8215451: JNI IsSameObject should not keep objects alive

Reviewed-by: eosterlund, kbarrett

src/hotspot/share/prims/jni.cpp

@@ -823,9 +823,7 @@ JNI_QUICK_ENTRY(jboolean, jni_IsSameObject(JNIEnv *env, jobject r1, jobject r2))
 
   HOTSPOT_JNI_ISSAMEOBJECT_ENTRY(env, r1, r2);
 
-  oop a = JNIHandles::resolve(r1);
-  oop b = JNIHandles::resolve(r2);
-  jboolean ret = oopDesc::equals(a, b) ? JNI_TRUE : JNI_FALSE;
+  jboolean ret = JNIHandles::is_same_object(r1, r2) ? JNI_TRUE : JNI_FALSE;
 
   HOTSPOT_JNI_ISSAMEOBJECT_RETURN(ret);
   return ret;

src/hotspot/share/runtime/jniHandles.cpp

@@ -152,17 +152,11 @@ jobject JNIHandles::make_weak_global(Handle obj, AllocFailType alloc_failmode) {
 oop JNIHandles::resolve_external_guard(jobject handle) {
   oop result = NULL;
   if (handle != NULL) {
-    result = resolve_impl<true /* external_guard */ >(handle);
+    result = resolve_impl<0 /* decorators */, true /* external_guard */>(handle);
   }
   return result;
 }
 
-oop JNIHandles::resolve_jweak(jweak handle) {
-  assert(handle != NULL, "precondition");
-  assert(is_jweak(handle), "precondition");
-  return NativeAccess<ON_PHANTOM_OOP_REF>::oop_load(jweak_ptr(handle));
-}
-
 bool JNIHandles::is_global_weak_cleared(jweak handle) {
   assert(handle != NULL, "precondition");
   assert(is_jweak(handle), "not a weak handle");

src/hotspot/share/runtime/jniHandles.hpp

@@ -42,8 +42,10 @@ class JNIHandles : AllStatic {
   inline static oop* jobject_ptr(jobject handle); // NOT jweak!
   inline static oop* jweak_ptr(jobject handle);
 
-  template<bool external_guard> inline static oop resolve_impl(jobject handle);
-  static oop resolve_jweak(jweak handle);
+  template <DecoratorSet decorators, bool external_guard> inline static oop resolve_impl(jobject handle);
+
+  // Resolve handle into oop, without keeping the object alive
+  inline static oop resolve_no_keepalive(jobject handle);
 
   // This method is not inlined in order to avoid circular includes between
   // this header file and thread.hpp.
@@ -70,6 +72,9 @@ class JNIHandles : AllStatic {
   // Resolve externally provided handle into oop with some guards
   static oop resolve_external_guard(jobject handle);
 
+  // Check for equality without keeping objects alive
+  static bool is_same_object(jobject handle1, jobject handle2);
+
   // Local handles
   static jobject make_local(oop obj);
   static jobject make_local(JNIEnv* env, oop obj);    // Fast version when env is known

src/hotspot/share/runtime/jniHandles.inline.hpp

@@ -49,15 +49,15 @@ inline oop* JNIHandles::jweak_ptr(jobject handle) {
 }
 
 // external_guard is true if called from resolve_external_guard.
-template<bool external_guard>
+template <DecoratorSet decorators, bool external_guard>
 inline oop JNIHandles::resolve_impl(jobject handle) {
   assert(handle != NULL, "precondition");
   assert(!current_thread_in_native(), "must not be in native");
   oop result;
   if (is_jweak(handle)) {       // Unlikely
-    result = resolve_jweak(handle);
+    result = NativeAccess<ON_PHANTOM_OOP_REF|decorators>::oop_load(jweak_ptr(handle));
   } else {
-    result = NativeAccess<>::oop_load(jobject_ptr(handle));
+    result = NativeAccess<decorators>::oop_load(jobject_ptr(handle));
     // Construction of jobjects canonicalize a null value into a null
     // jobject, so for non-jweak the pointee should never be null.
     assert(external_guard || result != NULL, "Invalid JNI handle");
@@ -68,14 +68,28 @@ inline oop JNIHandles::resolve_impl(jobject handle) {
 inline oop JNIHandles::resolve(jobject handle) {
   oop result = NULL;
   if (handle != NULL) {
-    result = resolve_impl<false /* external_guard */ >(handle);
+    result = resolve_impl<0 /* decorators */, false /* external_guard */>(handle);
   }
   return result;
 }
 
+inline oop JNIHandles::resolve_no_keepalive(jobject handle) {
+  oop result = NULL;
+  if (handle != NULL) {
+    result = resolve_impl<AS_NO_KEEPALIVE, false /* external_guard */>(handle);
+  }
+  return result;
+}
+
+inline bool JNIHandles::is_same_object(jobject handle1, jobject handle2) {
+  oop obj1 = resolve_no_keepalive(handle1);
+  oop obj2 = resolve_no_keepalive(handle2);
+  return oopDesc::equals(obj1, obj2);
+}
+
 inline oop JNIHandles::resolve_non_null(jobject handle) {
   assert(handle != NULL, "JNI handle should not be null");
-  oop result = resolve_impl<false /* external_guard */ >(handle);
+  oop result = resolve_impl<0 /* decorators */, false /* external_guard */>(handle);
   assert(result != NULL, "NULL read from jni handle");
   return result;
 }

test/hotspot/jtreg/serviceability/jvmti/HeapMonitor/MyPackage/HeapMonitorThreadTest.java

@@ -30,7 +30,6 @@ package MyPackage;
  * @summary Verifies the JVMTI Heap Monitor Thread information sanity.
  * @compile HeapMonitorThreadTest.java
  * @run main/othervm/native -Xmx512m -agentlib:HeapMonitorTest MyPackage.HeapMonitorThreadTest
- * @requires !vm.gc.Z
  */
 
 import java.util.List;