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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   void Reset();
     43   bool AddContinuousSpace(space::ContinuousSpace* space)
     44       EXCLUSIVE_LOCKS_REQUIRED(Locks::heap_bitmap_lock_);
     45   bool ContainsSpace(const space::ContinuousSpace* space) const;
     46   // Returns true if an object is inside of the immune region (assumed to be marked).
     47   bool ContainsObject(const mirror::Object* obj) const ALWAYS_INLINE {
     48     // Note: Relies on integer underflow behavior.
     49     return reinterpret_cast<uintptr_t>(obj) - reinterpret_cast<uintptr_t>(begin_) < size_;
     50   }
     51   void SetBegin(mirror::Object* begin) {
     52     begin_ = begin;
     53     UpdateSize();
     54   }
     55   void SetEnd(mirror::Object* end) {
     56     end_ = end;
     57     UpdateSize();
     58   }
     59 
     60  private:
     61   bool IsEmpty() const {
     62     return size_ == 0;
     63   }
     64   void UpdateSize() {
     65     size_ = reinterpret_cast<uintptr_t>(end_) - reinterpret_cast<uintptr_t>(begin_);
     66   }
     67 
     68   mirror::Object* begin_;
     69   mirror::Object* end_;
     70   uintptr_t size_;
     71 };
     72 
     73 }  // namespace collector
     74 }  // namespace gc
     75 }  // namespace art
     76 
     77 #endif  // ART_RUNTIME_GC_COLLECTOR_IMMUNE_REGION_H_
     78