Threads are created, then all exit before critical region - c

Question

I need to write a program for class that creates 8 threads. 4 producer, and 4 consumer. The producers need to loop, and randomly send SIGUSR1 or SIGUSR2 to all consumer threads. Only 2 should register if they have received SIGUSR1 and the other 2 register SIGUSR2.
When I try to run it all threads are created, "prod ready" is printed by all 4 producer threads,"waiting 1" is printed by both threads, but "waiting 2" is printed 3 times then all threads exit. At the end of debugging it says that the process exits normally.
I need to use semaphores to control the critical regions. Any help would be great.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <semaphore.h>
#include <signal.h>
#define NP 4
#define NC1 2
#define NC2 2
#define CNT 10
void handler1(int signum);
void handler2(int signum);
typedef struct {
int sent;
int received;
int buf[1];
int SIG1;
int SIG2;
sem_t con;
sem_t prod;
} sbuf_t;
sbuf_t buff;
void *producer() {
printf("prod ready \n");
int s;
while(1){
sem_wait(&buff.prod);
s=rand()%2;
if(s==1){
buff.sent++;
kill(0,SIGUSR1);
}
else if(s==2){
buff.sent++;
kill(0,SIGUSR2);
}sem_post(&buff.prod);
}
}
void *consumer1() {
signal(SIGUSR1, handler1);
printf("waiting 1\n");
while(1){
}
}
void *consumer2() {
signal(SIGUSR2, handler2);
printf("waiting 2\n");
while(1){
}
}
void handler1(int signum){
if(signum==SIGUSR1){
sem_wait(&buff.con);
printf("Caught 1\n");
buff.received++;
buff.SIG1++;
sem_post(&buff.con);
}
}
void handler2(int signum){
if(signum==SIGUSR2){
sem_wait(&buff.con);
printf("caught 2 \n");
buff.received++;
buff.SIG2++;
sem_post(&buff.con);
}
}
void main(){
pthread_t threads[9];
buff.SIG1=0;
buff.SIG2=0;
buff.sent=0;
buff.received=0;
int index;
sem_init(&buff.con, 0, 0);
sem_init(&buff.prod, 0, 0);
for (index = 0; index < NP; index++) {
pthread_create(&threads[index], NULL, producer,NULL);
}
for (index = 0;index < NC1;index++) {
pthread_create(&threads[index+4], NULL, consumer1,NULL);
}
for (index = 0;index < NC2;index++) {
pthread_create(&threads[index+6], NULL, consumer2,NULL);
}
}

Answer 1

In the main() function, the threads are being created,
then main() exits.
When main() exits, all the threads are also exited.
Suggest reading about such functions as: pthread_exit() and pthread_join()
Note: the following has an error in the handling of the signals and in the handling of the semaphores, but will demonstrate the use of pthread_join() and pthread_exit()
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <semaphore.h>
#include <signal.h>
#define NP 4
#define NC1 2
#define NC2 2
#define CNT 10
#define MAX_THREADS (9)
void handler1(int signum);
void handler2(int signum);
struct sbuf_t
{
int sent;
int received;
int buf[1];
int SIG1;
int SIG2;
sem_t con1;
sem_t con2;
sem_t prod;
};
typedef struct sbuf_t myData;
myData buff;
void *producer( void *dummy )
{
(void)dummy;
printf("prod ready \n");
int s;
while(1)
{
sem_wait(&buff.prod);
s=rand()%2;
if( !s )
{
buff.sent++;
kill( 0, SIGUSR1 );
}
else // if( s )
{
buff.sent++;
kill( 0, SIGUSR2 );
}
//sem_post(&buff.prod);
}
pthread_exit( NULL );
} // end thread: producer
void *consumer1( void *dummy )
{
(void)dummy;
//signal(SIGUSR1, handler1);
printf("waiting 1\n");
while(1)
{
sem_wait( &buff.con1 );
// do something
//sem_post( &buff.prod );
}
pthread_exit( NULL );
} // end thread: consumer1
void *consumer2( void *dummy )
{
(void)dummy;
//signal(SIGUSR2, handler2);
printf("waiting 2\n");
while(1)
{
sem_wait( &buff.con2 );
// do something
//sem_post( &buff.prod );
}
pthread_exit( NULL );
} // end thread: consumer2
void handler(int signum)
{
sem_post(&buff.prod);
if(signum==SIGUSR1)
{
//sem_wait(&buff.con);
puts("Caught 1");
buff.received++;
buff.SIG1++;
sem_post(&buff.con1);
}
else if(signum==SIGUSR2)
{
//sem_wait(&buff.con);
puts("caught 2");
buff.received++;
buff.SIG2++;
sem_post(&buff.con2);
}
} // end signal handler: handler2
int main( void )
{
pthread_t threads[ MAX_THREADS ];
buff.SIG1=0;
buff.SIG2=0;
buff.sent=0;
buff.received=0;
int index;
sem_init(&buff.con1, 0, 0);
sem_init(&buff.con2, 0, 0);
sem_init(&buff.prod, 0, 0);
signal(SIGUSR2, handler);
signal(SIGUSR1, handler);
for (index = 0; index < NP; index++)
{
pthread_create(&threads[index], NULL, producer,NULL);
}
for (index = 0;index < NC1;index++)
{
pthread_create(&threads[index+4], NULL, consumer1,NULL);
}
for (index = 0;index < NC2;index++)
{
pthread_create(&threads[index+6], NULL, consumer2,NULL);
}
for( size_t x=0; x<MAX_THREADS; x++ )
{
pthread_join( threads[x], NULL );
}
} // end function: main
HOWEVER, the methods to handle signals to threads does not use kill() as that is for processes.
rather the code should use functions similar to::
int pthread_cond_wait(pthread_cond_t *restrict cond, pthread_mutex_t *restrict mutex);
int pthread_cond_signal(pthread_cond_t *cond)
The signaled thread should block on a pthread_cond_wait() call until another thread sends a signal using pthread_cond_signal(), with the same condition variable.
Considering the analogy with signals delivered to processes, this is a bit different because the signaled thread has already suspended its execution waiting for a signal, unlike a process that simply gets interrupted and goes on.

Answer 2

For you example, you are creating your producers before your consumers. Also in your producer, you are using a random number generator to determine if you issue USR1 or USR2. Your description gave the impression you wanted two of each (versus some random mix totaling 4) which is what I see the code doing for you.