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#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
// from stack overflow
// https://stackoverflow.com/questions/6326290/about-the-ambiguous-description-of-sigwait
// except the deliberate errors
static int sig_count;
void on_sigusr1(int sig)
{
++sig_count;
}
int main(void)
{
// Set a signal handler for SIGUSR1
signal(SIGUSR1, &on_sigusr1);
// At program startup, SIGUSR1 is neither blocked nor pending, so raising it
// will call the signal handler
raise(SIGUSR1);
// Now let's block SIGUSR1
sigset_t* psigset = malloc(sizeof(sigset_t));
sigemptyset(psigset);
sigaddset(psigset, SIGUSR1);
sigprocmask(SIG_BLOCK, psigset, NULL);
// SIGUSR1 is now blocked, raising it will not call the signal handler
raise(SIGUSR1);
// SIGUSR1 is now blocked and pending -- this call to sigwait will return
// immediately
int sig;
int result = sigwait(psigset, &sig);
if(result == 0)
printf("sigwait got signal: %d\n", sig);
// SIGUSR1 is now no longer pending (but still blocked). Raise it again and
// unblock it
raise(SIGUSR1);
printf("About to unblock SIGUSR1\n");
sigprocmask(SIG_UNBLOCK, psigset, NULL);
printf("Unblocked SIGUSR1\n");
assert(sig_count == 2);
// now a couple of bad params
// reblock
sigprocmask(SIG_BLOCK, psigset, NULL);
raise(SIGUSR1);
int* psig = malloc(sizeof(int));
free(psig);
result = sigwait(psigset, psig);
free(psigset);
raise(SIGUSR1);
result = sigwait(psigset, &sig);
return 0;
}
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