Asynchronous Safety with sig_atomic_t

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Asynchronous Safety with sig_atomic_t

'sig_atomic_t' is an integer type that can be accessed as an atomic entity even in the presence of asynchronous interrupts (signals). Combined with 'volatile', it prevents the compiler from caching the variable in a register, ensuring the main loop sees the update made by the signal handler.

snippet.c
c
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
 
volatile sig_atomic_t keep_running = 1;
 
void handle_sigint(int sig) {
    keep_running = 0;
}
 
int main() {
    signal(SIGINT, handle_sigint);
    printf("Running loop. Press Ctrl+C to stop...\n");
    
    while (keep_running) {
        // Simulate work
    }
    
    printf("Clean exit.\n");
    return 0;
}

Breakdown

volatile sig_atomic_t keep_running

Guarantees that reads/writes are atomic relative to signals and bypasses compiler optimizations.

keep_running = 0;

Safe to execute inside a signal handler because the operation is guaranteed to be atomic.

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Asynchronous Safety with sig_atomic_t

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