Acquisition of precise time in iOS

Here is an impossible to verify the source of English and their own translation

A quick and easy-to-measure the performance of a piece of IOS code is to dig down below all the Cocoa Touch stuff and Use the low-level mach_absolute_time . This call returns a ticks count that can is converted into nanoseconds using information obtained from the call mach_timebase_info . The following code sketches out the technique:

An easy and quick way to accurately measure the performance of an iOS code is to dig deep into the layers below the cocoa touch layer-using the underlying call Mach_absolute_time. The Mach_absolute_time returns the tick count counter of the CPU (which is considered a CPU time privately), and the returned time can be converted to a nanosecond level. The following is a demonstration of the implementation of the underlying call mach_absolute_time.

Add (Attached)

#import <mach/mach_time.h>//Import the underlying framework to invoke

Double Machtimetosecs (uint64_t time)//cpu TickCount conversion into a function

{

mach_timebase_info_data_t timebase;

Mach_timebase_info(&timebase);

return (Double) time * (Double) timebase. Numer/

(double) timebase. denom/1e9;

}

-(void) profiledosomething// method of detecting code execution time

{

uint64_t begin = Mach_absolute_time(); Get time with Mach_absolute_time()

Here's the iOS code to test,

For (int i = 0; i <; i++) {

NSLog (@ "Test");

}

uint64_t end = Mach_absolute_time(); Get time with Mach_absolute_time()

NSLog(@ "Time taken to dosomething%g S",

machtimetosecs (End-begin)); End-begin and then convert, you get the exact execution time.

}

The timebase values on the simulator, in least on my MacBook Air, is 1/1, however on the IPad and IPhone 4 they is 125/3 ; So don ' t is lazy and hard code them.

(This paragraph in English mainly talk about different test equipment to get different results, because the landlord do not know 1/1,125/3 what meaning so this paragraph is not translated)

Never assume that because something runs quickly on the simulator it would also run quickly on a target device. On II jobs last year I encountered code this took 100x longer to run a iPad than in the simulator.

Never assume that the code performs as efficiently on the emulator as it does on the target device (such as the iphone 5). I met a piece of code last year that ran 100X more on the ipad than on the simulator.

Acquisition of precise time in iOS