git.sur5r.net Git - openldap/blob - libraries/liblthread/rdwr.c

   1 /********************************************************
   2  * An example source module to accompany...
   3  *
   4  * "Using POSIX Threads: Programming with Pthreads"
   5  *               by Brad nichols, Dick Buttlar, Jackie Farrell
   6  *               O'Reilly & Associates, Inc.
   7  *
   8  ********************************************************
   9  * rdwr.c --
  10  *
  11  * Library of functions implementing reader/writer locks
  12  */
  13 #include <pthread.h>
  14 #include "rdwr.h"
  15
  16 int pthread_rdwr_init_np(pthread_rdwr_t *rdwrp, pthread_rdwrattr_t *attrp)
  17 {
  18         rdwrp->readers_reading = 0;
  19         rdwrp->writer_writing = 0;
  20         pthread_mutex_init(&(rdwrp->mutex), NULL);
  21         pthread_cond_init(&(rdwrp->lock_free), NULL);
  22         return 0;
  23 }
  24
  25 int pthread_rdwr_rlock_np(pthread_rdwr_t *rdwrp){
  26         pthread_mutex_lock(&(rdwrp->mutex));
  27         while(rdwrp->writer_writing) {
  28                 pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
  29         }
  30         rdwrp->readers_reading++;
  31         pthread_mutex_unlock(&(rdwrp->mutex));
  32         return 0;
  33 }
  34
  35 int pthread_rdwr_runlock_np(pthread_rdwr_t *rdwrp)
  36 {
  37         pthread_mutex_lock(&(rdwrp->mutex));
  38         if (rdwrp->readers_reading == 0) {
  39                 pthread_mutex_unlock(&(rdwrp->mutex));
  40                 return -1;
  41         }
  42         else {
  43                 rdwrp->readers_reading--;
  44                 if (rdwrp->readers_reading == 0) {
  45                         pthread_cond_signal(&(rdwrp->lock_free));
  46                 }
  47                 pthread_mutex_unlock(&(rdwrp->mutex));
  48                 return 0;
  49         }
  50 }
  51
  52 int pthread_rdwr_wlock_np(pthread_rdwr_t *rdwrp)
  53 {
  54         pthread_mutex_lock(&(rdwrp->mutex));
  55         while(rdwrp->writer_writing || rdwrp->readers_reading) {
  56                 pthread_cond_wait(&(rdwrp->lock_free), &(rdwrp->mutex));
  57         }
  58         rdwrp->writer_writing++;
  59         pthread_mutex_unlock(&(rdwrp->mutex));
  60         return 0;
  61 }
  62
  63 int pthread_rdwr_wunlock_np(pthread_rdwr_t *rdwrp)
  64 {
  65         pthread_mutex_lock(&(rdwrp->mutex));
  66         if (rdwrp->writer_writing == 0) {
  67                 pthread_mutex_unlock(&(rdwrp->mutex));
  68                 return -1;
  69         }
  70         else {
  71                 rdwrp->writer_writing = 0;
  72                 pthread_cond_broadcast(&(rdwrp->lock_free));
  73                 pthread_mutex_unlock(&(rdwrp->mutex));
  74                 return 0;
  75         }
  76 }