Question

The Time Profiler can measure the amount of time spent on certain methods. Is there a similar method that measures the number of times a method is called?

Answer 1

DTrace can do this, but only in the iPhone Simulator (it’s supported by Snow Leopard, but not yet by iOS). I have two writeups about this technology on MacResearch here and here where I walk through some case studies of using DTrace to look for specific methods and when they are called.

For example, I created the following DTrace script to measure the number of times methods were called on classes with the CP prefix, as well as total up the time spent in those methods:

#pragma D option quiet
#pragma D option aggsortrev

dtrace:::BEGIN
{
    printf("Sampling Core Plot methods ... Hit Ctrl-C to end.\n");
    starttime = timestamp;      
}

objc$target:CP*::entry
{
    starttimeformethod[probemod,probefunc] = timestamp;
    methodhasenteredatleastonce[probemod,probefunc] = 1;
}

objc$target:CP*::return
/methodhasenteredatleastonce[probemod,probefunc] == 1/
{
    this->executiontime = (timestamp - starttimeformethod[probemod,probefunc]) / 1000;
    @overallexecutions[probemod,probefunc] = count();
    @overallexecutiontime[probemod,probefunc] = sum(this->executiontime);
    @averageexecutiontime[probemod,probefunc] = avg(this->executiontime);
}

dtrace:::END 
{
    milliseconds = (timestamp - starttime) / 1000000;
    normalize(@overallexecutiontime, 1000);
    printf("Ran for %u ms\n", milliseconds);
    printf("%30s %30s %20s %20s %20s\n", "Class", "Method", "Total CPU time (ms)",  "Executions", "Average CPU time (us)");
    printa("%30s %30s %20@u %20@u %20@u\n", @overallexecutiontime, @overallexecutions, @averageexecutiontime);
}

This generates the following nicely formatted output:

        Class                         Method  Total CPU time (ms)           Executions Average CPU time (us)
      CPLayer                -drawInContext:                 6995                  352                19874
       CPPlot                -drawInContext:                 5312                   88                60374
CPScatterPlot      -renderAsVectorInContext:                 4332                   44                98455
CPXYPlotSpace        -viewPointForPlotPoint:                 3208                 4576                  701
       CPAxis               -layoutSublayers                 2050                   44                46595
CPXYPlotSpace -viewCoordinateForViewLength:linearPlotRange:plotCoordinateValue:                 1870                 9152
...

While you can create and run DTrace scripts from the command line, probably your best bet would be to create a custom instrument in Instruments and fill in the appropriate D code within that instrument. You can then easily run that against your application in the Simulator.

Again, this won’t work on the device, but if you just want statistics on the number of times something is called, and not the duration it runs for, this might do the job.