Added Reader/Writer lock code from publicily available examples for

Nichols, Butler, Farrell's book "Pthreads Programming" (O'Reilly).

diff --git a/libraries/liblthread/rdwr.c b/libraries/liblthread/rdwr.c
new file mode 100644 (file)
index 0000000..8de2be4
--- /dev/null
+++ b/libraries/liblthread/rdwr.c
@@ -0,0 +1,76 @@
+/********************************************************
+ * 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;
+       }
+}

diff --git a/libraries/liblthread/rdwr.h b/libraries/liblthread/rdwr.h
new file mode 100644 (file)
index 0000000..f4cda4d
--- /dev/null
+++ b/libraries/liblthread/rdwr.h
@@ -0,0 +1,28 @@
+/********************************************************
+ * 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);