Example explanation of alarm function in Linux

Introduction to Linux alarm function

Above code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
int main(int argc, char *argv[]) 
{ 
 alarm(5);
 sleep(20); 
 printf("end!\n"); 
 return 0; 
}

After running for 5 seconds, the kernel sends a SIGALRM message to the process and the process is terminated. So the result of the above program is:

Alarm clock

Of course, we can also manually define the signal processing function as follows:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <signal.h>
void sig_alarm(int sig) 
{ 
 printf("sig is %d, sig_alarm is called\n", sig);
}
int main(int argc, char *argv[]) 
{ 
 signal(SIGALRM, sig_alarm); // Register the function corresponding to the alarm signal alarm(5); // After 5 seconds, the kernel sends an alarm signal to the process and executes the corresponding signal registration function sleep(20); 
 printf("end!\n"); 
 return 0; 
}

result:

sig is 14, sig_alarm is called
end!

It can be seen that the kernel sends a SIGALRM signal to the application process and executes the corresponding registration function instead of killing the process.

It’s very simple, that’s all I have to say for now.

Summarize

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