muduo网络库源码学习————Timestamp.cc

今天开始学习陈硕先生的muduo网络库，moduo网络库得到很多好评，陈硕先生自己也说核心代码不超过5000行，所以我觉得有必要拿过来好好学习下，学习的时候在源码上面添加一些自己的注释，方便日后理解，首先看看UTC时间戳，源码目录为base文件夹：
Timestamp.h

//UTC时间戳 
//类声明文件
#ifndef MUDUO_BASE_TIMESTAMP_H
#define MUDUO_BASE_TIMESTAMP_H

#include <muduo/base/copyable.h>
#include <muduo/base/Types.h>

#include <boost/operators.hpp>

namespace muduo
{
// Time stamp in UTC, in microseconds resolution.
//时间起始点是1970 1月1号0:0:0
// This class is immutable.
// It's recommended to pass it by value, since it's passed in register on x64.
//继承两个类
//muduo::copyable空基类，标识类，值类型
//boost::less_than_comparable<Timestamp>要求实现< 号运算符
//可自动实现>,<=,>=
//这是一种模板语言编程思想
class Timestamp : public muduo::copyable, public boost::less_than_comparable<Timestamp>
{
 public:
  //
  // Constucts an invalid Timestamp.
  //
  Timestamp(): microSecondsSinceEpoch_(0)
  {
  }
  // Constucts a Timestamp at specific time
  // @param microSecondsSinceEpoch
  explicit Timestamp(int64_t microSecondsSinceEpoch);
//两个时间戳进行交换
  void swap(Timestamp& that)
  {
    std::swap(microSecondsSinceEpoch_, that.microSecondsSinceEpoch_);
  }

  // default copy/assignment/dtor are Okay
  string toString() const;
  string toFormattedString() const;
  bool valid() const { return microSecondsSinceEpoch_ > 0; }
  // for internal usage.
  int64_t microSecondsSinceEpoch() const { return microSecondsSinceEpoch_; }
  time_t secondsSinceEpoch() const
  { return static_cast<time_t>(microSecondsSinceEpoch_ / kMicroSecondsPerSecond); }
 //Get time of now.
  //获取当前时间
  static Timestamp now();
  //获取一个失效的时间，看第一个构造函数那里
  static Timestamp invalid();
 static const int kMicroSecondsPerSecond = 1000 * 1000;
 private:
  int64_t microSecondsSinceEpoch_;
};
//其他的号会自己实现
inline bool operator<(Timestamp lhs, Timestamp rhs)
{
  return lhs.microSecondsSinceEpoch() < rhs.microSecondsSinceEpoch();
}
inline bool operator==(Timestamp lhs, Timestamp rhs)
{
  return lhs.microSecondsSinceEpoch() == rhs.microSecondsSinceEpoch();
}
//Gets time difference of two timestamps, result in seconds.
//
// @param high, low
// @return (high-low) in seconds
// @c double has 52-bit precision, enough for one-microseciond
// resolution for next 100 years.
//用于计算两个时间的差
inline double timeDifference(Timestamp high, Timestamp low)
{
  int64_t diff = high.microSecondsSinceEpoch() - low.microSecondsSinceEpoch();//这里得到的是微秒
  return static_cast<double>(diff) / Timestamp::kMicroSecondsPerSecond;//转化为秒数
  //kMicroSecondsPerSecond为上面定义的一个常量
}
// Add @c seconds to given timestamp.
// @return timestamp+seconds as Timestamp
//在时间的基础上增加多少秒
inline Timestamp addTime(Timestamp timestamp, double seconds)
{
  int64_t delta = static_cast<int64_t>(seconds * Timestamp::kMicroSecondsPerSecond);//先把秒转化为微秒
  return Timestamp(timestamp.microSecondsSinceEpoch() + delta);//构造一个新的对象加上新的微秒
}

}
#endif  // MUDUO_BASE_TIMESTAMP_H

Timestamp.cc

//UTC 时间戳类实现文件
#include <muduo/base/Timestamp.h>

#include <sys/time.h>
#include <stdio.h>
#define __STDC_FORMAT_MACROS
#include <inttypes.h>//PRId64所在的头文件，在C++当中需要定义上面那个宏才可以使用PRId64
#undef __STDC_FORMAT_MACROS

#include <boost/static_assert.hpp>

using namespace muduo;
//编译时断言，在编译的时候检查 该条件是否满足
BOOST_STATIC_ASSERT(sizeof(Timestamp) == sizeof(int64_t));
//构造函数初始化赋值
Timestamp::Timestamp(int64_t microseconds): microSecondsSinceEpoch_(microseconds)
{
}

string Timestamp::toString() const
{
  char buf[32] = {0};
  int64_t seconds = microSecondsSinceEpoch_ / kMicroSecondsPerSecond;//得到秒数
  int64_t microseconds = microSecondsSinceEpoch_ % kMicroSecondsPerSecond;//得到微秒数
  //PRId64是为了实现跨平台，32位机器表示64位是lld，64位机器表示64位是ld
  snprintf(buf, sizeof(buf)-1, "%" PRId64 ".%06" PRId64 "", seconds, microseconds);
  return buf;
}
//把时间转化为一个格式化的字符串
string Timestamp::toFormattedString() const
{
  char buf[32] = {0};
  time_t seconds = static_cast<time_t>(microSecondsSinceEpoch_ / kMicroSecondsPerSecond);//得到距离1970年那个时间的秒数
  int microseconds = static_cast<int>(microSecondsSinceEpoch_ % kMicroSecondsPerSecond);//得到距离1970年那个时间的微秒数
  struct tm tm_time;
  gmtime_r(&seconds, &tm_time);//gmtime_r将一个秒数转化为结构体
//将时间结构体里面的时间取出来放进buf里面
  snprintf(buf, sizeof(buf), "%4d%02d%02d %02d:%02d:%02d.%06d", tm_time.tm_year + 1900, tm_time.tm_mon + 1, tm_time.tm_mday,
    tm_time.tm_hour, tm_time.tm_min, tm_time.tm_sec,microseconds);
  return buf;
}
//获取当前的时间
Timestamp Timestamp::now()
{
  struct timeval tv;
  gettimeofday(&tv, NULL);//这里返回一个timeval的结构体，第二个参数是一个时区，这里我们不需要返回
  int64_t seconds = tv.tv_sec;
  return Timestamp(seconds * kMicroSecondsPerSecond + tv.tv_usec);//得到的是距离19700101的微秒数的一个新的对象
}
//获取一个失效的时间
Timestamp Timestamp::invalid()
{
  return Timestamp();
}

测试文件在base/tests下面的Timestamp_unittest.cc
Timestamp_unittest.cc

//UTC 时间戳的测试代码
#include <muduo/base/Timestamp.h>
#include <vector>
#include <stdio.h>

using muduo::Timestamp;

void passByConstReference(const Timestamp& x)
{
  printf("%s
", x.toString().c_str());
}

void passByValue(Timestamp x)
{
  printf("%s
", x.toString().c_str());
}

void benchmark()
{//const常量前面加个K是谷歌推荐的编码规范
  const int kNumber = 1000*1000;

  std::vector<Timestamp> stamps;
  stamps.reserve(kNumber);//先预留kNumber个对象的空间
  for (int i = 0; i < kNumber; ++i)
  {//插入100w个now,目的是为了计算执行gettimeofday的时间
    stamps.push_back(Timestamp::now());
  }
  //c_str() 以 char* 形式传回 string 内含字符串
  printf("%s
", stamps.front().toString().c_str());//打印第一个插入的时间
  printf("%s
", stamps.back().toString().c_str());//打印最后一个插入的时间
  printf("%f
", timeDifference(stamps.back(), stamps.front()));//计算时间差

  int increments[100] = { 0 };
  int64_t start = stamps.front().microSecondsSinceEpoch();
  for (int i = 1; i < kNumber; ++i)
  {
    int64_t next = stamps[i].microSecondsSinceEpoch();
    int64_t inc = next - start;
    start = next;
    if (inc < 0)
    {
      printf("reverse!
");
    }
    else if (inc < 100)//时间差小于100
    {
      ++increments[inc];
    }
    else
    {
      printf("big gap %d
", static_cast<int>(inc));
    }
  }

  for (int i = 0; i < 100; ++i)
  {
    printf("%2d: %d
", i, increments[i]);
  }
}

int main()
{//构造一个时间戳对象，拷贝构造给now对象
  Timestamp now(Timestamp::now());
  printf("%s
", now.toString().c_str());//输出当前时间的toString,格式秒，微秒
  passByValue(now);
  passByConstReference(now);
  benchmark();//一个度量时间的函数
}

拿出来单独编译，运行可得到如下的结果：