blob: 4c411c8db437a0ffc20bee39ffb7613333d1acc0 [file] [log] [blame]
/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "java_lang_ref_Reference.h"
#include "nativehelper/jni_macros.h"
#include "gc/heap.h"
#include "gc/reference_processor.h"
#include "jni/jni_internal.h"
#include "mirror/object-inl.h"
#include "mirror/reference-inl.h"
#include "native_util.h"
#include "scoped_fast_native_object_access-inl.h"
namespace art HIDDEN {
static jobject Reference_getReferent(JNIEnv* env, jobject javaThis) {
ScopedFastNativeObjectAccess soa(env);
const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
const ObjPtr<mirror::Object> referent =
Runtime::Current()->GetHeap()->GetReferenceProcessor()->GetReferent(soa.Self(), ref);
return soa.AddLocalReference<jobject>(referent);
}
static jboolean Reference_refersTo0(JNIEnv* env, jobject javaThis, jobject o) {
if (gUseReadBarrier && !kUseBakerReadBarrier) {
// Fall back to naive implementation that may block and needlessly preserve javaThis.
return env->IsSameObject(Reference_getReferent(env, javaThis), o);
}
ScopedFastNativeObjectAccess soa(env);
const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
const ObjPtr<mirror::Object> other = soa.Decode<mirror::Reference>(o);
const ObjPtr<mirror::Object> referent = ref->template GetReferent<kWithoutReadBarrier>();
if (referent == other) {
return JNI_TRUE;
}
if (!gUseReadBarrier || referent.IsNull() || other.IsNull()) {
return JNI_FALSE;
}
// Explicitly handle the case in which referent is a from-space pointer. Don't use a
// read-barrier, since that could easily mark an object we no longer need and, since it creates
// new gray objects, may not be safe without blocking.
//
// Assume we're post flip in a GC. 'other' will always be a to-space reference. Thus the only
// remaining case in which we should return true is when 'referent' still points to from-space.
// ConcurrentCopying::Copy ensures that whenever a pointer to a to-space object is published,
// the forwarding pointer is also visible. Thus if 'other' and 'javaThis' refer to the same
// object, and we can ensure that the read of the forwarding pointer is ordered after the read
// of other, which ensured the forwarding pointer was set, then we're guaranteed to see the
// correct forwarding pointer, which should then match 'other'. This fence ensures that the
// forwarding pointer read is ordered with respect to the access to 'other':
atomic_thread_fence(std::memory_order_acquire);
// Note: On ARM and RISC-V, the above could be replaced by an asm fake-dependency hack to make
// referent appear to depend on other. That would be faster and uglier.
return gc::collector::ConcurrentCopying::GetFwdPtrUnchecked(referent.Ptr()) == other.Ptr() ?
JNI_TRUE : JNI_FALSE;
}
static void Reference_clearReferent(JNIEnv* env, jobject javaThis) {
ScopedFastNativeObjectAccess soa(env);
const ObjPtr<mirror::Reference> ref = soa.Decode<mirror::Reference>(javaThis);
Runtime::Current()->GetHeap()->GetReferenceProcessor()->ClearReferent(ref);
}
static JNINativeMethod gMethods[] = {
FAST_NATIVE_METHOD(Reference, getReferent, "()Ljava/lang/Object;"),
FAST_NATIVE_METHOD(Reference, clearReferent, "()V"),
FAST_NATIVE_METHOD(Reference, refersTo0, "(Ljava/lang/Object;)Z"),
};
void register_java_lang_ref_Reference(JNIEnv* env) {
REGISTER_NATIVE_METHODS("java/lang/ref/Reference");
}
} // namespace art