10. Practical Example of Signal Blocking

pravjot

10. Practical Example of Signal Blocking

Walk through the example program that blocks the SIGINT signal for 10 seconds and then unblocks it. Explain the steps involved in setting up the signal handler, blocking the signal, and handling it after unblocking.

gaurav133232

#include <stdio.h>

#include <stdlib.h>

#include <signal.h>

#include <unistd.h>

void handle_signal(int sig)

{

printf("Caught signal %d\n", sig);

}

int main()

{

struct sigaction sa;

sa.sa_handler = handle_signal;

sa.sa_flags = 0; // No flags

sigemptyset(&sa.sa_mask);

// Set up the signal handler for SIGINT

if (sigaction(SIGINT, &sa, NULL) == -1)

{

perror("sigaction");

exit(EXIT_FAILURE);

}

sigset_t mask, oldmask;

// Initialize the signal set to empty

sigemptyset(&mask);

// Add SIGINT to the signal set

sigaddset(&mask, SIGINT);

// Block SIGINT and save the old signal mask

if (sigprocmask(SIG_BLOCK, &mask, &oldmask) == -1)

{

perror("sigprocmask");

exit(EXIT_FAILURE);

}

printf("SIGINT blocked. Try pressing Ctrl+C...\n");

sleep(10); // SIGINT is blocked during this sleep

// Restore the old signal mask, unblocking SIGINT

if (sigprocmask(SIG_SETMASK, &oldmask, NULL) == -1)

{

perror("sigprocmask");

exit(EXIT_FAILURE);

}

printf("SIGINT unblocked. Press Ctrl+C now...\n");

while (1)

{

printf("Running...\n");

sleep(1);

}

return 0;

}

gaurav133232

What happens in the above program is:-

Firstly, the signal handler is set to handle SIGINT.
The sigaction call sets up the signal handler for SIGINT.
SIGINT is blocked by using sigaddset(&mask,SIGINT) adds SIGINT to the signal set.
sigprocmask(SIG_BLOCK,&mask,&oldmask) blocks sigint and saves the current signal mask in oldmask.
Then in criticals section the program is on sleep for 10 seconds . During this period , pressing ctrl+C won't interrupt the program because SIGINT is blocked.
sigprocmask(SIG_SETMASK,&oldmask,NULL) restores the old signal mask, unblocking SIGINT.
Since we have used an infinite loop at the end, the program will keep printing the statement in loop, just when ctrl+c is pressed, it will print the statement in the signal handler section, which will print caught signal 2.

10. Practical Example of Signal Blocking

10. Practical Example of Signal Blocking

Walk through the example program that blocks the SIGINT signal for 10 seconds and then unblocks it. Explain the steps involved in setting up the signal handler, blocking the signal, and handling it after unblocking.

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