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8298061: vmTestbase/nsk/sysdict/vm/stress/btree/btree012/btree012.java failed with "fatal error: refcount has gone to zero" #3328

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8298061: vmTestbase/nsk/sysdict/vm/stress/btree/btree012/btree012.java failed with "fatal error: refcount has gone to zero" #3328

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7 changes: 6 additions & 1 deletion src/hotspot/share/classfile/placeholders.cpp
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Original file line number Diff line number Diff line change
@@ -326,7 +326,12 @@ void PlaceholderTable::find_and_remove(unsigned int hash,
PlaceholderEntry *probe = get_entry(hash, name, loader_data);
if (probe != NULL) {
log(probe, "find_and_remove", action);
probe->remove_seen_thread(thread, action);

bool empty = probe->remove_seen_thread(thread, action);
if (empty && action == LOAD_SUPER) {
probe->set_supername(NULL);
}

// If no other threads using this entry, and this thread is not using this entry for other states
if ((probe->superThreadQ() == NULL) && (probe->loadInstanceThreadQ() == NULL)
&& (probe->defineThreadQ() == NULL) && (probe->definer() == NULL)) {
8 changes: 6 additions & 2 deletions src/hotspot/share/classfile/placeholders.hpp
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Original file line number Diff line number Diff line change
@@ -142,8 +142,12 @@ class PlaceholderEntry : public HashtableEntry<Symbol*, mtClass> {

Symbol* supername() const { return _supername; }
void set_supername(Symbol* supername) {
_supername = supername;
if (_supername != NULL) _supername->increment_refcount();
if (supername != _supername) {
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Why isn't there an if (_supername == NULL) _supername->decrement_refcount(); before assigning the new supername?

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Did you mean if (_supername != NULL)?
Later versions call Symbol::maybe_decrement_refcount(_supername); that acts like if (s != nullptr) s->decrement_refcount();.

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@dchuyko dchuyko Mar 24, 2025 •
edited
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Also it turns out that checking for NULL may be not enough. PlaceholderEntry has no constructor, so members can contain garbage.

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I see. This is the old hashtable implementation.

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Coleen, thanks for the review.

_supername = supername;
if (_supername != NULL) {
_supername->increment_refcount();
}
}
}

Thread* definer() const {return _definer; }