setitimer函数使用笔记

setitimer函数使用笔记

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 */
            };

#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 ;
}