runtime/gc/reference_processor.cc - platform/art - Git at Google

 /*
  * 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 "reference_processor.h"

 #include "mirror/object-inl.h"
 #include "mirror/reference.h"
 #include "mirror/reference-inl.h"
 #include "reference_processor-inl.h"
 #include "reflection.h"
 #include "ScopedLocalRef.h"
 #include "scoped_thread_state_change.h"
 #include "well_known_classes.h"

 namespace art {
 namespace gc {

 ReferenceProcessor::ReferenceProcessor()
     : process_references_args_(nullptr, nullptr, nullptr),
       preserving_references_(false), lock_("reference processor lock", kReferenceProcessorLock),
       condition_("reference processor condition", lock_) {
 }

 void ReferenceProcessor::EnableSlowPath() {
   mirror::Reference::GetJavaLangRefReference()->SetSlowPath(true);
 }

 void ReferenceProcessor::DisableSlowPath(Thread* self) {
   mirror::Reference::GetJavaLangRefReference()->SetSlowPath(false);
   condition_.Broadcast(self);
 }

 mirror::Object* ReferenceProcessor::GetReferent(Thread* self, mirror::Reference* reference) {
   mirror::Object* const referent = reference->GetReferent();
   // If the referent is null then it is already cleared, we can just return null since there is no
   // scenario where it becomes non-null during the reference processing phase.
   if (UNLIKELY(!SlowPathEnabled()) || referent == nullptr) {
     return referent;
   }
   MutexLock mu(self, lock_);
   while (SlowPathEnabled()) {
     mirror::HeapReference<mirror::Object>* const referent_addr =
         reference->GetReferentReferenceAddr();
     // If the referent became cleared, return it. Don't need barrier since thread roots can't get
     // updated until after we leave the function due to holding the mutator lock.
     if (referent_addr->AsMirrorPtr() == nullptr) {
       return nullptr;
     }
     // Try to see if the referent is already marked by using the is_marked_callback. We can return
     // it to the mutator as long as the GC is not preserving references.
     IsHeapReferenceMarkedCallback* const is_marked_callback =
         process_references_args_.is_marked_callback_;
     if (LIKELY(is_marked_callback != nullptr)) {
       // If it's null it means not marked, but it could become marked if the referent is reachable
       // by finalizer referents. So we can not return in this case and must block. Otherwise, we
       // can return it to the mutator as long as the GC is not preserving references, in which
       // case only black nodes can be safely returned. If the GC is preserving references, the
       // mutator could take a white field from a grey or white node and move it somewhere else
       // in the heap causing corruption since this field would get swept.
       if (is_marked_callback(referent_addr, process_references_args_.arg_)) {
         if (!preserving_references_ ||
            (LIKELY(!reference->IsFinalizerReferenceInstance()) && !reference->IsEnqueued())) {
           return referent_addr->AsMirrorPtr();
         }
       }
     }
     condition_.WaitHoldingLocks(self);
   }
   return reference->GetReferent();
 }

 bool ReferenceProcessor::PreserveSoftReferenceCallback(mirror::HeapReference<mirror::Object>* obj,
                                                        void* arg) {
   auto* const args = reinterpret_cast<ProcessReferencesArgs*>(arg);
   // TODO: Add smarter logic for preserving soft references.
   mirror::Object* new_obj = args->mark_callback_(obj->AsMirrorPtr(), args->arg_);
   DCHECK(new_obj != nullptr);
   obj->Assign(new_obj);
   return true;
 }

 void ReferenceProcessor::StartPreservingReferences(Thread* self) {
   MutexLock mu(self, lock_);
   preserving_references_ = true;
 }

 void ReferenceProcessor::StopPreservingReferences(Thread* self) {
   MutexLock mu(self, lock_);
   preserving_references_ = false;
   // We are done preserving references, some people who are blocked may see a marked referent.
   condition_.Broadcast(self);
 }

 // Process reference class instances and schedule finalizations.
 void ReferenceProcessor::ProcessReferences(bool concurrent, TimingLogger* timings,
                                            bool clear_soft_references,
                                            IsHeapReferenceMarkedCallback* is_marked_callback,
                                            MarkObjectCallback* mark_object_callback,
                                            ProcessMarkStackCallback* process_mark_stack_callback,
                                            void* arg) {
   TimingLogger::ScopedTiming t(concurrent ? __FUNCTION__ : "(Paused)ProcessReferences", timings);
   Thread* self = Thread::Current();
   {
     MutexLock mu(self, lock_);
     process_references_args_.is_marked_callback_ = is_marked_callback;
     process_references_args_.mark_callback_ = mark_object_callback;
     process_references_args_.arg_ = arg;
     CHECK_EQ(SlowPathEnabled(), concurrent) << "Slow path must be enabled iff concurrent";
   }
   // Unless required to clear soft references with white references, preserve some white referents.
   if (!clear_soft_references) {
     TimingLogger::ScopedTiming split(concurrent ? "ForwardSoftReferences" :
         "(Paused)ForwardSoftReferences", timings);
     if (concurrent) {
       StartPreservingReferences(self);
     }

     soft_reference_queue_.ForwardSoftReferences(&PreserveSoftReferenceCallback,
                                                 &process_references_args_);
     process_mark_stack_callback(arg);
     if (concurrent) {
       StopPreservingReferences(self);
     }
   }
   // Clear all remaining soft and weak references with white referents.
   soft_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   weak_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   {
     TimingLogger::ScopedTiming t(concurrent ? "EnqueueFinalizerReferences" :
         "(Paused)EnqueueFinalizerReferences", timings);
     if (concurrent) {
       StartPreservingReferences(self);
     }
     // Preserve all white objects with finalize methods and schedule them for finalization.
     finalizer_reference_queue_.EnqueueFinalizerReferences(&cleared_references_, is_marked_callback,
                                                           mark_object_callback, arg);
     process_mark_stack_callback(arg);
     if (concurrent) {
       StopPreservingReferences(self);
     }
   }
   // Clear all finalizer referent reachable soft and weak references with white referents.
   soft_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   weak_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   // Clear all phantom references with white referents.
   phantom_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
   // At this point all reference queues other than the cleared references should be empty.
   DCHECK(soft_reference_queue_.IsEmpty());
   DCHECK(weak_reference_queue_.IsEmpty());
   DCHECK(finalizer_reference_queue_.IsEmpty());
   DCHECK(phantom_reference_queue_.IsEmpty());
   {
     MutexLock mu(self, lock_);
     // Need to always do this since the next GC may be concurrent. Doing this for only concurrent
     // could result in a stale is_marked_callback_ being called before the reference processing
     // starts since there is a small window of time where slow_path_enabled_ is enabled but the
     // callback isn't yet set.
     process_references_args_.is_marked_callback_ = nullptr;
     if (concurrent) {
       // Done processing, disable the slow path and broadcast to the waiters.
       DisableSlowPath(self);
     }
   }
 }

 // Process the "referent" field in a java.lang.ref.Reference.  If the referent has not yet been
 // marked, put it on the appropriate list in the heap for later processing.
 void ReferenceProcessor::DelayReferenceReferent(mirror::Class* klass, mirror::Reference* ref,
                                                 IsHeapReferenceMarkedCallback* is_marked_callback,
                                                 void* arg) {
   // klass can be the class of the old object if the visitor already updated the class of ref.
   DCHECK(klass != nullptr);
   DCHECK(klass->IsTypeOfReferenceClass());
   mirror::HeapReference<mirror::Object>* referent = ref->GetReferentReferenceAddr();
   if (referent->AsMirrorPtr() != nullptr && !is_marked_callback(referent, arg)) {
     Thread* self = Thread::Current();
     // TODO: Remove these locks, and use atomic stacks for storing references?
     // We need to check that the references haven't already been enqueued since we can end up
     // scanning the same reference multiple times due to dirty cards.
     if (klass->IsSoftReferenceClass()) {
       soft_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
     } else if (klass->IsWeakReferenceClass()) {
       weak_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
     } else if (klass->IsFinalizerReferenceClass()) {
       finalizer_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
     } else if (klass->IsPhantomReferenceClass()) {
       phantom_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
     } else {
       LOG(FATAL) << "Invalid reference type " << PrettyClass(klass) << " " << std::hex
                  << klass->GetAccessFlags();
     }
   }
 }

 void ReferenceProcessor::UpdateRoots(IsMarkedCallback* callback, void* arg) {
   cleared_references_.UpdateRoots(callback, arg);
 }

 void ReferenceProcessor::EnqueueClearedReferences(Thread* self) {
   Locks::mutator_lock_->AssertNotHeld(self);
   if (!cleared_references_.IsEmpty()) {
     // When a runtime isn't started there are no reference queues to care about so ignore.
     if (LIKELY(Runtime::Current()->IsStarted())) {
       ScopedObjectAccess soa(self);
       ScopedLocalRef<jobject> arg(self->GetJniEnv(),
                                   soa.AddLocalReference<jobject>(cleared_references_.GetList()));
       jvalue args[1];
       args[0].l = arg.get();
       InvokeWithJValues(soa, nullptr, WellKnownClasses::java_lang_ref_ReferenceQueue_add, args);
     }
     cleared_references_.Clear();
   }
 }

 }  // namespace gc
 }  // namespace art
	/*
	* 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 "reference_processor.h"

	#include "mirror/object-inl.h"
	#include "mirror/reference.h"
	#include "mirror/reference-inl.h"
	#include "reference_processor-inl.h"
	#include "reflection.h"
	#include "ScopedLocalRef.h"
	#include "scoped_thread_state_change.h"
	#include "well_known_classes.h"

	namespace art {
	namespace gc {

	ReferenceProcessor::ReferenceProcessor()
	: process_references_args_(nullptr, nullptr, nullptr),
	preserving_references_(false), lock_("reference processor lock", kReferenceProcessorLock),
	condition_("reference processor condition", lock_) {
	}

	void ReferenceProcessor::EnableSlowPath() {
	mirror::Reference::GetJavaLangRefReference()->SetSlowPath(true);
	}

	void ReferenceProcessor::DisableSlowPath(Thread* self) {
	mirror::Reference::GetJavaLangRefReference()->SetSlowPath(false);
	condition_.Broadcast(self);
	}

	mirror::Object* ReferenceProcessor::GetReferent(Thread* self, mirror::Reference* reference) {
	mirror::Object* const referent = reference->GetReferent();
	// If the referent is null then it is already cleared, we can just return null since there is no
	// scenario where it becomes non-null during the reference processing phase.
	if (UNLIKELY(!SlowPathEnabled()) \|\| referent == nullptr) {
	return referent;
	}
	MutexLock mu(self, lock_);
	while (SlowPathEnabled()) {
	mirror::HeapReference<mirror::Object>* const referent_addr =
	reference->GetReferentReferenceAddr();
	// If the referent became cleared, return it. Don't need barrier since thread roots can't get
	// updated until after we leave the function due to holding the mutator lock.
	if (referent_addr->AsMirrorPtr() == nullptr) {
	return nullptr;
	}
	// Try to see if the referent is already marked by using the is_marked_callback. We can return
	// it to the mutator as long as the GC is not preserving references.
	IsHeapReferenceMarkedCallback* const is_marked_callback =
	process_references_args_.is_marked_callback_;
	if (LIKELY(is_marked_callback != nullptr)) {
	// If it's null it means not marked, but it could become marked if the referent is reachable
	// by finalizer referents. So we can not return in this case and must block. Otherwise, we
	// can return it to the mutator as long as the GC is not preserving references, in which
	// case only black nodes can be safely returned. If the GC is preserving references, the
	// mutator could take a white field from a grey or white node and move it somewhere else
	// in the heap causing corruption since this field would get swept.
	if (is_marked_callback(referent_addr, process_references_args_.arg_)) {
	if (!preserving_references_ \|\|
	(LIKELY(!reference->IsFinalizerReferenceInstance()) && !reference->IsEnqueued())) {
	return referent_addr->AsMirrorPtr();
	}
	}
	}
	condition_.WaitHoldingLocks(self);
	}
	return reference->GetReferent();
	}

	bool ReferenceProcessor::PreserveSoftReferenceCallback(mirror::HeapReference<mirror::Object>* obj,
	void* arg) {
	auto* const args = reinterpret_cast<ProcessReferencesArgs*>(arg);
	// TODO: Add smarter logic for preserving soft references.
	mirror::Object* new_obj = args->mark_callback_(obj->AsMirrorPtr(), args->arg_);
	DCHECK(new_obj != nullptr);
	obj->Assign(new_obj);
	return true;
	}

	void ReferenceProcessor::StartPreservingReferences(Thread* self) {
	MutexLock mu(self, lock_);
	preserving_references_ = true;
	}

	void ReferenceProcessor::StopPreservingReferences(Thread* self) {
	MutexLock mu(self, lock_);
	preserving_references_ = false;
	// We are done preserving references, some people who are blocked may see a marked referent.
	condition_.Broadcast(self);
	}

	// Process reference class instances and schedule finalizations.
	void ReferenceProcessor::ProcessReferences(bool concurrent, TimingLogger* timings,
	bool clear_soft_references,
	IsHeapReferenceMarkedCallback* is_marked_callback,
	MarkObjectCallback* mark_object_callback,
	ProcessMarkStackCallback* process_mark_stack_callback,
	void* arg) {
	TimingLogger::ScopedTiming t(concurrent ? __FUNCTION__ : "(Paused)ProcessReferences", timings);
	Thread* self = Thread::Current();
	{
	MutexLock mu(self, lock_);
	process_references_args_.is_marked_callback_ = is_marked_callback;
	process_references_args_.mark_callback_ = mark_object_callback;
	process_references_args_.arg_ = arg;
	CHECK_EQ(SlowPathEnabled(), concurrent) << "Slow path must be enabled iff concurrent";
	}
	// Unless required to clear soft references with white references, preserve some white referents.
	if (!clear_soft_references) {
	TimingLogger::ScopedTiming split(concurrent ? "ForwardSoftReferences" :
	"(Paused)ForwardSoftReferences", timings);
	if (concurrent) {
	StartPreservingReferences(self);
	}

	soft_reference_queue_.ForwardSoftReferences(&PreserveSoftReferenceCallback,
	&process_references_args_);
	process_mark_stack_callback(arg);
	if (concurrent) {
	StopPreservingReferences(self);
	}
	}
	// Clear all remaining soft and weak references with white referents.
	soft_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
	weak_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
	{
	TimingLogger::ScopedTiming t(concurrent ? "EnqueueFinalizerReferences" :
	"(Paused)EnqueueFinalizerReferences", timings);
	if (concurrent) {
	StartPreservingReferences(self);
	}
	// Preserve all white objects with finalize methods and schedule them for finalization.
	finalizer_reference_queue_.EnqueueFinalizerReferences(&cleared_references_, is_marked_callback,
	mark_object_callback, arg);
	process_mark_stack_callback(arg);
	if (concurrent) {
	StopPreservingReferences(self);
	}
	}
	// Clear all finalizer referent reachable soft and weak references with white referents.
	soft_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
	weak_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
	// Clear all phantom references with white referents.
	phantom_reference_queue_.ClearWhiteReferences(&cleared_references_, is_marked_callback, arg);
	// At this point all reference queues other than the cleared references should be empty.
	DCHECK(soft_reference_queue_.IsEmpty());
	DCHECK(weak_reference_queue_.IsEmpty());
	DCHECK(finalizer_reference_queue_.IsEmpty());
	DCHECK(phantom_reference_queue_.IsEmpty());
	{
	MutexLock mu(self, lock_);
	// Need to always do this since the next GC may be concurrent. Doing this for only concurrent
	// could result in a stale is_marked_callback_ being called before the reference processing
	// starts since there is a small window of time where slow_path_enabled_ is enabled but the
	// callback isn't yet set.
	process_references_args_.is_marked_callback_ = nullptr;
	if (concurrent) {
	// Done processing, disable the slow path and broadcast to the waiters.
	DisableSlowPath(self);
	}
	}
	}

	// Process the "referent" field in a java.lang.ref.Reference. If the referent has not yet been
	// marked, put it on the appropriate list in the heap for later processing.
	void ReferenceProcessor::DelayReferenceReferent(mirror::Class* klass, mirror::Reference* ref,
	IsHeapReferenceMarkedCallback* is_marked_callback,
	void* arg) {
	// klass can be the class of the old object if the visitor already updated the class of ref.
	DCHECK(klass != nullptr);
	DCHECK(klass->IsTypeOfReferenceClass());
	mirror::HeapReference<mirror::Object>* referent = ref->GetReferentReferenceAddr();
	if (referent->AsMirrorPtr() != nullptr && !is_marked_callback(referent, arg)) {
	Thread* self = Thread::Current();
	// TODO: Remove these locks, and use atomic stacks for storing references?
	// We need to check that the references haven't already been enqueued since we can end up
	// scanning the same reference multiple times due to dirty cards.
	if (klass->IsSoftReferenceClass()) {
	soft_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
	} else if (klass->IsWeakReferenceClass()) {
	weak_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
	} else if (klass->IsFinalizerReferenceClass()) {
	finalizer_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
	} else if (klass->IsPhantomReferenceClass()) {
	phantom_reference_queue_.AtomicEnqueueIfNotEnqueued(self, ref);
	} else {
	LOG(FATAL) << "Invalid reference type " << PrettyClass(klass) << " " << std::hex
	<< klass->GetAccessFlags();
	}
	}
	}

	void ReferenceProcessor::UpdateRoots(IsMarkedCallback* callback, void* arg) {
	cleared_references_.UpdateRoots(callback, arg);
	}

	void ReferenceProcessor::EnqueueClearedReferences(Thread* self) {
	Locks::mutator_lock_->AssertNotHeld(self);
	if (!cleared_references_.IsEmpty()) {
	// When a runtime isn't started there are no reference queues to care about so ignore.
	if (LIKELY(Runtime::Current()->IsStarted())) {
	ScopedObjectAccess soa(self);
	ScopedLocalRef<jobject> arg(self->GetJniEnv(),
	soa.AddLocalReference<jobject>(cleared_references_.GetList()));
	jvalue args[1];
	args[0].l = arg.get();
	InvokeWithJValues(soa, nullptr, WellKnownClasses::java_lang_ref_ReferenceQueue_add, args);
	}
	cleared_references_.Clear();
	}
	}

	} // namespace gc
	} // namespace art