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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 #include "mirror/object_reference.h"
     23 
     24 namespace art {
     25 
     26 namespace mirror {
     27 class Object;
     28 }  // namespace mirror
     29 
     30 template <size_t kBufferSize>
     31 class BufferedRootVisitor;
     32 
     33 // Dependent on pointer size so that we don't have frames that are too big on 64 bit.
     34 static const size_t kDefaultBufferedRootCount = 1024 / sizeof(void*);
     35 
     36 enum RootType {
     37   kRootUnknown = 0,
     38   kRootJNIGlobal,
     39   kRootJNILocal,
     40   kRootJavaFrame,
     41   kRootNativeStack,
     42   kRootStickyClass,
     43   kRootThreadBlock,
     44   kRootMonitorUsed,
     45   kRootThreadObject,
     46   kRootInternedString,
     47   kRootDebugger,
     48   kRootVMInternal,
     49   kRootJNIMonitor,
     50 };
     51 std::ostream& operator<<(std::ostream& os, const RootType& root_type);
     52 
     53 // Only used by hprof. thread_id_ and type_ are only used by hprof.
     54 class RootInfo {
     55  public:
     56   // Thread id 0 is for non thread roots.
     57   explicit RootInfo(RootType type, uint32_t thread_id = 0)
     58      : type_(type), thread_id_(thread_id) {
     59   }
     60   RootInfo(const RootInfo&) = default;
     61   virtual ~RootInfo() {
     62   }
     63   RootType GetType() const {
     64     return type_;
     65   }
     66   uint32_t GetThreadId() const {
     67     return thread_id_;
     68   }
     69   virtual void Describe(std::ostream& os) const {
     70     os << "Type=" << type_ << " thread_id=" << thread_id_;
     71   }
     72   std::string ToString() const;
     73 
     74  private:
     75   const RootType type_;
     76   const uint32_t thread_id_;
     77 };
     78 
     79 inline std::ostream& operator<<(std::ostream& os, const RootInfo& root_info) {
     80   root_info.Describe(os);
     81   return os;
     82 }
     83 
     84 class RootVisitor {
     85  public:
     86   virtual ~RootVisitor() { }
     87 
     88   // Single root version, not overridable.
     89   ALWAYS_INLINE void VisitRoot(mirror::Object** roots, const RootInfo& info)
     90       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     91     VisitRoots(&roots, 1, info);
     92   }
     93 
     94   // Single root version, not overridable.
     95   ALWAYS_INLINE void VisitRootIfNonNull(mirror::Object** roots, const RootInfo& info)
     96       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     97     if (*roots != nullptr) {
     98       VisitRoot(roots, info);
     99     }
    100   }
    101 
    102   virtual void VisitRoots(mirror::Object*** roots, size_t count, const RootInfo& info)
    103       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) = 0;
    104 
    105   virtual void VisitRoots(mirror::CompressedReference<mirror::Object>** roots, size_t count,
    106                           const RootInfo& info)
    107       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) = 0;
    108 };
    109 
    110 // Only visits roots one at a time, doesn't handle updating roots. Used when performance isn't
    111 // critical.
    112 class SingleRootVisitor : public RootVisitor {
    113  private:
    114   void VisitRoots(mirror::Object*** roots, size_t count, const RootInfo& info) OVERRIDE
    115       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    116     for (size_t i = 0; i < count; ++i) {
    117       VisitRoot(*roots[i], info);
    118     }
    119   }
    120 
    121   void VisitRoots(mirror::CompressedReference<mirror::Object>** roots, size_t count,
    122                           const RootInfo& info) OVERRIDE
    123       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    124     for (size_t i = 0; i < count; ++i) {
    125       VisitRoot(roots[i]->AsMirrorPtr(), info);
    126     }
    127   }
    128 
    129   virtual void VisitRoot(mirror::Object* root, const RootInfo& info) = 0;
    130 };
    131 
    132 template<class MirrorType>
    133 class GcRoot {
    134  public:
    135   template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
    136   ALWAYS_INLINE MirrorType* Read() const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
    137 
    138   void VisitRoot(RootVisitor* visitor, const RootInfo& info) const
    139       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    140     DCHECK(!IsNull());
    141     mirror::CompressedReference<mirror::Object>* roots[1] = { &root_ };
    142     visitor->VisitRoots(roots, 1u, info);
    143     DCHECK(!IsNull());
    144   }
    145 
    146   void VisitRootIfNonNull(RootVisitor* visitor, const RootInfo& info) const
    147       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    148     if (!IsNull()) {
    149       VisitRoot(visitor, info);
    150     }
    151   }
    152 
    153   ALWAYS_INLINE mirror::CompressedReference<mirror::Object>* AddressWithoutBarrier() {
    154     return &root_;
    155   }
    156 
    157   ALWAYS_INLINE bool IsNull() const {
    158     // It's safe to null-check it without a read barrier.
    159     return root_.IsNull();
    160   }
    161 
    162   ALWAYS_INLINE GcRoot(MirrorType* ref = nullptr) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_);
    163 
    164  private:
    165   // Root visitors take pointers to root_ and place the min CompressedReference** arrays. We use a
    166   // CompressedReference<mirror::Object> here since it violates strict aliasing requirements to
    167   // cast CompressedReference<MirrorType>* to CompressedReference<mirror::Object>*.
    168   mutable mirror::CompressedReference<mirror::Object> root_;
    169 
    170   template <size_t kBufferSize> friend class BufferedRootVisitor;
    171 };
    172 
    173 // Simple data structure for buffered root visiting to avoid virtual dispatch overhead. Currently
    174 // only for CompressedReferences since these are more common than the Object** roots which are only
    175 // for thread local roots.
    176 template <size_t kBufferSize>
    177 class BufferedRootVisitor {
    178  public:
    179   BufferedRootVisitor(RootVisitor* visitor, const RootInfo& root_info)
    180       : visitor_(visitor), root_info_(root_info), buffer_pos_(0) {
    181   }
    182 
    183   ~BufferedRootVisitor() {
    184     Flush();
    185   }
    186 
    187   template <class MirrorType>
    188   ALWAYS_INLINE void VisitRootIfNonNull(GcRoot<MirrorType>& root)
    189       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    190     if (!root.IsNull()) {
    191       VisitRoot(root);
    192     }
    193   }
    194 
    195   template <class MirrorType>
    196   ALWAYS_INLINE void VisitRootIfNonNull(mirror::CompressedReference<MirrorType>* root)
    197       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    198     if (!root->IsNull()) {
    199       VisitRoot(root);
    200     }
    201   }
    202 
    203   template <class MirrorType>
    204   void VisitRoot(GcRoot<MirrorType>& root) SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    205     VisitRoot(root.AddressWithoutBarrier());
    206   }
    207 
    208   template <class MirrorType>
    209   void VisitRoot(mirror::CompressedReference<MirrorType>* root)
    210       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    211     if (UNLIKELY(buffer_pos_ >= kBufferSize)) {
    212       Flush();
    213     }
    214     roots_[buffer_pos_++] = root;
    215   }
    216 
    217   void Flush() SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
    218     visitor_->VisitRoots(roots_, buffer_pos_, root_info_);
    219     buffer_pos_ = 0;
    220   }
    221 
    222  private:
    223   RootVisitor* const visitor_;
    224   RootInfo root_info_;
    225   mirror::CompressedReference<mirror::Object>* roots_[kBufferSize];
    226   size_t buffer_pos_;
    227 };
    228 
    229 }  // namespace art
    230 
    231 #endif  // ART_RUNTIME_GC_ROOT_H_
    232