Wednesday, October 27, 2021

[SOLVED] Signal Management, when Send Command kill

Issue

So iam developing a program that when receive a signal kill -SIGUSR1 PID, need to output to stdout the following line:

2020-10-09T18:01:27+01:00, and this is the time, when programm was launched, so I need to get this time when the signal is received! I am using siginfo

I dont need to know how to print, I need to know how to get the time when the program was launched!

act.sa_sigaction = signalManagement;

sigemptyset(&act.sa_mask);

act.sa_flags |= SA_SIGINFO; 
act.sa_flags |= SA_RESTART; 


if (sigaction(SIGUSR1 , &act, NULL) < 0){
    ERROR(1, "sigaction - SIGUSR1 ");
}

and my signal function is:

void signalManagement(int sig, siginfo_t *siginfo, void *context) 
{
    (void)context;
    int aux;
    aux = errno;

    if(sig == SIGUSR1 ){
      //* I need code where to show the output "2020-10-09T18:01:27+01:00", example when programm was launched
    }

    errno = aux;
}

Solution

I need to know how to get the time when the program was launched!

So store the time at your program startup and print it when receiving the signal.

#include <time.h>
#include <stdio.h>
#include <stddef.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
static sig_atomic_t sigusr1_received = 0;
static void sigusr1_handler(int v) {
    ++sigusr1_received;
}
int main() {
    struct tm startuptime = *localtime((time_t[1]){time(0)});
    signal(SIGUSR1, sigusr1_handler);
    while (1) {
        pause();
        if (sigusr1_received) {
            --sigusr1_received;
            char buf[200];
            strftime(buf, sizeof(buf), "%FT%X%z", &startuptime);
            printf("%s\n", buf);
        }
    }
}

Adding the additional : two characters from the back is left as an exerciser to others. One could also call strftime once at program startup and call write(3) from signal handler. Like so:

#include <time.h>
#include <signal.h>
#include <unistd.h>
#include <string.h>
static char buf[200];
void sigusr1_handler(int v) {
    write(STDOUT_FILENO, buf, strlen(buf));
}
int main() {
    strftime(buf, sizeof(buf), "%FT%X%z\n", localtime((time_t[1]){time(0)}));
    signal(SIGUSR1, sigusr1_handler);
    while (1) {
        pause();
    }
}


Answered By - KamilCuk
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