Changeset: 84f66ba47ea2 for MonetDB
URL: https://dev.monetdb.org/hg/MonetDB/rev/84f66ba47ea2
Modified Files:
gdk/gdk_bat.c
Branch: Dec2023
Log Message:
Delay calling BBPretain until after bat_iterator_end.
This fixes bug #7504.
diffs (53 lines):
diff --git a/gdk/gdk_bat.c b/gdk/gdk_bat.c
--- a/gdk/gdk_bat.c
+++ b/gdk/gdk_bat.c
@@ -2575,6 +2575,7 @@ BATmode(BAT *b, bool transient)
BATiter bi = bat_iterator(b);
bool mustrelease = false;
+ bool mustretain = false;
bat bid = b->batCacheid;
if (transient != bi.transient) {
@@ -2591,16 +2592,20 @@ BATmode(BAT *b, bool transient)
}
}
- /* persistent BATs get a logical reference */
+ /* we need to delay the calls to BBPretain and
+ * BBPrelease until after we have released our reference
+ * to the heaps (i.e. until after bat_iterator_end),
+ * because in either case, BBPfree can be called (either
+ * directly here or in BBPtrim) which waits for the heap
+ * reference to come down. BBPretain calls incref which
+ * waits until the trim that is waiting for us is done,
+ * so that causes deadlock, and BBPrelease can call
+ * BBPfree which causes deadlock with a single thread */
if (!transient) {
- BBPretain(bid);
+ /* persistent BATs get a logical reference */
+ mustretain = true;
} else if (!bi.transient) {
- /* we need to delay the release because if there
- * is no fix and the bat is loaded, BBPrelease
- * can call BBPfree which calls BATfree which
- * may hang while waiting for the heap reference
- * that we have because of the BAT iterator to
- * come down, in other words, deadlock */
+ /* transient BATs loose their logical reference */
mustrelease = true;
}
MT_lock_set(&GDKswapLock(bid));
@@ -2632,8 +2637,10 @@ BATmode(BAT *b, bool transient)
MT_lock_unset(&GDKswapLock(bid));
}
bat_iterator_end(&bi);
- /* release after bat_iterator_end because of refs to heaps */
- if (mustrelease)
+ /* retain/release after bat_iterator_end because of refs to heaps */
+ if (mustretain)
+ BBPretain(bid);
+ else if (mustrelease)
BBPrelease(bid);
return GDK_SUCCEED;
}
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