How to use pthreads barrier?

Question

Hi Sorry for sending a big dump of code, but I'm very new to C code, basically I am doing college assignment and I need to implement "pthread_barrier", now I understand the concept of a barrier (or at least I think I know ) But I don’t know exactly where. Appointment:

"Use pthread_barrier_init and pthread_barrier_wait to ensure that all producer / consumer flows begin to produce / consume at the same time."

This is an additional credit part of the assignment by

#include <pthread.h> #include <stdlib.h> #include <unistd.h> #include <stdio.h> #define SIXTY_SECONDS 60000000 #define ONE_SECOND 1000000 #define RANGE 10 #define PERIOD 2 typedef struct { int *carpark; int capacity; int occupied; int nextin; int nextout; int cars_in; int cars_out; pthread_mutex_t lock; pthread_cond_t space; pthread_cond_t car; pthread_barrier_t bar; } cp_t; /* Our producer threads will each execute this function */ static void * producer(void *cp_in) { cp_t *cp; unsigned int seed; /* Convert what was passed in to a pointer to a bounded buffer */ cp = (cp_t *)cp_in; /* Loop */ while (1) { /* Sleep for up to 1s */ usleep(rand_r(&seed) % ONE_SECOND); /* Acquire the lock */ pthread_mutex_lock(&cp->lock); /* While full wait until there is room available */ while (cp->occupied == cp->capacity) { pthread_cond_wait(&cp->car, &cp->lock); } /* Insert an item */ cp->carpark[cp->nextin] = rand_r(&seed) % RANGE; /* Increment counters */ cp->occupied++; cp->nextin++; cp->nextin %= cp->capacity; cp->cars_in++; /* Someone may be waiting on data to become available */ pthread_cond_signal(&cp->space); /* Release the lock */ pthread_mutex_unlock(&cp->lock); } return ((void *)NULL); } /* Our consumer threads will each execute this function */ static void * consumer(void *cp_in) { cp_t *cp; unsigned int seed; /* Convert what was passed in to a pointer to a bounded buffer */ cp = (cp_t *)cp_in; while (1) { /* Sleep for up to 1s */ usleep(rand_r(&seed) % ONE_SECOND); /* Acquire the lock */ pthread_mutex_lock(&cp->lock); /* While empty wait until there is data available */ while (cp->occupied == 0) { pthread_cond_wait(&cp->space, &cp->lock); } /* Increment counters */ cp->occupied--; cp->nextout++; cp->nextout %= cp->capacity; cp->cars_out++; /* Someone may be waiting on room to become available */ pthread_cond_signal(&cp->car); /* Release the lock */ pthread_mutex_unlock(&cp->lock); } return ((void *)NULL); } /* Our monitor thread will each execute this function */ static void * monitor(void *cp_in) { cp_t *cp; /* Convert what was passed in to a pointer to a bounded buffer */ cp = (cp_t *)cp_in; while (1) { /* Pause */ sleep(PERIOD); /* Acquire the lock */ pthread_mutex_lock(&cp->lock); printf("Delta: %d\n", cp->cars_in - cp->cars_out); /* Release the lock */ pthread_mutex_unlock(&cp->lock); } return ((void *)NULL); } /* Initialisation */ static int init(cp_t *cp, int capacity) { /* Set up the bounded buffer internals */ cp->occupied = cp->nextin = cp->nextout = cp->cars_in = cp->cars_out = 0; cp->capacity = capacity; /* Initialise our data structure */ cp->carpark = (int *)malloc(cp->capacity * sizeof (*cp->carpark)); /* Check malloc succeeded */ if (cp->carpark == NULL) { perror("malloc()"); exit(EXIT_FAILURE); } /* Initialise lock and condition variables */ pthread_mutex_init(&cp->lock, NULL); pthread_cond_init(&cp->space, NULL); pthread_cond_init(&cp->car, NULL); /* Seed random number generator */ srand((unsigned int)getpid()); return (0); } int main(int argc, char *argv[]) { pthread_t p, c, m; cp_t cp; /* Check usage */ if (argc != 2) { printf("Usage: %s buffer_size\n", argv[0]); exit(EXIT_FAILURE); } /* Initialise */ init(&cp, atoi(argv[1])); /* Create our threads */ pthread_create(&p, NULL, producer, (void *)&cp); pthread_create(&p, NULL, producer, (void *)&cp); pthread_create(&c, NULL, consumer, (void *)&cp); pthread_create(&c, NULL, consumer, (void *)&cp); pthread_create(&m, NULL, monitor, (void *)&cp); /* Wait for our threads */ pthread_join(p, NULL); pthread_join(p, NULL); pthread_join(c, NULL); pthread_join(c, NULL); pthread_join(m, NULL); return (0); } 

Answer 1

I could give you the full answer, but I am afraid of Lasse W. Carlsen. Therefore, I will give you clues.

• The barrier object bar already available in struct cp_t
• Initialize it with pthread_barrier_init , for example, you initialized mutexes. There is a correspondence between count and the number of participants.
• Both producers and consumers must wait before starting to produce / consume. Get it?