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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_COLLECTOR_IMMUNE_REGION_H_
     18 #define ART_RUNTIME_GC_COLLECTOR_IMMUNE_REGION_H_
     19 
     20 #include "base/macros.h"
     21 #include "base/mutex.h"
     22 
     23 namespace art {
     24 namespace mirror {
     25 class Object;
     26 }  // namespace mirror
     27 namespace gc {
     28 namespace space {
     29 class ContinuousSpace;
     30 }  // namespace space
     31 
     32 namespace collector {
     33 
     34 // An immune region is a continuous region of memory for which all objects contained are assumed to
     35 // be marked. This is used as an optimization in the GC to avoid needing to test the mark bitmap of
     36 // the zygote, image spaces, and sometimes non moving spaces. Doing the ContainsObject check is
     37 // faster than doing a bitmap read. There is no support for discontinuous spaces and you need to be
     38 // careful that your immune region doesn't contain any large objects.
     39 class ImmuneRegion {
     40  public:
     41   ImmuneRegion();
     42 
     43   void Reset();
     44 
     45   // Returns true if an object is inside of the immune region (assumed to be marked).
     46   ALWAYS_INLINE bool ContainsObject(const mirror::Object* obj) const {
     47     // Note: Relies on integer underflow behavior.
     48     return reinterpret_cast<uintptr_t>(obj) - reinterpret_cast<uintptr_t>(begin_) < size_;
     49   }
     50 
     51   void SetBegin(mirror::Object* begin) {
     52     begin_ = begin;
     53     UpdateSize();
     54   }
     55 
     56   void SetEnd(mirror::Object* end) {
     57     end_ = end;
     58     UpdateSize();
     59   }
     60 
     61   mirror::Object* Begin() const {
     62     return begin_;
     63   }
     64 
     65   mirror::Object* End() const {
     66     return end_;
     67   }
     68 
     69   size_t Size() const {
     70     return size_;
     71   }
     72 
     73  private:
     74   void UpdateSize() {
     75     size_ = reinterpret_cast<uintptr_t>(end_) - reinterpret_cast<uintptr_t>(begin_);
     76   }
     77 
     78   mirror::Object* begin_;
     79   mirror::Object* end_;
     80   uintptr_t size_;
     81 };
     82 
     83 }  // namespace collector
     84 }  // namespace gc
     85 }  // namespace art
     86 
     87 #endif  // ART_RUNTIME_GC_COLLECTOR_IMMUNE_REGION_H_
     88