1 /* 2 * Copyright (C) 2014 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "java_lang_ref_Reference.h" 18 19 #include "nativehelper/jni_macros.h" 20 21 #include "gc/heap.h" 22 #include "gc/reference_processor.h" 23 #include "jni/jni_internal.h" 24 #include "mirror/object-inl.h" 25 #include "mirror/reference-inl.h" 26 #include "native_util.h" 27 #include "scoped_fast_native_object_access-inl.h" 28 29 namespace art { 30 31 static jobject Reference_getReferent(JNIEnv* env, jobject javaThis) { 32 ScopedFastNativeObjectAccess soa(env); 33 const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis); 34 const ObjPtr<mirror::Object> referent = 35 Runtime::Current()->GetHeap()->GetReferenceProcessor()->GetReferent(soa.Self(), ref); 36 return soa.AddLocalReference<jobject>(referent); 37 } 38 39 static jboolean Reference_refersTo0(JNIEnv* env, jobject javaThis, jobject o) { 40 if (kUseReadBarrier && !kUseBakerReadBarrier) { 41 // Fall back to naive implementation that may block and needlessly preserve javaThis. 42 return env->IsSameObject(Reference_getReferent(env, javaThis), o); 43 } 44 ScopedFastNativeObjectAccess soa(env); 45 const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis); 46 const ObjPtr<mirror::Object> other = soa.Decode<mirror::Reference>(o); 47 const ObjPtr<mirror::Object> referent = ref->template GetReferent<kWithoutReadBarrier>(); 48 if (referent == other) { 49 return JNI_TRUE; 50 } 51 if (!kUseReadBarrier || referent.IsNull() || other.IsNull()) { 52 return JNI_FALSE; 53 } 54 // Explicitly handle the case in which referent is a from-space pointer. Don't use a 55 // read-barrier, since that could easily mark an object we no longer need and, since it 56 // creates new gray objects, may not be safe without blocking. 57 // 58 // ConcurrentCopying::Copy ensure that whenever a pointer to a to_space object is published, 59 // the forwarding pointer is also visible. We need that guarantee to ensure that if referent 60 // == other and referent is in from-space, then referent has a forwarding pointer. In order to 61 // use that guarantee, we need to ensure that the forwarding pointer is loaded after we 62 // retrieved other. Hence this fence: 63 atomic_thread_fence(std::memory_order_acquire); 64 // Note: On ARM, the above could be replaced by an asm fake-dependency hack to make 65 // referent appear to depend on other. That would be faster and uglier. 66 return gc::collector::ConcurrentCopying::GetFwdPtrUnchecked(referent.Ptr()) == other.Ptr() ? 67 JNI_TRUE : JNI_FALSE; 68 } 69 70 static void Reference_clearReferent(JNIEnv* env, jobject javaThis) { 71 ScopedFastNativeObjectAccess soa(env); 72 const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis); 73 Runtime::Current()->GetHeap()->GetReferenceProcessor()->ClearReferent(ref); 74 } 75 76 static JNINativeMethod gMethods[] = { 77 FAST_NATIVE_METHOD(Reference, getReferent, "()Ljava/lang/Object;"), 78 FAST_NATIVE_METHOD(Reference, clearReferent, "()V"), 79 FAST_NATIVE_METHOD(Reference, refersTo0, "(Ljava/lang/Object;)Z"), 80 }; 81 82 void register_java_lang_ref_Reference(JNIEnv* env) { 83 REGISTER_NATIVE_METHODS("java/lang/ref/Reference"); 84 } 85 86 } // namespace art 87