8266642: improve ResolvedMethodTable hash function

Reviewed-by: vlivanov, coleenp

src/hotspot/share/classfile/classLoaderData.hpp

@@ -325,6 +325,10 @@ 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;)
 };
 

src/hotspot/share/prims/resolvedMethodTable.cpp

@@ -23,6 +23,7 @@
  */
 
 #include "precompiled.hpp"
+#include "classfile/classLoaderData.hpp"
 #include "classfile/javaClasses.hpp"
 #include "gc/shared/oopStorage.inline.hpp"
 #include "gc/shared/oopStorageSet.hpp"
@@ -53,7 +54,8 @@ static const size_t GROW_HINT = 32;
 static const size_t ResolvedMethodTableSizeLog = 10;
 
 unsigned int method_hash(const 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;

test/hotspot/jtreg/runtime/MemberName/ResolvedMethodTableHash.java

@@ -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) {
@@ -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");
             }