解读Time类

• 头文件：nstime.h
• 源文件：time.cc
  这是一个带单位的ns3中的表示时间的类，以定义了+-*/ << >>操作符。

创建时间

都是类的函数

Time From (const int64x64_t & value);Time FromInteger (uint64_t value, enum Unit unit);Time From (const int64x64_t & value, enum Unit unit)；Time FromDouble (double value, enum Unit unit)；inline Time Years (double value)；inline Time Days (double value)；inline Time Hours (double value)；inline Time Minutes (double value)；inline Time Seconds (double value)；inline Time MilliSeconds (uint64_t value)；inline Time MicroSeconds (uint64_t value)；inline Time NanoSeconds (uint64_t value)；inline Time PicoSeconds (uint64_t value)；inline Time FemtoSeconds (uint64_t value)；

使用示例

Time t = Seconds (2.0);Simulator::Schedule (Seconds (5.0), ...);

时间转换

Get**

如GetYears，GetDays等。返回值为double,通过调用ToDouble(单位)实现

To**

inline int64_t ToInteger (enum Unit unit) const；inline double ToDouble (enum Unit unit) const；

time对象的输入输出

Time:: As

TimeWithUnit As (const enum Unit unit) const;
生成一个TimeWithUnit对象。重定义输出操作符时通过调用该函数实现

<<

调用TimeWithUnit的输出（也就是输出是带单位的）

>>

调用explicit Time (const std::string & s)(只接受类似”1ms”的形式)

数据结构

enum Unit  {    Y   = 0,   //!< year, 365 days    D   = 1,   //!< day, 24 hours    H   = 2,   //!< hour, 60 minutes    MIN = 3,   //!< minute, 60 seconds    S   = 4,   //!< second    MS  = 5,   //!< millisecond    US  = 6,   //!< microsecond    NS  = 7,   //!< nanosecond    PS  = 8,   //!< picosecond    FS  = 9,   //!< femtosecond    LAST = 10  };struct Information  {    bool toMul;                     //!< Multiply when converting To, otherwise divide    bool fromMul;                   //!< Multiple when converting From, otherwise divide    int64_t factor;                 //!< 此单位和当前单位的比率因子。两者之间的较大者比上较小者的比值。    int64x64_t timeTo;              //!< Multiplier to convert to this unit    int64x64_t timeFrom;            //!< Multiplier to convert from this unit  };  /** Current time unit, and conversion info. */  struct Resolution  {    struct Information info[LAST];  //!<  Conversion info from current unit    enum Time::Unit unit;           //!<  Current time unit  };

类型重定义

typedef std::set< Time * > MarkedTimes;

重要成员变量

static MarkedTimes * g_markingTimes;//记录所有time类的实例 int64_t m_data;  //!< Virtual time value, in the current unit.

构造函数

• 复制控制
  传入参数类型有：Time&，以及赋值操作符=
• 形参为基本数据类型的构造函数
  int，long int等各种基本数据类型，用于初始化m_data;

- explicit Time (const std::string & s)(只接受类似”1ms”的形式)

析构函数

 ~Time (){    if (g_markingTimes)        Clear (this); }

初始化

• 静态成员g_markingTimes初始化为0
• GetMarkingMutex()

SystemMutex &GetMarkingMutex (){  static SystemMutex g_markingMutex;  return g_markingMutex;}

• Time::StaticInit ()

bool Time::StaticInit (){  static bool firstTime = true;  CriticalSection critical (GetMarkingMutex ());  if(firsttime && !g_markingTimes){  static MarkedTimes markingTimes;  g_markingTimes = & markingTimes;  }  else  NS_LOG_ERROR ();  return (firstTime = false);  }

重要函数

Time::Mark (Time * const time)

根据g_markingMutex创建临界区，在临界区去中将time指向的时间插入g_markingTimes中。

Time::Clear (Time * const time)

根据g_markingMutex创建临界区，在临界区去中从g_markingTimes中删除time

Time:: ConvertTimes

static void ConvertTimes (const enum Unit unit);
创建临界访问区，将g_markingTimes中的所有时间改成目标单位下的值

分辨率相关函数

SetResolution

设置分辨率也就是设置当前使用的时间单位，以及其它单位与该单位相互转换时需要参考的转换信息。（设置Resolution:: info[LAST];)

void Time::SetResolution (enum Unit unit, struct Resolution *resolution, const bool convert /* = true */){if (convert)  ConvertTimes (unit);for (int i = 0; i < Time::LAST; i++)    {    struct Information *info = &resolution->info[i];    info->factor = factor;    if (shift == 0 && quotient == 1)    //info[i]为基准单位到自身的转换参考信息        {          info->timeFrom = int64x64_t (1);          info->timeTo = int64x64_t (1);          info->toMul = true;          info->fromMul = true;        }      else if (realFactor > 1)      //info[i]为比基准单位大的单位与基准单位相互转换的参考信息        {          info->timeFrom = int64x64_t (factor);          info->timeTo = int64x64_t::Invert (factor);          info->toMul = false;          info->fromMul = true;//该单位比基准单位大，因此从此单位转换到基准单位时应该要乘以info->timeFrom。此种情况下factor=realFactor。        }      else        {          NS_ASSERT (realFactor < 1);          info->timeFrom = int64x64_t::Invert (factor);          info->timeTo = int64x64_t (factor);          info->toMul = true;//该单位比基准单位小，因此从基准单位转换到该单位时应该要乘以info->timeto。此种情况下factor=realFactor。          info->fromMul = false;        }}

SetDefaultNsResolution

struct Resolution resolution;SetResolution (Time::NS, &resolution, false);return resolution;static struct Resolution SetDefaultNsResolution (void)

PeekResolution

static inline struct Resolution *PeekResolution (void)  {    static struct Time::Resolution resolution = SetDefaultNsResolution ();//只有该函数被第一次执行的时候才会执行这个句子。实现单例。    return & resolution;  }

SetResolution

voidTime::SetResolution (enum Unit resolution){  NS_LOG_FUNCTION (resolution);  SetResolution (resolution, PeekResolution ());}

inline double ToDouble (enum Unit unit) const  {    return To (unit).GetDouble ();//调用To函数得到一个int64x64_t对象，然后调用该对对象的方法的方法得到一个Double数。  }  inline int64x64_t To (enum Unit unit) const  {    struct Information *info = PeekInformation (unit);    int64x64_t retval = int64x64_t (m_data);    if (info->toMul)        retval *= info->timeTo;    else        retval.MulByInvert (info->timeTo);    return retval;  }

相关函数调用链

ToDouble->To->PeekResolution->SetDefaultNsResolution (void)

读不懂的地方

强制调用初始化函数

宏定义在used.h文件中
static bool NS_UNUSED_GLOBAL (g_TimeStaticInit) = Time::StaticInit ();

Abs

friend Time Abs (const Time & time)
为什么 time.m_data会出现小于零的情况呢？

TimeStep

这个函数的具体作用会是什么呢
inline Time TimeStep (uint64_t ts)
{
return Time (ts);
}

NS_UNUSED_GLOBAL宏

-这个宏和括号中的变量是什么时候定义的

/// Force static initialization of Time,StaticInit函数返回布尔值，所以我猜这个地方是定义一个g_TimeStaticInit全局变量，并让其等于函数返回值static bool NS_UNUSED_GLOBAL (g_TimeStaticInit) = Time::StaticInit ();

测试demo

#include "ns3/nstime.h"#include "iostream"using namespace ns3;using namespace std;int main(){    Time t3;    cin >> t3;//输入支持数值＋单位的形式，如1h,2min.支持的单位如下　　/**- `s`  (seconds)   * - `ms` (milliseconds)   * - `us` (microseconds)   * - `ns` (nanoseconds)   * - `ps` (picoseconds)   * - `fs` (femtoseconds)   * - `min`  (minutes)   * - `h`  (hours)   * - `d`  (days)   * - `y`  (years)*/    cout << "t3 is:" << t3.As(Time::MIN)<< endl;    t3  = Minutes(3);//令t3值为３分钟    cout << "new value of t3:"<< t3 << endl;    Time t4 = Seconds(60);//令t3值为60s.    /*此外常见的创建时间的函数有Years (double value)；Days (double value)；Hours (double value)；Minutes (double value)；Seconds (double value)；*/    cout << t4 << endl;    cout << (t3/t4) << endl;//此处得到的结果为３，合乎逻辑    return 0;}