Question

I have the following code and it is being killed by a SEGV signal. Using the debugger shows that it is being killed by the first sem_init() in main(). If I comment out the first sem_init() the second causes the same problem. I have tried figuring out what would cause this sys call to cause a SEGV. The else is not being run, so the error is happening before it can return a value.
Any help would be greatly appreciated,
Thank you.

I removed the rest of the code that isnt being run before this problem occurs.

#define PORTNUM 7000
#define NUM_OF_THREADS 5
#define oops(msg) { perror(msg); exit(1);}
#define FCFS 0
#define SJF 1;

void bindAndListen();
void acceptConnection(int socket_file_descriptor);
void* dispatchJobs(void*);
void* replyToClient(void* pos);

//holds ids of worker threads
pthread_t threads[NUM_OF_THREADS];

//mutex variable for sleep_signal_cond
pthread_mutex_t sleep_signal_mutex[NUM_OF_THREADS];
//holds the condition variables to signal when the thread should be unblocked
pthread_cond_t sleep_signal_cond[NUM_OF_THREADS];

//mutex for accessing sleeping_thread_list
pthread_mutex_t sleeping_threads_mutex = PTHREAD_MUTEX_INITIALIZER;
//list of which threads are sleeping so they can be signaled and given a job
std::vector<bool> *sleeping_threads_list = new std::vector<bool>();

//number of threads ready for jobs
sem_t* available_threads;
sem_t* waiting_jobs;


//holds requests waiting to be given to one of the threads for execution
std::vector<std::vector<int> >* jobs = new std::vector<std::vector<int> >();

pthread_mutex_t jobs_mutex = PTHREAD_MUTEX_INITIALIZER;




int main (int argc, char * const argv[]) {

//holds id for thread responsible for removing jobs from ready queue and assigning them to worker thread
pthread_t dispatcher_thread;


//initializes semaphores
    if(sem_init(available_threads, 0, NUM_OF_THREADS) != 0){          //this is the line causing the SEGV
        oops("Error Initializing Semaphore");
    }

    if(sem_init(waiting_jobs, 0, 0) !=0){
        oops("Error Initializing Semaphore");
    }


//initializes condition variables and guarding mutexes
for(int i=0; i<NUM_OF_THREADS; i++){
    pthread_cond_init(&sleep_signal_cond[i], NULL);
    pthread_mutex_init(&sleep_signal_mutex[i], NULL);
}




if(pthread_create(&dispatcher_thread, NULL, dispatchJobs, (void*)NULL) !=0){
    oops("Error Creating Distributer Thread");

Answer 1

You declare pointers to your semaphores:

sem_t* available_threads;
sem_t* waiting_jobs;

but never initialize the memory. The sem_init function is not expecting to allocate memory, just to initialize an existing blob of memory. Either allocate some memory and assign these pointers to it, or declare the semaphores as sem_t and pass the address to sem_init.