// timebase_demo.c
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <mach/mach.h>
#include <mach/mach_time.h>
#define DEFAULT_SLEEP_TIME 1
#define MAXIMUM_SLEEP_TIME 60
int
main(int argc, char **argv)
{
kern_return_t kr;
u_int64_t t1, t2, diff;
double abs2clock;
int sleeptime = DEFAULT_SLEEP_TIME;
mach_timebase_info_data_t info;
kr = mach_timebase_info(&info);
if (kr != KERN_SUCCESS) {
mach_error("mach_timebase_info:", kr);
exit(kr);
}
if (argc == 2) {
sleeptime = atoi(argv[1]);
if ((sleeptime < 0) || (sleeptime > MAXIMUM_SLEEP_TIME))
sleeptime = DEFAULT_SLEEP_TIME;
}
t1 = mach_absolute_time();
sleep(sleeptime);
t2 = mach_absolute_time();
diff = t2 - t1;
printf("slept for %d seconds of clock time\n", sleeptime);
printf("TB increments = %llu increments\n", diff);
printf("absolute-to-clock conversion factor = (%u/%u) ns/increment\n",
info.numer, info.denom);
printf("sleeping time according to TB\n");
abs2clock = (double)info.numer/(double)info.denom;
abs2clock *= (double)diff;
printf("\t= %llu increments x (%u/%u) ns/increment\n\t= %f ns\n\t= %f s\n",
diff, info.numer, info.denom,
abs2clock, abs2clock/(double)1000000000);
exit(0);
}
haidragondeMacBook-Pro:7-41 haidragon$ gcc -Wall -o timebase_demo timebase_demo.c
haidragondeMacBook-Pro:7-41 haidragon$ ls
timebase_demo timebase_demo.c
haidragondeMacBook-Pro:7-41 haidragon$ ./timebase_demo
slept for 1 seconds of clock time
TB increments = 1002722462 increments
absolute-to-clock conversion factor = (1/1) ns/increment
sleeping time according to TB
= 1002722462 increments x (1/1) ns/increment
= 1002722462.000000 ns
= 1.002722 s
haidragondeMacBook-Pro:7-41 haidragon$ ./timebase_demo 5
slept for 5 seconds of clock time
TB increments = 5003092227 increments
absolute-to-clock conversion factor = (1/1) ns/increment
sleeping time according to TB
= 5003092227 increments x (1/1) ns/increment
= 5003092227.000000 ns
= 5.003092 s
haidragondeMacBook-Pro:7-41 haidragon$ 原文地址：https://blog.51cto.com/haidragon/2417841