+/* $OpenLDAP$ */
/*
-** This basic implementation of Reader/Writer locks does not
-** protect writers from starvation. That is, if a writer is
+** This is an improved implementation of Reader/Writer locks does
+** not protect writers from starvation. That is, if a writer is
** currently waiting on a reader, any new reader will get
** the lock before the writer.
+**
+** Does not support cancellation nor does any status checking.
*/
-
-/********************************************************
- * 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
+/* Adapted from publically available examples for:
+ * "Programming with Posix Threads"
+ * by David R Butenhof, Addison-Wesley
+ * http://cseng.aw.com/bookpage.taf?ISBN=0-201-63392-2
*/
#include "portable.h"
-#include <stdlib.h>
+#include <ac/stdlib.h>
+#include <ac/errno.h>
+#include <ac/string.h>
+#include <ac/time.h>
+
+#include "ldap-int.h"
#include "ldap_pvt_thread.h"
+/*
+ * implementations that provide their own compatible
+ * reader/writer locks define LDAP_THREAD_HAVE_RDWR
+ * in ldap_pvt_thread.h
+ */
+#ifndef LDAP_THREAD_HAVE_RDWR
+
+struct ldap_int_thread_rdwr_s {
+ ldap_pvt_thread_mutex_t ltrw_mutex;
+ ldap_pvt_thread_cond_t ltrw_read; /* wait for read */
+ ldap_pvt_thread_cond_t ltrw_write; /* wait for write */
+ int ltrw_valid;
+#define LDAP_PVT_THREAD_RDWR_VALID 0x0bad
+ int ltrw_r_active;
+ int ltrw_w_active;
+ int ltrw_r_wait;
+ int ltrw_w_wait;
+};
+
int
-ldap_pvt_thread_rdwr_init(ldap_pvt_thread_rdwr_t *rdwrp )
+ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rwlock )
{
- rdwrp->lt_readers_reading = 0;
- rdwrp->lt_writer_writing = 0;
- ldap_pvt_thread_mutex_init(&(rdwrp->lt_mutex) );
- ldap_pvt_thread_cond_init(&(rdwrp->lt_lock_free) );
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+
+ rw = (struct ldap_int_thread_rdwr_s *) LDAP_CALLOC( 1,
+ sizeof( struct ldap_int_thread_rdwr_s ) );
+
+ /* we should check return results */
+ ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
+ ldap_pvt_thread_cond_init( &rw->ltrw_read );
+ ldap_pvt_thread_cond_init( &rw->ltrw_write );
+
+ rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
+
+ *rwlock = rw;
return 0;
}
-int ldap_pvt_thread_rdwr_rlock(ldap_pvt_thread_rdwr_t *rdwrp){
- ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
- while(rdwrp->lt_writer_writing) {
- ldap_pvt_thread_cond_wait(&(rdwrp->lt_lock_free),
- &(rdwrp->lt_mutex));
+int
+ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
+{
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ /* active threads? */
+ if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+ return LDAP_PVT_THREAD_EBUSY;
}
- rdwrp->lt_readers_reading++;
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
+
+ /* waiting threads? */
+ if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+ return LDAP_PVT_THREAD_EBUSY;
+ }
+
+ rw->ltrw_valid = 0;
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
+ ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
+ ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
+
+ LDAP_FREE(rw);
+ *rwlock = NULL;
return 0;
}
-int ldap_pvt_thread_rdwr_runlock(ldap_pvt_thread_rdwr_t *rdwrp)
+int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
{
- ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
- if (rdwrp->lt_readers_reading == 0) {
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
- return -1;
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if( rw->ltrw_w_active > 0 ) {
+ /* writer is active */
+
+ rw->ltrw_r_wait++;
+
+ do {
+ ldap_pvt_thread_cond_wait(
+ &rw->ltrw_read, &rw->ltrw_mutex );
+ } while( rw->ltrw_w_active > 0 );
+
+ rw->ltrw_r_wait--;
+ assert( rw->ltrw_r_wait >= 0 );
+ }
+
+ rw->ltrw_r_active++;
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ return 0;
+}
+
+int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
+{
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if( rw->ltrw_w_active > 0) {
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+ return LDAP_PVT_THREAD_EBUSY;
}
- else {
- rdwrp->lt_readers_reading--;
- if (rdwrp->lt_readers_reading == 0) {
- ldap_pvt_thread_cond_signal(&(rdwrp->lt_lock_free));
- }
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
- return 0;
+
+ rw->ltrw_r_active++;
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ return 0;
+}
+
+int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
+{
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ rw->ltrw_r_active--;
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
+ ldap_pvt_thread_cond_signal( &rw->ltrw_write );
}
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ return 0;
}
-int ldap_pvt_thread_rdwr_wlock(ldap_pvt_thread_rdwr_t *rdwrp)
+int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
{
- ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
- while(rdwrp->lt_writer_writing || rdwrp->lt_readers_reading) {
- ldap_pvt_thread_cond_wait(&(rdwrp->lt_lock_free),
- &(rdwrp->lt_mutex));
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
+ rw->ltrw_w_wait++;
+
+ do {
+ ldap_pvt_thread_cond_wait(
+ &rw->ltrw_write, &rw->ltrw_mutex );
+ } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
+
+ rw->ltrw_w_wait--;
+ assert( rw->ltrw_w_wait >= 0 );
}
- rdwrp->lt_writer_writing++;
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
+
+ rw->ltrw_w_active++;
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
return 0;
}
-int ldap_pvt_thread_rdwr_wunlock(ldap_pvt_thread_rdwr_t *rdwrp)
+int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rwlock )
{
- ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
- if (rdwrp->lt_writer_writing == 0) {
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
- return -1;
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+ return LDAP_PVT_THREAD_EBUSY;
}
- else {
- rdwrp->lt_writer_writing = 0;
- ldap_pvt_thread_cond_broadcast(&(rdwrp->lt_lock_free));
- ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
- return 0;
+
+ rw->ltrw_w_active++;
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ return 0;
+}
+
+int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
+{
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+
+ if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
+ return LDAP_PVT_THREAD_EINVAL;
+
+ ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+ rw->ltrw_w_active--;
+
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ if (rw->ltrw_r_wait > 0) {
+ ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
+
+ } else if (rw->ltrw_w_wait > 0) {
+ ldap_pvt_thread_cond_signal( &rw->ltrw_write );
}
+
+ ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+
+ return 0;
}
-#ifdef LDAP_DEBUG
+#ifdef LDAP_RDWR_DEBUG
/* just for testing,
* return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
* a lock are caught.
*/
-int ldap_pvt_thread_rdwr_rchk(ldap_pvt_thread_rdwr_t *rdwrp)
+int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
{
- return(rdwrp->lt_readers_reading!=0);
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ return( rw->ltrw_r_active );
}
-int ldap_pvt_thread_rdwr_wchk(ldap_pvt_thread_rdwr_t *rdwrp)
+int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
{
- return(rdwrp->lt_writer_writing!=0);
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ return( rw->ltrw_w_active );
}
-int ldap_pvt_thread_rdwr_rwchk(ldap_pvt_thread_rdwr_t *rdwrp)
+
+int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
{
- return(ldap_pvt_thread_rdwr_rchk(rdwrp) ||
- ldap_pvt_thread_rdwr_wchk(rdwrp));
+ struct ldap_int_thread_rdwr_s *rw;
+
+ assert( rwlock != NULL );
+ rw = *rwlock;
+
+ assert( rw != NULL );
+ assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
+ assert( rw->ltrw_w_active >= 0 );
+ assert( rw->ltrw_w_wait >= 0 );
+ assert( rw->ltrw_r_active >= 0 );
+ assert( rw->ltrw_r_wait >= 0 );
+
+ return(ldap_pvt_thread_rdwr_readers(rw) +
+ ldap_pvt_thread_rdwr_writers(rw));
}
#endif /* LDAP_DEBUG */
+
+#endif /* LDAP_THREAD_HAVE_RDWR */
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