1 files changed, 78 insertions, 2 deletions

diff --git a/lib/isc/rwlock.c b/lib/isc/rwlock.c
index 6ddcbdba..c31b2a11 100644
--- a/lib/isc/rwlock.c
+++ b/lib/isc/rwlock.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 1998-2001  Internet Software Consortium.
+ * Copyright (C) 1998-2001, 2003  Internet Software Consortium.
  *
  * Permission to use, copy, modify, and distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
@@ -15,7 +15,7 @@
  * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
-/* $Id: rwlock.c,v 1.33 2001/04/17 14:36:45 tale Exp $ */
+/* $Id: rwlock.c,v 1.33.2.4 2003/07/23 03:20:24 marka Exp $ */
 
 #include <config.h>
 
@@ -82,6 +82,7 @@ isc_rwlock_init(isc_rwlock_t *rwl, unsigned int read_quota,
 	rwl->magic = 0;
 
 	rwl->type = isc_rwlocktype_read;
+	rwl->original = isc_rwlocktype_none;
 	rwl->active = 0;
 	rwl->granted = 0;
 	rwl->readers_waiting = 0;
@@ -206,6 +207,50 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 }
 
 isc_result_t
+isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
+	isc_result_t result = ISC_R_SUCCESS;
+
+	REQUIRE(VALID_RWLOCK(rwl));
+	LOCK(&rwl->lock);
+	REQUIRE(rwl->type == isc_rwlocktype_read);
+	REQUIRE(rwl->active != 0);
+
+	/* If we are the only reader then succeed. */
+	if (rwl->active == 1) {
+		rwl->original = (rwl->original == isc_rwlocktype_none) ?
+				isc_rwlocktype_read : isc_rwlocktype_none;
+		rwl->type = isc_rwlocktype_write;
+	} else
+		result = ISC_R_LOCKBUSY;
+
+	UNLOCK(&rwl->lock);
+	return (result);
+}
+
+void
+isc_rwlock_downgrade(isc_rwlock_t *rwl) {
+
+	REQUIRE(VALID_RWLOCK(rwl));
+	LOCK(&rwl->lock);
+	REQUIRE(rwl->type == isc_rwlocktype_write);
+	REQUIRE(rwl->active == 1);
+
+	rwl->type = isc_rwlocktype_read;
+	rwl->original = (rwl->original == isc_rwlocktype_none) ?
+			isc_rwlocktype_write : isc_rwlocktype_none;
+	/*
+	 * Resume processing any read request that were blocked when
+	 * we upgraded.
+	 */
+	if (rwl->original == isc_rwlocktype_none &&
+	    (rwl->writers_waiting == 0 || rwl->granted < rwl->read_quota) &&
+	    rwl->readers_waiting > 0)
+		BROADCAST(&rwl->readable);
+
+	UNLOCK(&rwl->lock);
+}
+
+isc_result_t
 isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 
 	REQUIRE(VALID_RWLOCK(rwl));
@@ -222,6 +267,10 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 	INSIST(rwl->active > 0);
 	rwl->active--;
 	if (rwl->active == 0) {
+		if (rwl->original != isc_rwlocktype_none) {
+			rwl->type = rwl->original;
+			rwl->original = isc_rwlocktype_none;
+		}
 		if (rwl->type == isc_rwlocktype_read) {
 			rwl->granted = 0;
 			if (rwl->writers_waiting > 0) {
@@ -249,6 +298,7 @@ isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 			}
 		}
 	}
+	INSIST(rwl->original == isc_rwlocktype_none);
 
 #ifdef ISC_RWLOCK_TRACE
 	print_lock(isc_msgcat_get(isc_msgcat, ISC_MSGSET_RWLOCK,
@@ -319,6 +369,32 @@ isc_rwlock_trylock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 }
 
 isc_result_t
+isc_rwlock_tryupgrade(isc_rwlock_t *rwl) {
+	isc_result_t result = ISC_R_SUCCESS;
+
+	REQUIRE(VALID_RWLOCK(rwl));
+	REQUIRE(rwl->type == isc_rwlocktype_read);
+	REQUIRE(rwl->active != 0);
+	
+	/* If we are the only reader then succeed. */
+	if (rwl->active == 1)
+		rwl->type = isc_rwlocktype_write;
+	else
+		result = ISC_R_LOCKBUSY;
+	return (result);
+}
+
+void
+isc_rwlock_downgrade(isc_rwlock_t *rwl) {
+
+	REQUIRE(VALID_RWLOCK(rwl));
+	REQUIRE(rwl->type == isc_rwlocktype_write);
+	REQUIRE(rwl->active == 1);
+
+	rwl->type = isc_rwlocktype_read;
+}
+
+isc_result_t
 isc_rwlock_unlock(isc_rwlock_t *rwl, isc_rwlocktype_t type) {
 	REQUIRE(VALID_RWLOCK(rwl));
 	REQUIRE(rwl->type == type);