（10）muduo_base库源码分析：Timestamp.cc和Timestamp.h

1.Timestamp.h的研究

• Timestamp类图如下，参考下即可
  
• 位置：muduo\base\Timestamp.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_TIMESTAMP_H
#define MUDUO_BASE_TIMESTAMP_H

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

#include 


//
namespace muduo
{

///
/// Time stamp in UTC, in microseconds resolution.
///
/// This class is immutable.
/// It's recommended to pass it by value, since it's passed in register on x64.
///
/*
muduo:copyable表示空基类，标识类，值类型
值语义：可以拷贝的，拷贝之后，与原对象脱离关系
对象语义：要么是不能拷贝的，要么是可以拷贝的，拷贝之后与原对象仍然存在一定的关系，比如共享底层资源(要实现自己的拷贝构造函数)
muduo大部分都是对象语义
*/

class Timestamp : public muduo::copyable,
                  public boost::equality_comparable<Timestamp>,
                  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 microSecondsSinceEpochArg)
    : microSecondsSinceEpoch_(microSecondsSinceEpochArg)
  {
  }

  void swap(Timestamp& that)
  {
    //形参引用的改变能影响到实参，因为这里是引用
    std::swap(microSecondsSinceEpoch_, that.microSecondsSinceEpoch_);
  }

  // default copy/assignment/dtor are Okay

  string toString() const;
  string toFormattedString(bool showMicroseconds = true) 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.
  ///
  static Timestamp now();
  static Timestamp invalid()
  {
    return Timestamp();
  }

 
  static Timestamp fromUnixTime(time_t t)
  {
    return fromUnixTime(t, 0);
  }

  static Timestamp fromUnixTime(time_t t, int microseconds)
  {
    return Timestamp(static_cast<int64_t>(t) * kMicroSecondsPerSecond + microseconds);
  }

  static const int kMicroSecondsPerSecond = 1000 * 1000;

 private:
  int64_t microSecondsSinceEpoch_;
};

//equality_comparable和less_than_comparable的模板元的原因，要求实现<，可自动实现>,<=,>=

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-microsecond
/// resolution for next 100 years.
//1us=百万分之1s，两个微s相减/1000000，单位成为秒
inline double timeDifference(Timestamp high, Timestamp low)
{
  int64_t diff = high.microSecondsSinceEpoch() - low.microSecondsSinceEpoch();
  return static_cast<double>(diff) / Timestamp::kMicroSecondsPerSecond;
}

///
/// Add @c seconds to given timestamp.
///
/// @return timestamp+seconds as Timestamp
///
inline Timestamp addTime(Timestamp timestamp, double seconds)
{
  int64_t delta = static_cast<int64_t>(seconds * Timestamp::kMicroSecondsPerSecond);
  return Timestamp(timestamp.microSecondsSinceEpoch() + delta);
}

}  // namespace muduo

#endif  // MUDUO_BASE_TIMESTAMP_H

2.Timestamp.cc的研究

• 位置：muduo\base\Timestamp.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/Timestamp.h"

#include 
#include 

//用于宏PRId64能用
#ifndef __STDC_FORMAT_MACROS
#define __STDC_FORMAT_MACROS
#endif

#include 

using namespace muduo;

static_assert(sizeof(Timestamp) == sizeof(int64_t),
              "Timestamp is same size as int64_t");

string Timestamp::toString() const
{
  char buf[32] = {0};
  int64_t seconds = microSecondsSinceEpoch_ / kMicroSecondsPerSecond;
  int64_t microseconds = microSecondsSinceEpoch_ % kMicroSecondsPerSecond;

  /*
  int64_t用来表示64位整数，在32位系统中是long long int，在64位系统中是long int,所以打印int64_t的格式化方法是：
  printf(“%ld”, value);  // 64bit OS
  printf("%lld", value); // 32bit OS

  跨平台的做法：
  #define __STDC_FORMAT_MACROS
  #include 
  #undef __STDC_FORMAT_MACROS 
  printf("%" PRId64 "\n", value);  
  */
  //PRId64用于跨平台的，from：<inttypes.h>，若是64bit的，就等于ld，若是32bit的，就等于lld
  snprintf(buf, sizeof(buf)-1, "%" PRId64 ".%06" PRId64 "", seconds, microseconds);
  return buf;
}

string Timestamp::toFormattedString(bool showMicroseconds) const
{
  char buf[64] = {0};
  //求出距离1970.1.1的秒数
  time_t seconds = static_cast<time_t>(microSecondsSinceEpoch_ / kMicroSecondsPerSecond);
  struct tm tm_time;
  gmtime_r(&seconds, &tm_time);//_r表示线程，可以将秒数转换为tm_time结构体

  if (showMicroseconds)
  {
    int microseconds = static_cast<int>(microSecondsSinceEpoch_ % kMicroSecondsPerSecond);//转换成微妙数
    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);
  }
  else
  {
    snprintf(buf, sizeof(buf), "%4d%02d%02d %02d:%02d:%02d",
             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);
  }
  return buf;
}

//获取当前时间
Timestamp Timestamp::now()
{
  struct timeval tv;
  gettimeofday(&tv, NULL);//gettimeofday(,时区)，NULL表示没有时区
  int64_t seconds = tv.tv_sec;//表示tv.tv_sec秒
  return Timestamp(seconds * kMicroSecondsPerSecond + tv.tv_usec);//tv.tv_usec表示微妙
}

2.相关测试代码

• 目录结构
  （1）将muduo库下的build以及CMakeLists.txt拷贝至jmuduo目录下；
  （2）将muduo-master/muduo/base下的CMakeLists.txt，copyable.h，Timestamp.cc，Timestamp.h，Types.h拷贝到jmuduo/jmuduo/base下面；
  

修改后的内容如下：
===================================10\jmuduo\muduo\base\CMakeLists.txt=================================================
set(base_SRCS
  Timestamp.cc
  )##相当于：base_SRCS=Timestamp.cc

add_library(muduo_base ${base_SRCS}) ##将base_SRCS的文件生成为muduo_base的库
target_link_libraries(muduo_base pthread rt)##需要链接pthread库和rt库

install(TARGETS muduo_base DESTINATION lib)
file(GLOB HEADERS "*.h")
install(FILES ${HEADERS} DESTINATION include/muduo/base)

if(NOT CMAKE_BUILD_NO_EXAMPLES)
  add_subdirectory(tests)
endif()

• 测试BOOST_STATIC_ASSERT运行时的断言相关代码，assert是运行时的断言
  （1）在jmuduo/tests/下添加：bsa.cc以及CMakeLists.txt文件；
  （2）此外还需要在jmuduo/CMakeLists.txt下添加：add_subdirectory(tests)；
  （3）直接在jmuduo下面，运行./build即可

===========================================10\jmuduo\tests\bsa.cc=======================================================
#include 

class Timestamp
{
private:
	int64_t microSecondsSinceEpoch_;
};

//编译时的断言，来自boost库，assert是运行时的断言
BOOST_STATIC_ASSERT(sizeof(Timestamp) == sizeof(int64_t));//在编译的时候不会出错
//BOOST_STATIC_ASSERT(sizeof(int) == sizeof(short));//在编译的时候会出错

int main(void)
{
	return 0;
}

======================================10\jmuduo\tests\CMakeLists.txt===============================================
add_executable(bsa bsa.cc)


========================================10\jmuduo\CMakeLists.txt=================================================

。。。。。
，，，，，
。。。。
add_subdirectory(tests)##这里是为了编译tests文件夹下的bsa.cc和Cmake文件

• 测试imestamp_unittest.cc。来自muduo\base\tests\Timestamp_unittest.cc
  （1）将muduo的Timestamp_unittest.cc拷贝至10\jmuduo\muduo\base\tests\Timestamp_unittest.cc
  （2）在10\jmuduo\muduo\base\tests\目录下添加：CMakeLists.txt
  （3）在10\jmuduo\下，执行build.sh

==================================10\jmuduo\muduo\base\tests\CMakeLists.txt===================
add_executable(timestamp_unittest Timestamp_unittest.cc)##可执行文件是：timestamp_unittest
target_link_libraries(timestamp_unittest muduo_base)##需要链接muduo_base库

================================10\jmuduo\muduo\base\tests\Timestamp_unittest.cc代码解释如下：=======================
#include "muduo/base/Timestamp.h"
#include 
#include 

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 int kNumber = 1000*1000;//const常量加个k，这是google的编码规范

  std::vector<Timestamp> stamps;
  stamps.reserve(kNumber);//预留了能容纳100万个Timestamp的空间
  for (int i = 0; i < kNumber; ++i)
  {
    //插入100万个时间
    stamps.push_back(Timestamp::now());//这里消耗的时间主要是now函数的gettimeofday,push_bak已经预留了空间，所以不会消耗时间
  }
  printf("%s\n", stamps.front().toString().c_str());
  printf("%s\n", stamps.back().toString().c_str());
  printf("%f\n", timeDifference(stamps.back(), stamps.front()));//计算最后一个时间和第一个时间的时间差

  int increments[100] = { 0 };
  int64_t start = stamps.front().microSecondsSinceEpoch();//相当于下标为0的时间
  for (int i = 1; i < kNumber; ++i)
  {
    int64_t next = stamps[i].microSecondsSinceEpoch();
    int64_t inc = next - start;//时间差
    start = next;
    if (inc < 0)
    {
      printf("reverse!\n");
    }
    else if (inc < 100)
    {
      ++increments[inc];//小于100的个数++
    }
    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()
{
  //调用拷贝构造函数：用一个对象初始化另一个对象
  //Timestamp::now()是没有名称的对象，所以将其构造函数的值拷贝给now对象，看now里面的return代码就明白了！！
  Timestamp now(Timestamp::now());//等价于：Timestamp now=Timestamp::now()
  printf("%s\n", now.toString().c_str());
  passByValue(now);//值传递
  passByConstReference(now);//引用传递
  benchmark();//这是个基准函数
}

• 结果展示：

代码位置：可以参考下，
wangji/src/10/build/debug/bin$ ./timestamp_unittest

• 其它文件：10\jmuduo\build.sh，10\jmuduo\CMakeLists.txt

===================================10\jmuduo\build.sh==========================
#!/bin/sh

set -x

SOURCE_DIR=`pwd`
BUILD_DIR=${BUILD_DIR:-../build}
BUILD_TYPE=${BUILD_TYPE:-debug}
INSTALL_DIR=${INSTALL_DIR:-../${BUILD_TYPE}-install}
BUILD_NO_EXAMPLES=${BUILD_NO_EXAMPLES:-0}

mkdir -p $BUILD_DIR/$BUILD_TYPE \
  && cd $BUILD_DIR/$BUILD_TYPE \
  && cmake --graphviz=dep.dot \
           -DCMAKE_BUILD_TYPE=$BUILD_TYPE \
           -DCMAKE_INSTALL_PREFIX=$INSTALL_DIR \
           -DCMAKE_BUILD_NO_EXAMPLES=$BUILD_NO_EXAMPLES \
           $SOURCE_DIR \
  && make $*

cd $SOURCE_DIR && doxygen


==================================10\jmuduo\CMakeLists.txt==================================
cmake_minimum_required(VERSION 2.6)

project(muduo CXX)

if(NOT CMAKE_BUILD_TYPE)
  set(CMAKE_BUILD_TYPE "Debug")
endif()

set(CXX_FLAGS
 -g
 # -DVALGRIND
 # -DMUDUO_STD_STRING
 -D_FILE_OFFSET_BITS=64
 -Wall
 -Wextra
 -Werror
 -Wconversion
 -Wno-unused-parameter
 -Wold-style-cast
 -Woverloaded-virtual
 -Wpointer-arith
 -Wshadow
 -Wwrite-strings
 -march=native
 # -MMD
 # -std=c++0x
 -rdynamic
 )
if(CMAKE_BUILD_BITS EQUAL 32)
  list(APPEND CXX_FLAGS "-m32")
endif()
string(REPLACE ";" " " CMAKE_CXX_FLAGS "${CXX_FLAGS}")

set(CMAKE_CXX_COMPILER "g++")
#set(CMAKE_CXX_COMPILER "icpc")
set(CMAKE_CXX_FLAGS_DEBUG "-O0")
set(CMAKE_CXX_FLAGS_RELEASE "-O2 -finline-limit=1000 -DNDEBUG")
set(EXECUTABLE_OUTPUT_PATH ${PROJECT_BINARY_DIR}/bin)
set(LIBRARY_OUTPUT_PATH ${PROJECT_BINARY_DIR}/lib)

find_package(Boost REQUIRED)
find_package(Protobuf)
find_package(CURL)
find_path(CARES_INCLUDE_DIR ares.h)
find_library(CARES_LIBRARY NAMES cares)
find_path(MHD_INCLUDE_DIR microhttpd.h)
find_library(MHD_LIBRARY NAMES microhttpd)
find_library(BOOSTTEST_LIBRARY NAMES boost_unit_test_framework)

include_directories(${Boost_INCLUDE_DIRS})

include_directories(${PROJECT_SOURCE_DIR})

string(TOUPPER ${CMAKE_BUILD_TYPE} BUILD_TYPE)
message(STATUS "CXX_FLAGS = " ${CMAKE_CXX_FLAGS} " " ${CMAKE_CXX_FLAGS_${BUILD_TYPE}})

add_subdirectory(muduo/base) ##添加编译子目录
#add_subdirectory(muduo/net)

###下面是muduo的examples，目前还没，所以注释了
#if(NOT CMAKE_BUILD_NO_EXAMPLES)
#  add_subdirectory(examples)
#else()
#  if(CARES_INCLUDE_DIR AND CARES_LIBRARY)
#    add_subdirectory(examples/cdns)
#  endif()
#endif()

add_subdirectory(tests)##这里是为了编译tests文件夹下的bsa.cc和Cmake文件