CERT C: Rec. SIG02-C

Avoid using signals to implement normal functionality

Since R2026a

Description

Avoid using signals to implement normal functionality.¹

Polyspace Implementation

The rule checker checks for Use of standard header file signal.h.

Examples

Use of standard header file signal.h

Issue

This issue occurs if you use the functionalities from the standard header signal.h. If the signal function is a macro and the macro is expanded in the code, Polyspace^® reports a violation.

Risk

Using signal handling functions can cause implementation-defined and undefined behavior.

Fix

Use alternatives such as the concurrency libraries from POSIX or C11.

Example

In this example, Polyspace reports violations on the use of signals for synchronizing two threads.

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <signal.h>  //Noncompliant
#include <unistd.h>

volatile sig_atomic_t signal_received = 0;

void signal_handler(int signum) {
    signal_received = 1;
}

void* thread_func_1(void* arg) {
    printf("Thread 1: Doing some work...\n");
    // Work....
    printf("Thread 1: Sending signal to thread 2.\n");
    pthread_kill(*(pthread_t*)arg, SIGUSR1);
    return NULL;
}

void* thread_func_2(void* arg) {
    signal(SIGUSR1, signal_handler);  //Noncompliant
    printf("Thread 2: Waiting for signal...\n");
    while (!signal_received) {
        pause();  // Wait for signal
    }
    printf("Thread 2: Signal received, proceeding with work.\n");
    return NULL;
}

Correction

Use alternatives, such as mutexes and condition variables from the C11 concurrency library, for synchronizing threads.

#include <stdio.h>
#include <stdlib.h>
#include <threads.h>  //Compliant

mtx_t mutex;
cnd_t condition;
int signal_received = 0;

int thread_func_1(void* arg) {
    printf("Thread 1: Doing some work...\n");
    thrd_sleep(&(struct timespec){.tv_sec = 2}, NULL);  
    printf("Thread 1: Signaling thread 2.\n");

    mtx_lock(&mutex);
    signal_received = 1;
    cnd_signal(&condition);
    mtx_unlock(&mutex);

    return 0;
}

int thread_func_2(void* arg) {
    mtx_lock(&mutex);
    while (!signal_received) {
        printf("Thread 2: Waiting for signal...\n");
        cnd_wait(&condition, &mutex);
    }
    printf("Thread 2: Signal received, proceeding with work.\n");
    mtx_unlock(&mutex);

    return 0;
}

Check Information

Group: Rule 11. Signals (SIG)

PQL Name: std.cert.SIG02_C

Version History

Introduced in R2026a