rdwr.c

linux thread programe

/********************************************************
 * An example source module to accompany...
 *
 * "Using POSIX Threads: Programming with Pthreads"
 *     by Brad nichols, Dick Buttlar, Jackie Farrell
 *     O'Reilly & Associates, Inc.
 *
 ********************************************************
 * rdwr.c --
 * 
 * Library of functions implementing reader/writer locks
 */
#include <pthread.h>
#include "rdwr.h"

int pthread_rdwr_init_np(pthread_rdwr_t *rdwrp, pthread_rdwrattr_t *attrp)
{
  rdwrp->readers_reading = 0;
  rdwrp->writer_writing = 0;
  pthread_mutex_init(&(rdwrp->mutex), NULL);
  pthread_cond_init(&(rdwrp->lock_free), NULL);
  return 0;
}

int pthread_rdwr_rlock_np(pthread_rdwr_t *rdwrp){
  pthread_mutex_lock(&(rdwrp->mutex));
  while(rdwrp->writer_writing) {
    pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
  }
  rdwrp->readers_reading++;
  pthread_mutex_unlock(&(rdwrp->mutex));
  return 0;
}

int pthread_rdwr_runlock_np(pthread_rdwr_t *rdwrp)
{
  pthread_mutex_lock(&(rdwrp->mutex));
  if (rdwrp->readers_reading == 0) {
    pthread_mutex_unlock(&(rdwrp->mutex));
    return -1;
  }
  else {
    rdwrp->readers_reading--;
    if (rdwrp->readers_reading == 0) {
      pthread_cond_signal(&(rdwrp->lock_free));
    }
    pthread_mutex_unlock(&(rdwrp->mutex));
    return 0;
  }
}

int pthread_rdwr_wlock_np(pthread_rdwr_t *rdwrp)
{
  pthread_mutex_lock(&(rdwrp->mutex));
  while(rdwrp->writer_writing || rdwrp->readers_reading) {
    pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
  }
  rdwrp->writer_writing++;
  pthread_mutex_unlock(&(rdwrp->mutex));
  return 0;
}

int pthread_rdwr_wunlock_np(pthread_rdwr_t *rdwrp)
{
  pthread_mutex_lock(&(rdwrp->mutex));
  if (rdwrp->writer_writing == 0) {
    pthread_mutex_unlock(&(rdwrp->mutex));
    return -1;
  }
  else {
    rdwrp->writer_writing = 0;
    pthread_cond_broadcast(&(rdwrp->lock_free));
    pthread_mutex_unlock(&(rdwrp->mutex));
    return 0;
  }
}