/* Code Example 4 */

#include <pthread.h>
#include <signal.h>

void* sig_handler( void* );

/* global variable used to indicate what signal (if any)
 * has been caught
 */
int handled_signal = -1;

/* mutex to be used whenever accessing the above global data */ 
pthread_mutex_t sig_mutex = PTHREAD_MUTEX_INITIALIZER;

int main(void )
{
        sigset_t signal_set;
        pthread_t sig_thread;

        /* block all signals */
        sigfillset( &signal_set );
        pthread_sigmask( SIG_BLOCK, &signal_set, NULL );

        /* create the signal handling thread */
        pthread_create( &sig_thread, NULL, sig_handler, NULL );

        for (;;) {
                /* whatever you want your program to do... */

                /* grab the mutex before looking at handled_signal */
                pthread_mutex_lock( &sig_mutex );

                /* look to see if any signals have been caught */
                switch ( handled_signal )
                {
                case -1:
                        /* no signal has been caught by the signal handler */
                        break;

                case 0:
                        printf( "The signal handler caught a signal"
                                "I'm not interested in (%d)\n",
                                handled_signal );
                        handled_signal = -1;
                        break;

                case SIGQUIT:
                        printf( "The signal handler caught a SIGQUIT signal!\n" );
                        handled_signal = -1;
                        break;

                case SIGINT:
                        printf( "The signal handler caught a SIGINT signal!\n" );
                        handled_signal = -1;
                        break;
                }
                /* remember to release the mutex */
                pthread_mutex_unlock( &sig_mutex );
        }
}

void* sig_handler( void* arg )
{
        sigset_t signal_set;
        int sig;

        for(;;) {
                /* wait for any and all signals */
                sigfillset( &signal_set );
                sigwait( &signal_set, &sig );

                /* when we get this far, we've caught a signal */

                switch( sig )
                {
                case SIGQUIT:  /* whatever you need to do on SIGQUIT */
                        pthread_mutex_lock( &sig_mutex );
                        handled_signal = SIGQUIT;
                        pthread_mutex_unlock( &sig_mutex );
                        break;

                case SIGINT:  /* whatever you need to do on SIGINT */
                        pthread_mutex_lock( &sig_mutex );
                        handled_signal = SIGINT;
                        pthread_mutex_unlock( &sig_mutex );
                        break;

                default:   /* whatever you need to do for other signals */
                        pthread_mutex_lock( &sig_mutex );
                        handled_signal = 0;
                        pthread_mutex_unlock( &sig_mutex );
                        break;
                }
        }
        return (void*)0;
}