Measure time between library call and callback

问题

Hi: In an iPhone application I use a library(C++) which asynchronously makes a callback when computation is finished. Now I want to measure the time which is spent -including the method which calls the library- until the callback is made. Are there any possibilities to do this with the Instruments application from Apple? What are the best practices?

回答1:

In the past I have used the following for making network calls I had to optimize - although at first it seems a bit convoluted, it certainly gives the most accurate times I have seen.

uint64_t time_a = mach_absolute_time();

// do stuff

uint64_t time_b = mach_absolute_time();

[self logTime:(time_b-time_a)];

- (void) logTime:(uint64_t)machTime {
    static double timeScaleSeconds = 0.0;
    if (timeScaleSeconds == 0.0) {
        mach_timebase_info_data_t timebaseInfo;
        if (mach_timebase_info(&timebaseInfo) == KERN_SUCCESS) {
            double timeScaleMicroSeconds = ((double) timebaseInfo.numer / (double) timebaseInfo.denom) / 1000;
            timeScaleSeconds = timeScaleMicroSeconds / 1000000;
        }
    }

    NSLog(@"%g seconds", timeScaleSeconds*machTime);
}

回答2:

I have written a c++ class to wrap the mach_absolute_time calls. This makes it handy to sprinkle in the code at the start/stop of events for measuring time difference.

It also works well if you want to use it in a class to do timing (between calls) or for state based behavior (do something after the timer reaches X).

StopWatch.h

class StopWatch
{
private:
        uint64 _start;
        uint64 _stop;
        uint64 _elapsed;
public:
   void Start();
   void Stop();
   void Reset();
   void Continue();
   double GetSeconds();
};

StopWatch.cpp

#include "Stopwatch.h"
#include <mach/mach_time.h>


void StopWatch::Start()
{
        _stop = 0;
        _elapsed = 0;
        _start = mach_absolute_time();
}

void StopWatch::Stop()
{
        _stop = mach_absolute_time();
   if(_start > 0)
   {
      if(_stop > _start)
      {
         _elapsed = _stop - _start;
      }
   }
}

void StopWatch::Reset()
{
   _start = 0;
   _stop  = 0;
   _elapsed = 0;
}

void StopWatch::Continue()
{
   _elapsed = 0;
   _stop = 0;
}

double StopWatch::GetSeconds()
{
   double elapsedSeconds = 0.0;
   uint64 elapsedTimeNano = 0;

        if(_elapsed > 0)
        {  // Stopped
                mach_timebase_info_data_t timeBaseInfo;
                mach_timebase_info(&timeBaseInfo);
                elapsedTimeNano = _elapsed * timeBaseInfo.numer / timeBaseInfo.denom;
                elapsedSeconds = elapsedTimeNano * 1.0E-9;
        }
        else if(_start > 0)
        {  // Running or Continued
      uint64_t elapsedTemp;
                uint64_t stopTemp = mach_absolute_time();
      if(stopTemp > _start)
      {
         elapsedTemp = stopTemp - _start;
      }
      else
      {
         elapsedTemp = 0;
      }
                mach_timebase_info_data_t timeBaseInfo;
                mach_timebase_info(&timeBaseInfo);
                elapsedTimeNano = elapsedTemp * timeBaseInfo.numer / timeBaseInfo.denom;
                elapsedSeconds = elapsedTimeNano * 1.0E-9;
        }
   return elapsedSeconds;
}

来源：https://stackoverflow.com/questions/2673966/measure-time-between-library-call-and-callback

标签

c++

iphone

objective-c

instruments

performance