Calling the signal() function in a multithreaded program is undefined behavior. (see See undefined behavior 135.).
Noncompliant Code Example
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#include <signal.h>
#include <stddef.h>
#include <threads.h>
volatile sig_atomic_t flag = 0;
void handler(int signum) {
flag = 1;
}
/* Runs until user sends SIGUSR1 */
int func(void *data) {
while (!flag) {
/* ... */
}
return 0;
}
int main(void) {
signal(SIGUSR1, handler); /* Undefined behavior */
thrd_t tid;
if (thrd_success != thrd_create(&tid, func, NULL)) {
/* Handle error */
}
/* ... */
return 0;
} |
NOTE: The SIGUSR1 signal value is not defined in the C Standard; consequently, this is not a C-compliant code example.
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