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-rw-r--r--db2/lock/lock.c90
1 files changed, 58 insertions, 32 deletions
diff --git a/db2/lock/lock.c b/db2/lock/lock.c
index f1223a9..9b1cbc8 100644
--- a/db2/lock/lock.c
+++ b/db2/lock/lock.c
@@ -8,7 +8,7 @@
#include "config.h"
#ifndef lint
-static const char sccsid[] = "@(#)lock.c 10.38 (Sleepycat) 10/25/97";
+static const char sccsid[] = "@(#)lock.c 10.41 (Sleepycat) 11/28/97";
#endif /* not lint */
#ifndef NO_SYSTEM_INCLUDES
@@ -91,7 +91,7 @@ __lock_create(path, mode, dbenv)
if ((ret =
__db_rcreate(dbenv, DB_APP_NONE, path, DB_DEFAULT_LOCK_FILE, mode,
LOCK_REGION_SIZE(lock_modes, maxlocks, __db_tablesize(maxlocks)),
- &fd, &lrp)) != 0)
+ 0, &fd, &lrp)) != 0)
return (ret);
/* Region exists; now initialize it. */
@@ -600,7 +600,9 @@ __lock_put_internal(lt, lockp, do_all)
if (SH_TAILQ_FIRST(&sh_obj->holders, __db_lock) == NULL) {
HASHREMOVE_EL(lt->hashtab, __db_lockobj,
links, sh_obj, lt->region->table_size, __lock_lhash);
- __db_shalloc_free(lt->mem, SH_DBT_PTR(&sh_obj->lockobj));
+ if (sh_obj->lockobj.size > sizeof(sh_obj->objdata))
+ __db_shalloc_free(lt->mem,
+ SH_DBT_PTR(&sh_obj->lockobj));
SH_TAILQ_INSERT_HEAD(&lt->region->free_objs, sh_obj, links,
__db_lockobj);
state_changed = 1;
@@ -633,7 +635,7 @@ __lock_get_internal(lt, locker, flags, obj, lock_mode, lockp)
DB_LOCKOBJ *sh_obj, *sh_locker;
DB_LOCKREGION *lrp;
size_t newl_off;
- int ret;
+ int ihold, ret;
ret = 0;
/*
@@ -680,29 +682,40 @@ __lock_get_internal(lt, locker, flags, obj, lock_mode, lockp)
* new lock if it does not conflict with anyone on the holders list
* OR anyone on the waiters list. The reason that we don't grant if
* there's a conflict is that this can lead to starvation (a writer
- * waiting on a popularly read item will never ben granted). The
+ * waiting on a popularly read item will never be granted). The
* downside of this is that a waiting reader can prevent an upgrade
- * from reader to writer, which is not uncommon. In case of conflict,
- * we put the new lock on the end of the waiters list.
+ * from reader to writer, which is not uncommon.
+ *
+ * There is one exception to the no-conflict rule. If a lock is held
+ * by the requesting locker AND the new lock does not conflict with
+ * any other holders, then we grant the lock. The most common place
+ * this happens is when the holder has a WRITE lock and a READ lock
+ * request comes in for the same locker. If we do not grant the read
+ * lock, then we guarantee deadlock.
+ *
+ * In case of conflict, we put the new lock on the end of the waiters
+ * list.
*/
+ ihold = 0;
for (lp = SH_TAILQ_FIRST(&sh_obj->holders, __db_lock);
lp != NULL;
lp = SH_TAILQ_NEXT(lp, links, __db_lock)) {
- if (CONFLICTS(lt, lp->mode, lock_mode) &&
- locker != lp->holder)
+ if (locker == lp->holder) {
+ if (lp->mode == lock_mode &&
+ lp->status == DB_LSTAT_HELD) {
+ /* Lock is held, just inc the ref count. */
+ lp->refcount++;
+ SH_TAILQ_INSERT_HEAD(&lrp->free_locks,
+ newl, links, __db_lock);
+ *lockp = lp;
+ return (0);
+ } else
+ ihold = 1;
+ } else if (CONFLICTS(lt, lp->mode, lock_mode))
break;
- else if (lp->holder == locker && lp->mode == lock_mode &&
- lp->status == DB_LSTAT_HELD) {
- /* Lock is already held, just inc the ref count. */
- lp->refcount++;
- SH_TAILQ_INSERT_HEAD(&lrp->free_locks, newl, links,
- __db_lock);
- *lockp = lp;
- return (0);
- }
}
- if (lp == NULL)
+ if (lp == NULL && !ihold)
for (lp = SH_TAILQ_FIRST(&sh_obj->waiters, __db_lock);
lp != NULL;
lp = SH_TAILQ_NEXT(lp, links, __db_lock)) {
@@ -1261,25 +1274,37 @@ __lock_getobj(lt, locker, dbt, type, objp)
*/
if (sh_obj == NULL) {
/* Create new object and then insert it into hash table. */
- if ((sh_obj = SH_TAILQ_FIRST(&lrp->free_objs, __db_lockobj))
- == NULL) {
+ if ((sh_obj =
+ SH_TAILQ_FIRST(&lrp->free_objs, __db_lockobj)) == NULL) {
if ((ret = __lock_grow_region(lt, DB_LOCK_OBJ, 0)) != 0)
return (ret);
lrp = lt->region;
sh_obj = SH_TAILQ_FIRST(&lrp->free_objs, __db_lockobj);
}
- if ((ret = __db_shalloc(lt->mem, obj_size, 0, &p)) != 0) {
- if ((ret = __lock_grow_region(lt,
- DB_LOCK_MEM, obj_size)) != 0)
- return (ret);
- lrp = lt->region;
- /* Reacquire the head of the list. */
- sh_obj = SH_TAILQ_FIRST(&lrp->free_objs, __db_lockobj);
- (void)__db_shalloc(lt->mem, obj_size, 0, &p);
- }
- sh_obj->type = type;
+
+ /*
+ * If we can fit this object in the structure, do so instead
+ * of shalloc-ing space for it.
+ */
+ if (obj_size <= sizeof(sh_obj->objdata))
+ p = sh_obj->objdata;
+ else
+ if ((ret =
+ __db_shalloc(lt->mem, obj_size, 0, &p)) != 0) {
+ if ((ret = __lock_grow_region(lt,
+ DB_LOCK_MEM, obj_size)) != 0)
+ return (ret);
+ lrp = lt->region;
+ /* Reacquire the head of the list. */
+ sh_obj = SH_TAILQ_FIRST(&lrp->free_objs,
+ __db_lockobj);
+ (void)__db_shalloc(lt->mem, obj_size, 0, &p);
+ }
+
src = type == DB_LOCK_OBJTYPE ? dbt->data : (void *)&locker;
memcpy(p, src, obj_size);
+
+ sh_obj->type = type;
SH_TAILQ_REMOVE(&lrp->free_objs, sh_obj, links, __db_lockobj);
SH_TAILQ_INIT(&sh_obj->waiters);
@@ -1329,7 +1354,8 @@ __lock_freeobj(lt, obj)
{
HASHREMOVE_EL(lt->hashtab,
__db_lockobj, links, obj, lt->region->table_size, __lock_lhash);
- __db_shalloc_free(lt->mem, SH_DBT_PTR(&obj->lockobj));
+ if (obj->lockobj.size > sizeof(obj->objdata))
+ __db_shalloc_free(lt->mem, SH_DBT_PTR(&obj->lockobj));
SH_TAILQ_INSERT_HEAD(&lt->region->free_objs, obj, links, __db_lockobj);
}
generated by cgit v1.1 at 2024-12-15 16:06:09 +0000