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\n", x.toString().c_str());}void passByValue(Timestamp x){  printf("%s\n", 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\n", stamps.front().toString().c_str());//打印第一个插入的时间  printf("%s\n", stamps.back().toString().c_str());//打印最后一个插入的时间  printf("%f\n", 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!\n");    }    else if (inc < 100)//时间差小于100    {      ++increments[inc];    }    else    {      printf("big gap %d\n", static_cast<int>(inc));    }  }  for (int i = 0; i < 100; ++i)  {    printf("%2d: %d\n", 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\n", 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：