_rw_locks.c

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

int 
rw_init(struct rw_lock_t *rw)
{
  struct rw_lock_t temp={0,0,PTHREAD_MUTEX_INITIALIZER,PTHREAD_MUTEX_INITIALIZER,PTHREAD_COND_INITIALIZER,PTHREAD_MUTEX_INITIALIZER,PTHREAD_COND_INITIALIZER};

  /* if ((temp = (struct rw_lock_t*) malloc(sizeof(struct rw_lock_t))) == NULL) { */
  /*   perror("Malloc failed."); */
  /*   exit(1); */
  /* } */

  /* temp->readers = 0; */
  /* temp->writers = 0; */
  /* /\* temp->WriterConditionMutex = PTHREAD_MUTEX_INITIALIZER; *\/ */
  /* /\* temp->WriterMutex = PTHREAD_MUTEX_INITIALIZER; *\/ */
  /* /\* temp->WriterCondition = PTHREAD_COND_INITIALIZER; *\/ */
  /* /\* temp->ReaderConditionMutex = PTHREAD_MUTEX_INITIALIZER; *\/ */
  /* /\* temp->ReaderCondition = PTHREAD_COND_INITIALIZER; *\/ */

  *rw=temp;

  if (rw->readers == 0 && rw->writers == 0)
    return 0;
  else
    return 1;
}

int
rw_destroy(struct rw_lock_t *rw)
{
  pthread_cond_destroy(&rw->WriterCondition);
  pthread_cond_destroy(&rw->ReaderCondition);
  pthread_mutex_destroy(&rw->WriterConditionMutex);
  pthread_mutex_destroy(&rw->WriterMutex);
  pthread_mutex_destroy(&rw->ReaderConditionMutex);
  free(rw);

  return 0;
}

int
rw_readlock(struct rw_lock_t *rw)
{
  if (rw->readers < 0) {
    printf("READER PANIC: %d\n", rw->readers);
    exit(2);
  }
  
  pthread_mutex_lock(&rw->WriterConditionMutex);
  while(rw->writers > 0) {
    pthread_cond_wait(&rw->WriterCondition, &rw->WriterConditionMutex);
  }
  pthread_mutex_unlock(&rw->WriterConditionMutex);

  pthread_mutex_lock(&rw->ReaderConditionMutex);
  rw->readers++;
  pthread_mutex_unlock(&rw->ReaderConditionMutex);

  return 0;
}

int
rw_readunlock(struct rw_lock_t *rw)
{
  if (rw->readers < 0) {
    printf("READER PANIC\n");
    exit(2);
  }

  pthread_mutex_lock(&rw->ReaderConditionMutex);
  rw->readers--;
  if (rw->readers == 0) {
    pthread_cond_broadcast(&rw->ReaderCondition);
  }
  pthread_mutex_unlock(&rw->ReaderConditionMutex);

  return 0;
}

int
rw_writelock(struct rw_lock_t *rw)
{
  pthread_mutex_lock(&rw->WriterConditionMutex);
  rw->writers++;

  if (rw->writers > 2) {
    printf("WRITER PANIC\n");
    exit(2);
  }
  pthread_mutex_unlock(&rw->WriterConditionMutex);
  
  pthread_mutex_lock(&rw->ReaderConditionMutex);
  while(rw->readers > 0) {
    pthread_cond_wait(&rw->ReaderCondition, &rw->ReaderConditionMutex);
  }
  pthread_mutex_unlock(&rw->ReaderConditionMutex);

  pthread_mutex_lock(&rw->WriterMutex);

  return 0;
}

int
rw_writeunlock(struct rw_lock_t *rw)
{
  pthread_mutex_lock(&rw->WriterConditionMutex);
  rw->writers--;
  pthread_mutex_unlock(&rw->WriterConditionMutex);
  
  pthread_mutex_lock(&rw->WriterConditionMutex);
  if (rw->writers == 0) {
    pthread_cond_broadcast(&rw->WriterCondition);
  }
  pthread_mutex_unlock(&rw->WriterConditionMutex);

  pthread_mutex_unlock(&rw->WriterMutex);

  return 0;
}