For MacOS pthreads, sigwait() Does Not Handle a Signal - macos

Question

When running the following, the sigwait() never handles the SIGUSR1 signal. Basic setup is: main spawns two pthreads: one a handler thread and one a worker thread. The main thread and both spawned threads block SIGUSR1. The worker raises SIGUSR1 twice with a two second delay. The handler thread never sees it.
This is on MacOS. When running from Xcode I insert a continuable breakpoint that executes pro hand -p true -s false SIGUSR1. If I run the executable from the command line, the same output occurs.
Why does sigwait() not see the raised SIGUSR1?
Here is the output:
SigHandlerThread: Waiting: 30
Raise
Raise
Program ended with exit code: 0
Here is the code:
//
// Signal Test
//
typedef void* (*ThreadRoutine) (void*); // pthread_create
void workerRaise (int signum) {
sleep (2);
printf ("Raise\n");
raise (signum);
}
void sigBlock (sigset_t *set, int signum) {
sigemptyset(set);
sigaddset(set, signum);
pthread_sigmask(SIG_BLOCK, set, NULL);
}
void *sigHandlerThread (void *ignore) {
int signal;
sigset_t blockSignalSet;
sigBlock(&blockSignalSet, SIGUSR1);
printf ("SigHandlerThread: Waiting: %d\n", SIGUSR1);
while (0 == sigwait(&blockSignalSet, &signal))
printf ("SigHandlerThread: %d\n", signal);
printf ("SigHandlerThread: Exit (0 != sigwait())\n");
return NULL;
}
void *workerThread (void *ignore) {
sigset_t blockSignalSet;
sigBlock(&blockSignalSet, SIGUSR1);
workerRaise(SIGUSR1);
workerRaise(SIGUSR1);
pthread_exit(NULL);
}
// Called from main.
void testSignal () {
sigset_t blockSignalSet;
sigBlock(&blockSignalSet, SIGUSR1);
pthread_t worker, handler;
pthread_create (&handler, NULL, (ThreadRoutine) sigHandlerThread, NULL);
pthread_create (&worker, NULL, (ThreadRoutine) workerThread, NULL);
pthread_join(worker, NULL);
sleep (2);
}

Answer 1

The raise() function sends the signal directed specifically at the calling thread - other threads in the process won't receive it. raise(signum) is equivalent to pthread_kill(pthread_self(), signum).
What you need is a process-directed signal, not a thread-directed signal. Instead of using raise(signum), use kill(getpid(), signum).