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8266642: Improve ResolvedMethodTable hash function #12

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8266642: Improve ResolvedMethodTable hash function #12

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4 changes: 4 additions & 0 deletions src/hotspot/share/classfile/classLoaderData.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -419,6 +419,10 @@ class ClassLoaderData : public CHeapObj<mtClass> {
const char* loader_name_and_id() const;
Symbol* name_and_id() const { return _name_and_id; }

unsigned identity_hash() const {
return (unsigned)((uintptr_t)this >> 3);
}

JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
};

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4 changes: 3 additions & 1 deletion src/hotspot/share/prims/resolvedMethodTable.cpp
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Expand Up @@ -23,6 +23,7 @@
*/

#include "precompiled.hpp"
#include "classfile/classLoaderData.hpp"
#include "classfile/javaClasses.hpp"
#include "logging/log.hpp"
#include "memory/allocation.hpp"
Expand Down Expand Up @@ -78,7 +79,8 @@ oop ResolvedMethodTable::lookup(int index, unsigned int hash, Method* method) {
}

unsigned int ResolvedMethodTable::compute_hash(Method* method) {
unsigned int hash = method->klass_name()->identity_hash();
unsigned int hash = method->method_holder()->class_loader_data()->identity_hash();
hash = (hash * 31) ^ method->klass_name()->identity_hash();
hash = (hash * 31) ^ method->name()->identity_hash();
hash = (hash * 31) ^ method->signature()->identity_hash();
return hash;
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15 changes: 14 additions & 1 deletion test/hotspot/jtreg/runtime/MemberName/ResolvedMethodTableHash.java
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Expand Up @@ -48,6 +48,14 @@ private MethodHandle generate(String className) throws ReflectiveOperationExcept
return MethodHandles.publicLookup().findStatic(cls, "m", MethodType.methodType(void.class));
}

private MethodHandle generateWithSameName() throws ReflectiveOperationException {
byte[] buf = new byte[100];
int size = writeClass(buf, "MH$$");
// use different classloader instances to load the classes with the same name
Class<?> cls = new ResolvedMethodTableHash().defineClass(null, buf, 0, size);
return MethodHandles.publicLookup().findStatic(cls, "m", MethodType.methodType(void.class));
}

// Produce a class file with the given name and a single method:
// public static native void m();
private int writeClass(byte[] buf, String className) {
Expand Down Expand Up @@ -82,7 +90,12 @@ public static void main(String[] args) throws Exception {
int count = args.length > 0 ? Integer.parseInt(args[0]) : 200000;

for (int i = 0; i < count; i++) {
handles.add(generator.generate("MH$" + i));
// prevents metaspace oom
if (i % 20 != 0) {
handles.add(generator.generate("MH$" + i));
} else {
handles.add(generator.generateWithSameName());
}
if (i % 1000 == 0) {
System.out.println("Generated " + i + " handles");
}
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