Using Timers in Linux

1. Call the alarm function using Signal SIGALRM No. 14th

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include < Signal.h>void handle (int signum) {printf ("hello\n");} int main (int argc, const char *argv[]) {    signal (SIGALRM, handle);    while (1)    {        alarm (3);        Sleep (3);    }    return 0;}

Sends a SIGALRM signal to itself every 3 seconds, signal calls handle for processing after receiving SIGALRM signal

--"alarm can only be accurate to seconds.

2.setitimer is also processed by sending a signal to itself, but can be accurate to the ACME level

int Setitimer (int which, const struct Itimerval *new_value,
struct Itimerval *old_value);

Itimer_real decrements in REAL time, and delivers sigalrm upon expiration.

Itimer_virtual decrements only if the process is executing, and delivers
SIGVTALRM upon expiration.

itimer_prof    decrements Both when the process executes and then the system is
   &N bsp;                  executing  on  behalf  of the process.  coupled with itimer_vir-
                       tual, this timer is usually used to profiles the  time  spent  by
                       the  application in user and Kernel space.  sigprof is delivered
                       upon expiration.

struct Itimerval {
struct Timeval it_interval; /* Next Value */
struct Timeval it_value; /* Current Value */
};

struct Timeval {
Long tv_sec; /* seconds */
Long tv_usec; /* microseconds */
};

--"3 modes produce different signals in 3, using similar methods

3.timerfd_create Timerfd_settime---set FD readable by time and then invoke the handler function via select polling

#include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/timerfd.h> #include     <sys/time.h> #include <sys/types.h> #include <unistd.h> #include <errno.h> #define ERR_EXIT (m)        Do {perror (M);    Exit (Exit_failure);    }while (0) int main (int argc, const char *argv[]) {struct ITIMERSPEC time;    Time.it_value.tv_sec = 5;    Time.it_interval.tv_sec = 2;    int timerfd = timerfd_create (clock_realtime, 0);    if (TIMERFD = =-1) err_exit ("Timerfd_create");    if (Timerfd_settime (TIMERFD, 0, &time, NULL) = =-1) err_exit ("Timerfd_settime");    Fd_set Read1, ready;    Fd_zero (&AMP;READ1);    Fd_set (TIMERFD, &read1);    Char buf[1024];    struct Timeval time_select;        while (1) {time_select.tv_sec = 3;//must be defined in while internal time_select.tv_usec = 11;        Ready = Read1; int nready = SELECT (Timerfd + 1, &ready, NULL, NULL, &time_select);//set to block if (Nready =-1) ERr_exit ("select");        else if (Nready = = 0) printf ("timeout"); else {if ( -1 = = Read (TIMERFD, buf, sizeof buf)) {printf ("%s\n", Strerror (Errn            o);//Print error message Err_exit ("read");        } printf ("come\n"); }} return 0;}

4. Directly using select--accurate to millisecond level

int Mssleep (Long ms) {    struct timeval TV;    tv.tv_sec = 0;    Tv.tv_usec = ms;     Return Select (0, NULL, NULL, NULL, &TV);}

Other information:

Http://www.cppblog.com/CppExplore/archive/2008/04/02/46111.html



Using Timers in Linux