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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_READ_BARRIER_H_
     18 #define ART_RUNTIME_READ_BARRIER_H_
     19 
     20 #include "base/mutex.h"
     21 #include "base/macros.h"
     22 #include "gc_root.h"
     23 #include "jni.h"
     24 #include "mirror/object_reference.h"
     25 #include "offsets.h"
     26 #include "read_barrier_c.h"
     27 
     28 // This is a C++ (not C) header file, separate from read_barrier_c.h
     29 // which needs to be a C header file for asm_support.h.
     30 
     31 namespace art {
     32 namespace mirror {
     33   class Object;
     34   template<typename MirrorType> class HeapReference;
     35 }  // namespace mirror
     36 class ArtMethod;
     37 
     38 class ReadBarrier {
     39  public:
     40   // Enable the to-space invariant checks.
     41   static constexpr bool kEnableToSpaceInvariantChecks = kIsDebugBuild;
     42   // Enable the read barrier checks.
     43   static constexpr bool kEnableReadBarrierInvariantChecks = kIsDebugBuild;
     44 
     45   // It's up to the implementation whether the given field gets updated whereas the return value
     46   // must be an updated reference unless kAlwaysUpdateField is true.
     47   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier,
     48             bool kAlwaysUpdateField = false>
     49   ALWAYS_INLINE static MirrorType* Barrier(
     50       mirror::Object* obj, MemberOffset offset, mirror::HeapReference<MirrorType>* ref_addr)
     51       REQUIRES_SHARED(Locks::mutator_lock_);
     52 
     53   // It's up to the implementation whether the given root gets updated
     54   // whereas the return value must be an updated reference.
     55   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
     56   ALWAYS_INLINE static MirrorType* BarrierForRoot(MirrorType** root,
     57                                                   GcRootSource* gc_root_source = nullptr)
     58       REQUIRES_SHARED(Locks::mutator_lock_);
     59 
     60   // It's up to the implementation whether the given root gets updated
     61   // whereas the return value must be an updated reference.
     62   template <typename MirrorType, ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
     63   ALWAYS_INLINE static MirrorType* BarrierForRoot(mirror::CompressedReference<MirrorType>* root,
     64                                                   GcRootSource* gc_root_source = nullptr)
     65       REQUIRES_SHARED(Locks::mutator_lock_);
     66 
     67   // Return the mirror Object if it is marked, or null if not.
     68   template <typename MirrorType>
     69   ALWAYS_INLINE static MirrorType* IsMarked(MirrorType* ref)
     70       REQUIRES_SHARED(Locks::mutator_lock_);
     71 
     72   static bool IsDuringStartup();
     73 
     74   // Without the holder object.
     75   static void AssertToSpaceInvariant(mirror::Object* ref)
     76       REQUIRES_SHARED(Locks::mutator_lock_) {
     77     AssertToSpaceInvariant(nullptr, MemberOffset(0), ref);
     78   }
     79   // With the holder object.
     80   static void AssertToSpaceInvariant(mirror::Object* obj, MemberOffset offset,
     81                                      mirror::Object* ref)
     82       REQUIRES_SHARED(Locks::mutator_lock_);
     83   // With GcRootSource.
     84   static void AssertToSpaceInvariant(GcRootSource* gc_root_source, mirror::Object* ref)
     85       REQUIRES_SHARED(Locks::mutator_lock_);
     86 
     87   // ALWAYS_INLINE on this caused a performance regression b/26744236.
     88   static mirror::Object* Mark(mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_);
     89 
     90   static constexpr uint32_t WhiteState() {
     91     return white_state_;
     92   }
     93   static constexpr uint32_t GrayState() {
     94     return gray_state_;
     95   }
     96 
     97   // fake_address_dependency will be zero which should be bitwise-or'ed with the address of the
     98   // subsequent load to prevent the reordering of the read barrier bit load and the subsequent
     99   // object reference load (from one of `obj`'s fields).
    100   // *fake_address_dependency will be set to 0.
    101   ALWAYS_INLINE static bool IsGray(mirror::Object* obj, uintptr_t* fake_address_dependency)
    102       REQUIRES_SHARED(Locks::mutator_lock_);
    103 
    104   // This uses a load-acquire to load the read barrier bit internally to prevent the reordering of
    105   // the read barrier bit load and the subsequent load.
    106   ALWAYS_INLINE static bool IsGray(mirror::Object* obj)
    107       REQUIRES_SHARED(Locks::mutator_lock_);
    108 
    109   static bool IsValidReadBarrierState(uint32_t rb_state) {
    110     return rb_state == white_state_ || rb_state == gray_state_;
    111   }
    112 
    113   static constexpr uint32_t white_state_ = 0x0;    // Not marked.
    114   static constexpr uint32_t gray_state_ = 0x1;     // Marked, but not marked through. On mark stack.
    115   static constexpr uint32_t rb_state_mask_ = 0x1;  // The low bits for white|gray.
    116 };
    117 
    118 }  // namespace art
    119 
    120 #endif  // ART_RUNTIME_READ_BARRIER_H_
    121