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      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 #ifndef ART_RUNTIME_GC_ROOT_H_
     18 #define ART_RUNTIME_GC_ROOT_H_
     19 
     20 #include "base/macros.h"
     21 #include "base/mutex.h"       // For Locks::mutator_lock_.
     22 
     23 namespace art {
     24 
     25 namespace mirror {
     26 class Object;
     27 }  // namespace mirror
     28 
     29 enum RootType {
     30   kRootUnknown = 0,
     31   kRootJNIGlobal,
     32   kRootJNILocal,
     33   kRootJavaFrame,
     34   kRootNativeStack,
     35   kRootStickyClass,
     36   kRootThreadBlock,
     37   kRootMonitorUsed,
     38   kRootThreadObject,
     39   kRootInternedString,
     40   kRootDebugger,
     41   kRootVMInternal,
     42   kRootJNIMonitor,
     43 };
     44 std::ostream& operator<<(std::ostream& os, const RootType& root_type);
     45 
     46 class RootInfo {
     47  public:
     48   // Thread id 0 is for non thread roots.
     49   explicit RootInfo(RootType type, uint32_t thread_id = 0)
     50      : type_(type), thread_id_(thread_id) {
     51   }
     52   virtual ~RootInfo() {
     53   }
     54   RootType GetType() const {
     55     return type_;
     56   }
     57   uint32_t GetThreadId() const {
     58     return thread_id_;
     59   }
     60   virtual void Describe(std::ostream& os) const {
     61     os << "Type=" << type_ << " thread_id=" << thread_id_;
     62   }
     63 
     64  private:
     65   const RootType type_;
     66   const uint32_t thread_id_;
     67 };
     68 
     69 // Returns the new address of the object, returns root if it has not moved. tid and root_type are
     70 // only used by hprof.
     71 typedef void (RootCallback)(mirror::Object** root, void* arg, const RootInfo& root_info);
     72 
     73 template<class MirrorType>
     74 class PACKED(4) GcRoot {
     75  public:
     76   template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
     77   ALWAYS_INLINE MirrorType* Read() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
     78 
     79   void VisitRoot(RootCallback* callback, void* arg, const RootInfo& info) const {
     80     DCHECK(!IsNull());
     81     callback(reinterpret_cast<mirror::Object**>(&root_), arg, info);
     82     DCHECK(!IsNull());
     83   }
     84 
     85   void VisitRootIfNonNull(RootCallback* callback, void* arg, const RootInfo& info) const {
     86     if (!IsNull()) {
     87       VisitRoot(callback, arg, info);
     88     }
     89   }
     90 
     91   // This is only used by IrtIterator.
     92   ALWAYS_INLINE MirrorType** AddressWithoutBarrier() {
     93     return &root_;
     94   }
     95 
     96   bool IsNull() const {
     97     // It's safe to null-check it without a read barrier.
     98     return root_ == nullptr;
     99   }
    100 
    101   ALWAYS_INLINE explicit GcRoot<MirrorType>() : root_(nullptr) {
    102   }
    103 
    104   ALWAYS_INLINE explicit GcRoot<MirrorType>(MirrorType* ref)
    105       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) : root_(ref) {
    106   }
    107 
    108  private:
    109   mutable MirrorType* root_;
    110 };
    111 
    112 }  // namespace art
    113 
    114 #endif  // ART_RUNTIME_GC_ROOT_H_
    115