Linux system programming-setitimer functions

Function: In Linux system programming, Setitimer is a function that is used frequently to realize the function of delay and timing.

Header file: sys/time.h

Function Prototypes:

int setitimer (int  which,              conststruct itimerval *New_value,               struct itimerval *old_value);

Parameter meaning:

1, the which parameter is used to set the timer type, the optional value is

(1) Itimer_real: Set the timer to time the system is real, and send SIGALRM signal after running the specified time.

(2) Itimer_virtual: When the setup process executes in user space, the time count is reduced. Send SIGVTALRM signal after running a specified time

(3) Itimer_prof: When the setup process executes in kernel space, the time count is reduced. Sends a SIGPROF signal after the specified time has elapsed.

2, New_value parameters: used to set the timer timing time

3, Old_value parameters: Rarely used, often set to null. It is used to store the New_value value that was set when the last Setitimer call was made.

Itimerval Structural Body:

 struct   timeval{time_t tv_sec;  /*   s       */  suseconds_t tv_usec;  /*   microseconds (10^ ( -6))  */ };  struct   itimerval{ struct  timeval it_interval; /*   time to generate the timer signal again     */    struct  timeval it_value; /*   The first time a timer signal is generated  */ };  

SetTimer mechanism: First it_value in the which parameter setting countdown, when the It_value is zero will send a signal. The it_value is then reset to the value of It_interval. Finally restart the new round of timing, in this way the cycle continues.

Attention:

1, the value of It_value is 0, will not send a signal. So to be able to send a signal, It_value is worth more than 0.

2, the value of It_interval is 0, the timer will only send a signal, that is, only delay, can not be timed.

Demo Program:

1#include <stdio.h>2#include <sys/time.h>3#include <unistd.h>4#include <stdlib.h>5#include <string.h>6#include <signal.h>7 8 voidCall_back (intSig)9 {Ten     Static intCount =1; Oneprintf"call_back:%d\n", count++); A } -  - intMainvoid) the { - signal (SIGALRM, call_back); -     structitimerval New_value; -memset (&new_value,0,sizeof(New_value)); +  -New_value.it_interval.tv_sec =1;//Set the timer time to 1S +New_value.it_interval.tv_usec =0; ANew_value.it_value.tv_sec =2;//set the first timer time to 2S atNew_value.it_value.tv_usec =0; -  -     intret = Setitimer (itimer_real, &New_value, NULL); -     if(0!=ret) -     { -Perror ("Setitimer"); inExit (-1); -     } to GetChar (); +  -     return 0; the}

Operation Result:

Linux system programming-setitimer functions