#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/types.h>
#include <signal.h>
#include <semaphore.h>

#define THREADS 3

int threads;
sem_t sem;

void signal_usr1_act(int signo,siginfo_t *inf,void *vd)
{
pthread_t *s;
fprintf(stderr,"Got USR1\n");
s=inf->si_value.sival_ptr;
pthread_join(*s,NULL);
threads--;
fprintf(stderr,"Joined!\n");
if(threads==0)sem_post(&sem);
}

void *thread_func(void*a)
{
union sigval sig_value;
sig_value.sival_ptr=a;
fprintf(stderr,"sending signal\n");
sigqueue(getpid(),SIGUSR1,sig_value); // sending pthread_t*
fprintf(stderr,"sleeping\n");
system("sleep 2"); // Any operation to make a delay
fprintf(stderr,"Stop sleeping\n");
}

int main(int argc,char **argv)
{
int i;
pthread_t pts[THREADS];
sigset_t new_mask,old_mask;
struct sigaction new_sig,old_sig;
// Adding signal action
new_sig.sa_sigaction=signal_usr1_act;
new_sig.sa_flags=SA_SIGINFO;
sigemptyset(&new_sig.sa_mask);
sigfillset(&new_sig.sa_mask);
sigaction(SIGUSR1,&new_sig,&old_sig);
// some initialisation stuff
sem_init(&sem,0,0);
threads=THREADS;
// creating mask
sigemptyset(&new_mask);
sigfillset(&new_mask);
// creating threads
pthread_sigmask(SIG_BLOCK,&new_mask,&old_mask);
for(i=0;i<THREADS;i++)
{
pthread_create(pts+i,NULL,thread_func,pts+i);
// And some other code, where we should block signals
}
pthread_sigmask(SIG_SETMASK,&old_mask,NULL);
// Waiting for threads
do{
pthread_sigmask(SIG_BLOCK,&new_mask,NULL);
fprintf(stderr,"Main is locked! Waiting for %d threads\n",threads);
pthread_sigmask(SIG_SETMASK,&old_mask,NULL);
}while(sem_wait(&sem)<0);
sem_destroy(&sem);
return 0;
}

Main is locked! Waiting for 3 threads
sending signal
sleeping
Got USR1
sending signal
sleeping
sending signal
sleeping
Stop sleeping
Stop sleeping
Joined!
Got USR1
Joined!
Main is locked! Waiting for 1 threads
Stop sleeping