linux中setitimer函数用法

linux中setitimer函数用法

（一） 函数原型：

int setitimer(int which, const struct itimerval *value,

struct itimerval *ovalue);

DESCRIPTION

The system provides each process with three interval timers, each decrementing in a distinct time domain. When any timer expires, a

signal is sent to the process, and the timer (potentially) restarts.

ITIMER_REAL decrements in real time, and delivers SIGALRM upon expiration.

ITIMER_VIRTUAL decrements only when the process is executing, and delivers SIGVTALRM upon expiration.

ITIMER_PROF decrements both when the process executes and when the system is executing on behalf of the process. Coupled with

ITIMER_VIRTUAL, this timer is usually used to profile the time spent by the application in user and kernel space. SIG-

PROF is delivered upon expiration.

Timer values are defined by the following structures:

struct itimerval {

struct timeval it_interval; /* next value */

struct timeval it_value; /* current value */

};

struct timeval {

long tv_sec; /* seconds */

long tv_usec; /* microseconds */

};



参数：

which：间歇计时器类型，有三种选择

ITIMER_REAL //数值为0，计时器的值实时递减，发送的信号是SIGALRM。

ITIMER_VIRTUAL //数值为1，进程执行时递减计时器的值，发送的信号是SIGVTALRM。

ITIMER_PROF //数值为2，进程和系统执行时都递减计时器的值，发送的信号是SIGPROF。

value，ovalue：时间参数，原型如下

struct itimerval {

struct timeval it_interval; /* 计时器重启动的间歇值 */

struct timeval it_value; /* 计时器安装后首先启动的初始值 */

};

struct timeval {

long tv_sec; /* 秒 */

long tv_usec; /* 微妙(1/1000000) */

};

getitimer()用计时器的当前值填写value指向的结构体。

setitimer()将value指向的结构体设为计时器的当前值，如果ovalue不是NULL，将返回计时器原有值。

返回说明：

成功执行时，返回0。失败返回-1，errno被设为以下的某个值

EFAULT：value或ovalue是不有效的指针

EINVAL：其值不是ITIMER_REAL，ITIMER_VIRTUAL 或 ITIMER_PROF之一

（二）setitimer用法示例：

#include <stdio.h>

#include <unistd.h>

#include <signal.h>

#include <string.h>

#include <sys/time.h>

#include <errno.h>

void PrintMsg(int Num)

{

printf("%s\n", "Hello World");

return;

}

int main(int argc, char* argv[])

{

signal(SIGALRM, PrintMsg);

struct itimerval tick;

tick.it_value.tv_sec = 10; //十秒钟后将启动定时器

tick.it_value.tv_usec = 0;

tick.it_interval.tv_sec =1; //定时器启动后，每隔1秒将执行相应的函数

tick.it_interval.tv_usec = 0;

//setitimer将触发SIGALRM信号

int ret = setitimer(ITIMER_REAL, &tick, NULL);

if ( ret != 0)

{

printf("Set timer error. %s \n", strerror(errno) );

return -1;

}

printf("Wait!\n");

getchar();

return 0;

}