How do I accurately time how long it takes to call

问题:

I would like to know how long it's taking to send a message to an object with at least a 1ms accuracy. How do I do this?

回答1:

You can use mach_absolute_time to measure in nanoseconds.

#import <mach/mach_time.h>

uint64_t startTime = 0;
uint64_t endTime = 0;
uint64_t elapsedTime = 0;
uint64_t elapsedTimeNano = 0;

mach_timebase_info_data_t timeBaseInfo;
mach_timebase_info(&timeBaseInfo);

startTime = mach_absolute_time();

//do something here

endTime = mach_absolute_time();

elapsedTime = endTime - startTime;
elapsedTimeNano = elapsedTime * timeBaseInfo.numer / timeBaseInfo.denom;

Reference: Technical Q&A QA1398: Mach Absolute Time Units

回答2:

Here's what I do:

NSDate * start = [NSDate date];
// do whatever I need to time
NSLog(@"time took: %f", -[start timeIntervalSinceNow]);

The output will be in seconds (with a decimal portion). NSDates have resolution on the scale of milliseconds, although I'm not sure precisely how accurate they are.

If the code you're trying to time is too fast, put it in a loop that runs the code a hundred times. (That assumes, of course, that the code you're timing has no side effects.)

回答3:

Use dispatch_benchmark to log method execution time in nanoseconds.
It has a much nicer syntax than manually looping and calling mach_absolute_time() dispatch_benchmark is part of Grand Central Dispatch. This function is not publicly declared, so you’ll have to do that yourself before use :

extern uint64_t dispatch_benchmark(size_t count, void (^block)(void));

I am using this for log execution time :

size_t const  blockIterations = 1; //block call count
uint64_t t = dispatch_benchmark(blockIterations, ^{ //your code inside block
        [self TEST_processJSONDataRecordsWithCompletionHandler:^(id handler) {}];
    });
NSLog(@" Avg. Runtime in nanoseconds : %llu ns", t);

Credit goes to Benchmarking