，strftime函數
  filename += timebuf;

  filename += ProcessInfo::hostname();

  char pidbuf[32];
  snprintf(pidbuf, sizeof pidbuf, ".%d", ProcessInfo::pid());
  filename += pidbuf;

  filename += ".log";

  return filename;
}