kqueue-EVFILT_SIGNAL-test.c

/**
 * Check for raising a signal before looping:
 * - OSX 10.14 -- *SIGALARM* (with USE__RAISE/USE__PTHREAD_KILL), exit cleanly with USE__KILL
 * - OSX 10.11 -- exit cleanly (with USE__RAISE/USE__PTHREAD_KILL/USE__KILL)
 */

#include <sys/event.h>
#include <unistd.h>
#include <assert.h>
#include <signal.h>
#include <stdio.h>

int main (int argc, const char *argv[])
{
    int kq = kqueue();

    struct kevent sigevent;
    EV_SET(&sigevent, SIGINT, EVFILT_SIGNAL, EV_ADD | EV_ENABLE, 0, 0, NULL);
    signal(SIGINT, SIG_IGN);
    kevent(kq, &sigevent, 1, NULL, 0, NULL);

#if defined(USE__RAISE)
    raise(SIGINT);
#elif defined(USE__PTHREAD_KILL)
    raise(SIGINT);
#elif defined(USE__KILL)
    kill(getpid(), SIGINT);
#else
# error "One of USE__RAISE/USE__PTHREAD_KILL/USE__KILL should be specified"
#endif
    alarm(1);

    struct kevent change;
    assert(kevent(kq, NULL, 0, &change, 1, NULL) != -1);
    assert(!change.udata);
    puts("Signal received. Clean exit.");

    close(kq);
    return 0;
}

Apple says:

kevent listens to process-targeted signals, not thread-targeted signals.
“Only signals sent to the process, not to a particular thread, will trigger the filter.”

And:

https://pubs.opengroup.org/onlinepubs/7908799/xsh/raise.html


The raise() function sends the signal sig to the executing thread.
The effect of the raise() function is equivalent to calling:

pthread_kill(pthread_self(), sig);

So, this behaves correctly.