1、纳秒级精度的Timer
#include <mach/mach.h>
#include <mach/mach_time.h>
static const uint64_t NANOS_PER_USEC = 1000ULL;
static const uint64_t NANOS_PER_MILLISEC = 1000ULL * NANOS_PER_USEC;
static const uint64_t NANOS_PER_SEC = 1000ULL * NANOS_PER_MILLISEC;
static mach_timebase_info_data_t timebase_info;
static uint64_t abs_to_nanos(uint64_t abs) {
return abs * timebase_info.numer / timebase_info.denom;
}
static uint64_t nanos_to_abs(uint64_t nanos) {
return nanos * timebase_info.denom / timebase_info.numer;
}
void example_mach_wait_until(int argc, const char * argv[]) {
mach_timebase_info(&timebase_info);
uint64_t time_to_wait = nanos_to_abs(10ULL * NANOS_PER_SEC);
uint64_t now = mach_absolute_time();
mach_wait_until(now + time_to_wait);
}
2、后台开一个常驻线程，无繁重任务，开启一个NSTimer。
