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8383567: [lworld] VM.class_print_layout should use external class names #2375

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8383567: [lworld] VM.class_print_layout should use external class names #2375

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2bdaa63
change print_class_layout to use external class names
caspernorrbin Apr 29, 2026
c8df796
feedback fixes
caspernorrbin Apr 30, 2026
eb127d3
feedback
caspernorrbin May 4, 2026
6baa184
Merge branch 'lworld' into print_class_layout_external_names
caspernorrbin May 12, 2026
7a18def
indent fix
caspernorrbin May 12, 2026
d1ffe8a
merge miss
caspernorrbin May 12, 2026
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20 changes: 8 additions & 12 deletions src/hotspot/share/memory/heapInspection.cpp
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2002, 2025, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2002, 2026, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
Expand Down Expand Up @@ -513,16 +513,16 @@ class HistoClosure : public KlassInfoClosure {
}
};

class FindClassByNameClosure : public KlassInfoClosure {
class FindClassByExternalNameClosure : public KlassInfoClosure {
private:
GrowableArray<Klass*>* _klasses;
Symbol* _classname;
const char* _classname;
public:
FindClassByNameClosure(GrowableArray<Klass*>* klasses, Symbol* classname) :
FindClassByExternalNameClosure(GrowableArray<Klass*>* klasses, const char* classname) :
_klasses(klasses), _classname(classname) { }

void do_cinfo(KlassInfoEntry* cie) {
if (cie->klass()->name() == _classname) {
if (strcmp(cie->klass()->external_name(), _classname) == 0) {
_klasses->append(cie->klass());
}
}
Expand Down Expand Up @@ -600,23 +600,19 @@ void PrintClassLayout::print_class_layout(outputStream* st, char* class_name) {
return;
}

Thread* THREAD = Thread::current();

Symbol* classname = SymbolTable::probe(class_name, (int)strlen(class_name));

GrowableArray<Klass*>* klasses = new (mtServiceability) GrowableArray<Klass*>(100, mtServiceability);

FindClassByNameClosure fbnc(klasses, classname);
ResourceMark rm;
FindClassByExternalNameClosure fbnc(klasses, class_name);
cit.iterate(&fbnc);

for(int i = 0; i < klasses->length(); i++) {
Klass* klass = klasses->at(i);
if (!klass->is_instance_klass()) continue; // Skip
InstanceKlass* ik = InstanceKlass::cast(klass);
int tab = 1;
st->print_cr("Class %s [@%s]:", klass->name()->as_C_string(),
st->print_cr("Class %s [@%s]:", klass->external_name(),
Comment on lines -611 to +617
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@dholmes-ora dholmes-ora Apr 30, 2026

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Doesn't it suffice to just make this change? If we convert to Symbol it seems more efficient than using strcmp (though I confess I'm not clear what this closure is actually doing and what set of classes it potentially generates).

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@caspernorrbin caspernorrbin Apr 30, 2026

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I agree using strcmp is not very efficient, since we iterate the full KlassInfoTable. We still need to keep the external name as the argument however, but I reverted most changes for a different design. Now, we instead convert user input from dotted to slash form once, then use the same logic as before (probe the symbol table, then match on klass->name()). That way, we don't have to worry about comparing strings and we avoid lots of allocations from external_name()

As a side effect, this now also works on both internal and external names, as slashes would be left untouched.

klass->class_loader_data()->loader_name());
ResourceMark rm;
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@dholmes-ora dholmes-ora Apr 30, 2026

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You may still need this to limit the ResourceArea usage, otherwise you will be keeping all allocations from the complete loop alive.

GrowableArray<FieldDesc>* fields = new (mtServiceability) GrowableArray<FieldDesc>(100, mtServiceability);
for (AllFieldStream fd(ik); !fd.done(); fd.next()) {
if (!fd.access_flags().is_static()) {
Expand Down
8 changes: 4 additions & 4 deletions test/hotspot/jtreg/runtime/valhalla/inlinetypes/ClassPrintLayoutDcmd.java
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Expand Up @@ -81,10 +81,10 @@ static void testCmd(String arg, int expectExitCode, String... expectStrings) thr
}

public static void main(String args[]) throws Exception {
testCmd("foo/bar", 0, "");
testCmd("foo.bar", 0, "");
testCmd("", 1, "IllegalArgumentException", "mandatory");
testCmd("java/lang/Object", 0, "java/lang/Object", "@bootstrap");
testCmd("java/lang/Class", 0, "java/lang/Class", "@bootstrap");
testCmd("runtime/valhalla/inlinetypes/ClassPrintLayoutDcmd$Line", 0, "@app", "p1", "p2");
testCmd("java.lang.Object", 0, "java.lang.Object", "@bootstrap");
testCmd("java.lang.Class", 0, "java.lang.Class", "@bootstrap");
testCmd("runtime.valhalla.inlinetypes.ClassPrintLayoutDcmd$Line", 0, "@app", "p1", "p2");
}
}