mach_absolute_time

#import <mach/mach_time.h>
//获取Mach时间
uint64_t _startTime = mach_absolute_time();
uint64_t endTime = mach_absolute_time();
NSLog(@"%f", substractTime(endTime, _startTime));

//获取系统的时间基准
double substractTime(uint64_t endTime, uint64_t startTime) {
    uint64_t difference = endTime - startTime;
    static double conversion = 0.0;
    if (conversion == 0.0) {
        mach_timebase_info_data_t info;
        //mach_timebase_info() 获取时间基准info结构体
        kern_return_t err = mach_timebase_info(&info);
        if (err == 0 ) {
            //用结构体中的分子项/分母项 即为时间基准
            //乘以1e-9获取秒级别(1e-9即为1纳秒)
            conversion= 1e-9 * (double) info.numer / (double) info.denom;
        }
    }
    return conversion * (double)difference;;
    
}