mac os x使用Mach调用设置时间警报(回调)

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <mach/mach.h>
#include <mach/clock.h>

#define OUT_ON_MACH_ERROR(msg, retval) if (kr != KERN_SUCCESS) { mach_error(msg ":" , kr); goto out; }

// Structure for the IPC message we will receive from the clock
typedef struct msg_format_recv_s {
mach_msg_header_t header;
int data;
mach_msg_trailer_t trailer;
} msg_format_recv_t;

int
main()
{
kern_return_t kr;
clock_serv_t clk_system;
mach_timespec_t alarm_time;
clock_reply_t alarm_port;
struct timeval t1, t2;
msg_format_recv_t message;
mach_port_t mytask;

// The C library optimized this call by returning the task port‘s value
// that it caches in the mach_task_self_ variable
mytask = mach_task_self();

kr = host_get_clock_service(mach_host_self(), SYSTEM_CLOCK,
(clock_serv_t *)&clk_system);
OUT_ON_MACH_ERROR("host_get_clock_service", kr);

// Let us set the alarm to ring after 2.5 seconds
alarm_time.tv_sec = 2;
alarm_time.tv_nsec = 500;

// Allocate a port (specifically, get receive right for the new port)
// We will use this port to receive the alarm message from the clock
kr = mach_port_allocate(
mytask, // the task acquiring the port right
MACH_PORT_RIGHT_RECEIVE, // type of right
&alarm_port); // task‘s name for the port right
OUT_ON_MACH_ERROR("mach_port_allocate", kr);

gettimeofday(&t1, NULL);

// Set the alarm
kr = clock_alarm(clk_system, // the clock to use
TIME_RELATIVE, // how to interpret alarm time
alarm_time, // the alarm time
alarm_port); // this port will receive the alarm message
OUT_ON_MACH_ERROR("clock_alarm", kr);

printf("Current time %ld s + %d us\n"
"Setting alarm to ring after %d s + %d ns\n",
t1.tv_sec, t1.tv_usec, alarm_time.tv_sec, alarm_time.tv_nsec);

// Wait to receive the alarm message (we will block here)
kr = mach_msg(&(message.header), // the message buffer
MACH_RCV_MSG, // message option bits
0, // send size (we are receiving, so 0)
message.header.msgh_size,// receive limit
alarm_port, // receive right
MACH_MSG_TIMEOUT_NONE, // no timeout
MACH_PORT_NULL); // no timeout notification port
// We should have received an alarm message at this point
gettimeofday(&t2, NULL);
OUT_ON_MACH_ERROR("mach_msg", kr);

if (t2.tv_usec < t1.tv_usec) {
t1.tv_sec += 1;
t1.tv_usec -= 1000000;
}

printf("\nCurrent time %ld s + %d us\n", t2.tv_sec, t2.tv_usec);
printf("Alarm rang after %ld s + %d us\n", (t2.tv_sec - t1.tv_sec),
(t2.tv_usec - t1.tv_usec));

out:
mach_port_deallocate(mytask, clk_system);

// Release user reference for the receive right we created
mach_port_deallocate(mytask, alarm_port);