Linux C Setitimer Usage notes

In Linux C programming, Setitimer is a relatively common function, can be used to implement the function of time delay and timing, the online have a variety of fragmented usage instructions, have only mentioned the individual usage, today time to practice to collate a more detailed:

header files that need to be introduced when using:

#include <sys/time.h>

Setitimer function Prototypes:

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

Where the which parameter represents the type, the optional values are:

Itimer_real: Calculates the real time of the system, it sends out the SIGALRM signal. itimer_virtual: Calculates the time spent by the process in the user state, and it sends out the SIGVTALRM signal. itimer_prof: It sends out the SIGPROF signal by the time it takes to calculate the process in both the user state and the kernel state. Immediately after the New_value and old_value are itimerval structures, first look at the definition of Itimerval structure:

struct Itimerval {struct timeval it_interval;/* Next value */struct timeval it_value;         /* Current value */};struct timeval {time_t tv_sec;        /* seconds */suseconds_t tv_usec; /* microseconds */};

Itimeval is also composed of two timeval structures, Timeval contains tv_sec and tv_usec two parts, tv_se for seconds, tv_usec for microseconds (i.e. 1/1000000 seconds)

The New_value parameter is used to set the timer, It_interval for the timing interval, it_value for the delay time, the following example shows that after the Setitimer method call succeeds, the delay of 1 microseconds triggers a SIGALRM signal, The SIGALRM signal is triggered every 200 milliseconds thereafter.

SetTimer working mechanism is, first it_value countdown, when the it_value is zero trigger signal, and then reset to It_interval, continue to It_value Countdown, has been so loop down.

Based on this mechanism, the setitimer can be used for both delayed execution and timed execution.

If the It_value is 0 will not trigger the signal, so to be able to trigger the signal, it_value more than 0, if the it_interval is zero, will only delay, not timing (that is, it will only trigger a signal).

The Old_value parameter, usually not used, is set to NULL, which is used to store the New_value value that was set when the last Setitimer call was made.

Here is a simple example of use:

#include <stdio.h> #include <signal.h> #include <sys/time.h>void signalhandler (int signo) {    Switch (signo) {case        sigalrm:            printf ("Caught the Sigalrm signal!\n");            break;   }} int main (int argc, char *argv[]) {    signal (SIGALRM, signalhandler);    struct Itimerval new_value, old_value;    new_value.it_value.tv_sec = 0;    New_value.it_value.tv_usec = 1;    new_value.it_interval.tv_sec = 0;    New_value.it_interval.tv_usec = 200000;    Setitimer (Itimer_real, &new_value, &old_value);        for (;;);         return 0;}

Reference Links:

Http://man7.org/linux/man-pages/man2/setitimer.2.html