Fix dbcache/entry lock deadlock. If dbcache lock is held, it's

okay to read and write LDBM specific fields (state, refcnt,
LRU.  The id field, though is read-only once set.
cache_find_entry_dn2id(), hence, does not require any entry locks.
cache_find_entry_id() must do a entry_rdwr_trylock() and back
off if busy.
Add new rdwr lock code with trylock() functionality.
Implement entry_rdwr_trylock().

include/ldap_pvt_thread.h

@@ -180,6 +180,9 @@ LDAP_F int
 ldap_pvt_thread_set_concurrency LDAP_P(( int ));
 #endif
 
+#define LDAP_PVT_THREAD_CREATE_JOINABLE 0
+#define LDAP_PVT_THREAD_CREATE_DETACHED 1
+
 LDAP_F int 
 ldap_pvt_thread_create LDAP_P((
 	ldap_pvt_thread_t * thread, 
@@ -232,15 +235,17 @@ LDAP_F int
 ldap_pvt_thread_mutex_unlock LDAP_P(( ldap_pvt_thread_mutex_t *mutex ));
 
 typedef struct ldap_pvt_thread_rdwr_var {
-	int lt_readers_reading;
-	int lt_writer_writing;
-	ldap_pvt_thread_mutex_t lt_mutex;
-	ldap_pvt_thread_cond_t lt_lock_free;
+	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_VALUE 0x0bad
+	int ltrw_r_active;
+	int ltrw_w_active;
+	int ltrw_r_wait;
+	int ltrw_w_wait;
 } ldap_pvt_thread_rdwr_t;
 
-#define LDAP_PVT_THREAD_CREATE_DETACHED 1
-#define LDAP_PVT_THREAD_CREATE_JOINABLE 0
-
 LDAP_F int 
 ldap_pvt_thread_rdwr_init LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
@@ -248,21 +253,28 @@ ldap_pvt_thread_rdwr_destroy LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
 ldap_pvt_thread_rdwr_rlock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
+ldap_pvt_thread_rdwr_rtrylock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
+LDAP_F int 
 ldap_pvt_thread_rdwr_runlock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
 ldap_pvt_thread_rdwr_wlock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
+ldap_pvt_thread_rdwr_wtrylock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
+LDAP_F int 
 ldap_pvt_thread_rdwr_wunlock LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 
 #ifdef LDAP_DEBUG
 LDAP_F int 
-ldap_pvt_thread_rdwr_rchk LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
+ldap_pvt_thread_rdwr_readers LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
-ldap_pvt_thread_rdwr_wchk LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
+ldap_pvt_thread_rdwr_writers LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 LDAP_F int 
-ldap_pvt_thread_rdwr_rwchk LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
+ldap_pvt_thread_rdwr_active LDAP_P((ldap_pvt_thread_rdwr_t *rdwrp));
 #endif /* LDAP_DEBUG */
 
+#define LDAP_PVT_THREAD_EINVAL EINVAL
+#define LDAP_PVT_THREAD_EBUSY EINVAL
+
 LDAP_END_DECL
 
 #endif /* _LDAP_THREAD_H */

libraries/libldap_r/rdwr.c

 /*
-** 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.
- *
+ * Adapted from:
+ *	"Programming with Posix Threads"
+ *		by David R Butenhof
+ *		Addison-Wesley 
  ********************************************************
- * rdwr.c --
- * 
- * Library of functions implementing reader/writer locks
  */
 
 #include "portable.h"
 
 #include <stdlib.h>
 
+#include <ac/errno.h>
 #include "ldap_pvt_thread.h"
 
 int 
-ldap_pvt_thread_rdwr_init(ldap_pvt_thread_rdwr_t *rdwrp )
+ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rw )
 {
-	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) );
+	memset( rw, 0, sizeof(ldap_pvt_thread_rdwr_t) );
+
+	/* 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_VALUE;
 	return 0;
 }
 
 int 
-ldap_pvt_thread_rdwr_destroy(ldap_pvt_thread_rdwr_t *rdwrp )
+ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rw )
 {
-	ldap_pvt_thread_mutex_destroy(&(rdwrp->lt_mutex) );
-	ldap_pvt_thread_cond_destroy(&(rdwrp->lt_lock_free) );
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	/* active threads? */
+	if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 1) {
+		ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
+		return LDAP_PVT_THREAD_EBUSY;
+	}
+
+	/* 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_destroy( &rw->ltrw_mutex );
+	ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
+	ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
+
 	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_rlock( ldap_pvt_thread_rdwr_t *rw )
+{
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	if( rw->ltrw_w_active > 1 ) {
+		/* writer is active */
+
+		rw->ltrw_r_wait++;
+
+		do {
+			ldap_pvt_thread_cond_wait(
+				&rw->ltrw_read, &rw->ltrw_mutex );
+		} while( rw->ltrw_w_active > 1 );
+
+		rw->ltrw_r_wait--;
 	}
-	rdwrp->lt_readers_reading++;
-	ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
+
+	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 *rdwrp)
+int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
 {
-	ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
-	if (rdwrp->lt_readers_reading == 0) {
-		ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
-		return -1;
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	if( rw->ltrw_w_active > 1) {
+		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 *rw )
+{
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	rw->ltrw_r_active--;
+
+	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 *rw )
 {
-	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));
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	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--;
 	}
-	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 *rw )
 {
-	ldap_pvt_thread_mutex_lock(&(rdwrp->lt_mutex));
-	if (rdwrp->lt_writer_writing == 0) {
-		ldap_pvt_thread_mutex_unlock(&(rdwrp->lt_mutex));
-		return -1;
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	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 *rw )
+{
+	if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
+		return LDAP_PVT_THREAD_EINVAL;
+
+	ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
+
+	rw->ltrw_w_active--;
+
+	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
@@ -109,19 +206,20 @@ int ldap_pvt_thread_rdwr_wunlock(ldap_pvt_thread_rdwr_t *rdwrp)
  * 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 *rw)
 {
-	return(rdwrp->lt_readers_reading!=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 *rw)
 {
-	return(rdwrp->lt_writer_writing!=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 *rw)
 {
-	return(ldap_pvt_thread_rdwr_rchk(rdwrp) || 
-	       ldap_pvt_thread_rdwr_wchk(rdwrp));
+	return(ldap_pvt_thread_rdwr_readers(rw) +
+	       ldap_pvt_thread_rdwr_writers(rw));
 }
 
 #endif /* LDAP_DEBUG */

servers/slapd/back-ldbm/cache.c

@@ -4,6 +4,7 @@
 
 #include <stdio.h>
 
+#include <ac/errno.h>
 #include <ac/string.h>
 #include <ac/socket.h>
 
@@ -58,6 +59,7 @@ cache_set_state( struct cache *cache, Entry *e, int state )
 	ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
 }
 
+#ifdef not_used
 static void
 cache_return_entry( struct cache *cache, Entry *e )
 {
@@ -71,14 +73,25 @@ cache_return_entry( struct cache *cache, Entry *e )
 	/* free cache mutex */
 	ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
 }
+#endif
 
 static void
 cache_return_entry_rw( struct cache *cache, Entry *e, int rw )
 {
 	Debug( LDAP_DEBUG_TRACE, "====> cache_return_entry_%s\n",
 		rw ? "w" : "r", 0, 0);
+
+	/* set cache mutex */
+	ldap_pvt_thread_mutex_lock( &cache->c_mutex );
+
 	entry_rdwr_unlock(e, rw);;
-	cache_return_entry(cache, e);
+
+	if ( --e->e_refcnt == 0 && e->e_state == ENTRY_STATE_DELETED ) {
+		entry_free( e );
+	}
+
+	/* free cache mutex */
+	ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
 }
 
 void
@@ -202,7 +215,7 @@ cache_add_entry_lock(
 
 			/* XXX check for writer lock - should also check no readers pending */
 #ifdef LDAP_DEBUG
-			assert(!ldap_pvt_thread_rdwr_rwchk(&e->e_rdwr));
+			assert(!ldap_pvt_thread_rdwr_active( &e->e_rdwr ));
 #endif
 
 			/* delete from cache and lru q */
@@ -241,6 +254,11 @@ cache_find_entry_dn2id(
 	if ( (ep = (Entry *) avl_find( cache->c_dntree, (caddr_t) &e,
 		cache_entrydn_cmp )) != NULL )
 	{
+		/*
+		 * ep now points to an unlocked entry
+		 * we do not need to lock the entry if we only
+		 * check the state, refcnt, LRU, and id.
+		 */
 		free(e.e_ndn);
 
 		Debug(LDAP_DEBUG_TRACE, "====> cache_find_entry_dn2id: found dn: %s\n",
@@ -257,42 +275,16 @@ cache_find_entry_dn2id(
 			return( NOID );
 		}
 
-		/* XXX is this safe without writer lock? */
-		ep->e_refcnt++;
-
 		/* lru */
 		LRU_DELETE( cache, ep );
 		LRU_ADD( cache, ep );
-
-		/* acquire reader lock */
-		entry_rdwr_lock(ep, 0);
-
-		/* re-check */
-		if ( ep->e_state == ENTRY_STATE_DELETED ||
-			ep->e_state == ENTRY_STATE_CREATING )
-		{
-			/* XXX check that is is required */
-			ep->e_refcnt--;
-
-			/* free reader lock */
-			entry_rdwr_unlock(ep, 0);
-			/* free cache mutex */
-			ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
-
-			return( NOID );
-		}
-
+                
 		/* save id */
 		id = ep->e_id;
 
-		/* free reader lock */
-		entry_rdwr_unlock(ep, 0);
-
 		/* free cache mutex */
 		ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
 
-		cache_return_entry( &li->li_cache, ep );
-
 		return( id );
 	}
 
@@ -318,11 +310,12 @@ cache_find_entry_id(
 	Entry	e;
 	Entry	*ep;
 
+	e.e_id = id;
+
+try_again:
 	/* set cache mutex */
 	ldap_pvt_thread_mutex_lock( &cache->c_mutex );
 
-	e.e_id = id;
-
 	if ( (ep = (Entry *) avl_find( cache->c_idtree, (caddr_t) &e,
 		cache_entryid_cmp )) != NULL )
 	{
@@ -340,35 +333,25 @@ cache_find_entry_id(
 			ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
 			return( NULL );
 		}
-		/* XXX is this safe without writer lock? */
-		ep->e_refcnt++;
 
-		/* lru */
-		LRU_DELETE( cache, ep );
-		LRU_ADD( cache, ep );
-                
 		/* acquire reader lock */
-		entry_rdwr_lock(ep, 0);
-
-		/* re-check */
-		if ( ep->e_state == ENTRY_STATE_DELETED ||
-			ep->e_state == ENTRY_STATE_CREATING ) {
-
-			/* XXX check that is is required */
-			ep->e_refcnt--;
-
-			/* free reader lock */
-			entry_rdwr_unlock(ep, 0);
+		if ( entry_rdwr_trylock(ep, rw) == LDAP_PVT_THREAD_EBUSY ) {
+			/* could not acquire entry lock...
+			 * owner cannot free as we have the cache locked.
+			 * so, unlock the cache, yield, and try again.
+			 */
 
 			/* free cache mutex */
 			ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
-			return( NULL );
+			ldap_pvt_thread_yield();
+			goto try_again;
 		}
 
-		if ( rw ) {
-			entry_rdwr_unlock(ep, 0);
-			entry_rdwr_lock(ep, 1);
-		}
+		/* lru */
+		LRU_DELETE( cache, ep );
+		LRU_ADD( cache, ep );
+                
+		ep->e_refcnt++;
 
 		/* free cache mutex */
 		ldap_pvt_thread_mutex_unlock( &cache->c_mutex );
@@ -405,7 +388,7 @@ cache_delete_entry(
 
 	/* XXX check for writer lock - should also check no readers pending */
 #ifdef LDAP_DEBUG
-	assert(ldap_pvt_thread_rdwr_wchk(&e->e_rdwr));
+	assert(ldap_pvt_thread_rdwr_writers(&e->e_rdwr));
 #endif
 
 	/* set cache mutex */

servers/slapd/back-ldbm/id2entry.c

@@ -64,18 +64,13 @@ id2entry_delete( Backend *be, Entry *e )
 	Debug(LDAP_DEBUG_TRACE, "=> id2entry_delete( %lu, \"%s\" )\n", e->e_id,
 	    e->e_dn, 0 );
 
-	/* XXX - check for writer lock - should also check no reader pending */
 #ifdef LDAP_DEBUG
-	assert(ldap_pvt_thread_rdwr_wchk(&e->e_rdwr));
+	/* check for writer lock */
+	assert(ldap_pvt_thread_rdwr_writers(&e->e_rdwr) == 1);
 #endif
 
 	ldbm_datum_init( key );
 
-	/* XXX - check for writer lock - should also check no reader pending */
-	Debug (LDAP_DEBUG_TRACE,
-		"rdwr_Xchk: readers_reading: %d writer_writing: %d\n",
-		e->e_rdwr.lt_readers_reading, e->e_rdwr.lt_writer_writing, 0);
- 
 	if ( (db = ldbm_cache_open( be, "id2entry", LDBM_SUFFIX, LDBM_WRCREAT ))
 		== NULL ) {
 		Debug( LDAP_DEBUG_ANY, "Could not open/create id2entry%s\n",

servers/slapd/entry.c

@@ -5,6 +5,7 @@
 #include <stdio.h>
 
 #include <ac/ctype.h>
+#include <ac/errno.h>
 #include <ac/socket.h>
 #include <ac/string.h>
 
@@ -218,11 +219,20 @@ entry_free( Entry *e )
 	int		i;
 	Attribute	*a, *next;
 
-	/* XXX check that no reader/writer locks exist */
+	/* check that no reader/writer locks exist */
+
+	if ( ldap_pvt_thread_rdwr_wtrylock( &e->e_rdwr ) == 
+		LDAP_PVT_THREAD_EBUSY )
+	{
+		Debug( LDAP_DEBUG_ANY, "entry_free(%ld): active (%d, %d)\n",
+			e->e_id,
+			ldap_pvt_thread_rdwr_readers( &e->e_rdwr ),
+			ldap_pvt_thread_rdwr_writers( &e->e_rdwr ));
+
 #ifdef LDAP_DEBUG
-	assert( !ldap_pvt_thread_rdwr_wchk(&e->e_rdwr) &&
-		!ldap_pvt_thread_rdwr_rchk(&e->e_rdwr) );
+		assert(!ldap_pvt_thread_rdwr_active( &e->e_rdwr ));
 #endif
+	}
 
 	if ( e->e_dn != NULL ) {
 		free( e->e_dn );
@@ -260,6 +270,17 @@ entry_rdwr_wlock(Entry *e)
 	return entry_rdwr_lock( e, 1 );
 }
 
+int
+entry_rdwr_trylock(Entry *e, int rw)
+{
+	Debug( LDAP_DEBUG_ARGS, "entry_rdwr_%strylock: ID: %ld\n",
+		rw ? "w" : "r", e->e_id, 0);
+	if (rw)
+		return ldap_pvt_thread_rdwr_wtrylock(&e->e_rdwr);
+	else
+		return ldap_pvt_thread_rdwr_rtrylock(&e->e_rdwr);
+}
+
 int
 entry_rdwr_unlock(Entry *e, int rw)
 {