Commit 5d64c8f9 authored by Kurt Zeilenga's avatar Kurt Zeilenga
Browse files

Added Reader/Writer lock code from publicily available examples for

Nichols, Butler, Farrell's book "Pthreads Programming" (O'Reilly).
parent fe035ff1
/********************************************************
* 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;
}
}
/********************************************************
* An example source module to accompany...
*
* "Using POSIX Threads: Programming with Pthreads"
* by Brad nichols, Dick Buttlar, Jackie Farrell
* O'Reilly & Associates, Inc.
*
********************************************************
* rdwr.h --
*
* Include file for reader/writer locks
*/
typedef struct rdwr_var {
int readers_reading;
int writer_writing;
pthread_mutex_t mutex;
pthread_cond_t lock_free;
} pthread_rdwr_t;
typedef void * pthread_rdwrattr_t;
#define pthread_rdwrattr_default NULL;
int pthread_rdwr_init_np(pthread_rdwr_t *rdwrp, pthread_rdwrattr_t *attrp);
int pthread_rdwr_rlock_np(pthread_rdwr_t *rdwrp);
int pthread_rdwr_runlock_np(pthread_rdwr_t *rdwrp);
int pthread_rdwr_wlock_np(pthread_rdwr_t *rdwrp);
int pthread_rdwr_wunlock_np(pthread_rdwr_t *rdwrp);
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