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Noncompliant Code Example
This noncompliant code sets a signal handler while also setting a child thread to do work, which results in undefined behaviorcode example invokes the signal() function from a multithreaded program.
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <signal.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! */
thrd_t tid;
if (thrd_success != thrd_create(&tid, func, NULL)) {
/* Handle error */
}
/* ... */
return 0;
} |
Compliant Solution
This compliant solution dispenses with the signal handler and uses an object of type atomic_flag to indicate when the child thread should terminate its loop:.
| Code Block | ||||
|---|---|---|---|---|
| ||||
#include <stdatomic.h>
#include <threads.h>
atomic_flag flag = ATOMIC_VAR_INIT(0);
int func(void *data) {
while (!flag) {
/* ... */
}
return 0;
}
int main(void) {
int result;
thrd_t tid;
if (thrd_success != thrd_create(&tid, func, NULL)) {
/* Handle error */
}
/* ... */
/* Set flag when done */
while (!atomic_flag_test_and_set(&flag))
; /* Continue attempts */
return 0;
} |
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CON37-EX1: Platforms that provide defined behavior when multithreaded programs use custom signal handlers are exempt from this rule. This exception would include includes POSIX, for example.
Risk Assessment
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