TVH Queue Example

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include "queue.h"

/* Struct containing entries to go in the queue
 * TODO: add you're fields
 * TODO: name sensibly
 */
typedef struct queue_entry
{
  TAILQ_ENTRY(queue_entry) link;
  // Add working fields
  int data;
} queue_entry_t; // Name appropriately

/* Queue, Cond to signal data and Mutex to protect it */
static TAILQ_HEAD(,queue_entry) queue;
static pthread_mutex_t          mutex;
static pthread_cond_t           cond;

/*
 * Basic pattern for a queue driven thread
 */
void *a_thread ( void *aux )
{
  queue_entry_t *qe;
  pthread_mutex_lock(&mutex);

  while (1) { // do you need an exit condition - probably not

    /* Get entry from queue */
    qe = TAILQ_FIRST(&queue);
    if (!qe) { // Queue empty
      pthread_cond_wait(&cond, &mutex); // Note: this will unlock mutex
                                        //       on entry and lock on exit
      continue;                         // Go back to get entry (or if exit)
    }
    TAILQ_REMOVE(&queue, qe, link);     // Remove entry and we're done with Q
    pthread_mutex_unlock(&mutex);       // now other threads can add while
                                        // we process

    // TOOD: DO SOME WORK
    printf("DATA: %d\n", qe->data);
  }

  // Cannot reach here unless you have exit condition
  return NULL;
}

/*
 * Initialise
 */
void init ( void )
{
  pthread_t tid; // you probably don't need to keep this

  pthread_mutex_init(&mutex, NULL); // Use default config
  pthread_cond_init(&cond, NULL);   // ditto

  /* Start thread - presumably permanently active */
  pthread_create(&tid, NULL, a_thread, NULL); // last param is passed as aux
                                              // as this is single global
                                              // you can probably use global
                                              // vars
}

/*
 * Add data to the queue
 *
 * TODO: you can either have user pass in just the "data"
 *       or a full queue_entry_t but you'd need to define struct in header
 */
void add ( int data )
{
  /* Create entry */
  queue_entry_t *qe = calloc(1, sizeof(queue_entry_t));
  qe->data = data;

  /* Insert */
  pthread_mutex_lock(&mutex);
  TAILQ_INSERT_TAIL(&queue, qe, link);
  pthread_cond_signal(&cond); // tell thread data is available
  pthread_mutex_unlock(&mutex);
}