8. Using sigprocmask for Signal Blocking

pravjot

8. Using sigprocmask for Signal Blocking

Explain the purpose of the sigprocmask function in Unix-like operating systems. Describe its syntax and how it can be used to block and unblock signals, providing an example to block SIGINT.

gaurav133232

The sigprocmask function masks a signal i.e. blocks it and unblocks it. Its syntax is :-

int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

how: how describes how the signal will be masked, it can be one of the following:-

SIG_BLOCK: Adds the signals specified in set to the current signal mask.
SIG_UNBLOCK: Removes the signals specified in set from the current signal mask.
SIG_SETMASK: Replaces the current signal mask with the signals specified in set.

set: points to the set of signals to be added, removed or assigned to the current signals.

oldset: If not 'NULL', the previous value of the signal mask is stored in the location pointed to by oldset.

if we want to block a signal, we'll use SIG_BLOCK and if we want to unblock it, we'll use SIG_UNBLOCK.

Here's an example:-

#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");

// Loop indefinitely

while (1)

{

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

sleep(1);

}

return 0;

}

8. Using sigprocmask for Signal Blocking

8. Using sigprocmask for Signal Blocking

Explain the purpose of the sigprocmask function in Unix-like operating systems. Describe its syntax and how it can be used to block and unblock signals, providing an example to block SIGINT.

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