gc/accounting/space_bitmap.h

/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ART_RUNTIME_GC_ACCOUNTING_SPACE_BITMAP_H_
#define ART_RUNTIME_GC_ACCOUNTING_SPACE_BITMAP_H_

#include <limits.h>
#include <stdint.h>
#include <memory>
#include <set>
#include <vector>

#include "base/mutex.h"
#include "globals.h"
#include "object_callbacks.h"

namespace art {

namespace mirror {
  class Class;
  class Object;
}  // namespace mirror
class MemMap;

namespace gc {
namespace accounting {

template<size_t kAlignment>
class SpaceBitmap {
 public:
  typedef void ScanCallback(mirror::Object* obj, void* finger, void* arg);
  typedef void SweepCallback(size_t ptr_count, mirror::Object** ptrs, void* arg);

  // Initialize a space bitmap so that it points to a bitmap large enough to cover a heap at
  // heap_begin of heap_capacity bytes, where objects are guaranteed to be kAlignment-aligned.
  static SpaceBitmap* Create(const std::string& name, uint8_t* heap_begin, size_t heap_capacity);

  // Initialize a space bitmap using the provided mem_map as the live bits. Takes ownership of the
  // mem map. The address range covered starts at heap_begin and is of size equal to heap_capacity.
  // Objects are kAlignement-aligned.
  static SpaceBitmap* CreateFromMemMap(const std::string& name, MemMap* mem_map,
                                       uint8_t* heap_begin, size_t heap_capacity);

  ~SpaceBitmap();

  // <offset> is the difference from .base to a pointer address.
  // <index> is the index of .bits that contains the bit representing
  //         <offset>.
  static constexpr size_t OffsetToIndex(size_t offset) {
    return offset / kAlignment / kBitsPerIntPtrT;
  }

  template<typename T>
  static constexpr T IndexToOffset(T index) {
    return static_cast<T>(index * kAlignment * kBitsPerIntPtrT);
  }

  ALWAYS_INLINE static constexpr uintptr_t OffsetBitIndex(uintptr_t offset) {
    return (offset / kAlignment) % kBitsPerIntPtrT;
  }

  // Bits are packed in the obvious way.
  static constexpr uintptr_t OffsetToMask(uintptr_t offset) {
    return static_cast<size_t>(1) << OffsetBitIndex(offset);
  }

  bool Set(const mirror::Object* obj) ALWAYS_INLINE {
    return Modify<true>(obj);
  }

  bool Clear(const mirror::Object* obj) ALWAYS_INLINE {
    return Modify<false>(obj);
  }

  // Returns true if the object was previously marked.
  bool AtomicTestAndSet(const mirror::Object* obj);

  // Fill the bitmap with zeroes.  Returns the bitmap's memory to the system as a side-effect.
  void Clear();

  // Clear a covered by the bitmap using madvise if possible.
  void ClearRange(const mirror::Object* begin, const mirror::Object* end);

  bool Test(const mirror::Object* obj) const;

  // Return true iff <obj> is within the range of pointers that this bitmap could potentially cover,
  // even if a bit has not been set for it.
  bool HasAddress(const void* obj) const {
    // If obj < heap_begin_ then offset underflows to some very large value past the end of the
    // bitmap.
    const uintptr_t offset = reinterpret_cast<uintptr_t>(obj) - heap_begin_;
    const size_t index = OffsetToIndex(offset);
    return index < bitmap_size_ / sizeof(intptr_t);
  }

  void VisitRange(uintptr_t base, uintptr_t max, ObjectCallback* callback, void* arg) const;

  class ClearVisitor {
   public:
    explicit ClearVisitor(SpaceBitmap* const bitmap)
        : bitmap_(bitmap) {
    }

    void operator()(mirror::Object* obj) const {
      bitmap_->Clear(obj);
    }
   private:
    SpaceBitmap* const bitmap_;
  };

  template <typename Visitor>
  void VisitRange(uintptr_t visit_begin, uintptr_t visit_end, const Visitor& visitor) const {
    for (; visit_begin < visit_end; visit_begin += kAlignment) {
      visitor(reinterpret_cast<mirror::Object*>(visit_begin));
    }
  }

  // Visit the live objects in the range [visit_begin, visit_end).
  // TODO: Use lock annotations when clang is fixed.
  // REQUIRES(Locks::heap_bitmap_lock_) REQUIRES_SHARED(Locks::mutator_lock_);
  template <typename Visitor>
  void VisitMarkedRange(uintptr_t visit_begin, uintptr_t visit_end, const Visitor& visitor) const
      NO_THREAD_SAFETY_ANALYSIS;

  // Visits set bits in address order.  The callback is not permitted to change the bitmap bits or
  // max during the traversal.
  void Walk(ObjectCallback* callback, void* arg)
      REQUIRES_SHARED(Locks::heap_bitmap_lock_);

  // Walk through the bitmaps in increasing address order, and find the object pointers that
  // correspond to garbage objects.  Call <callback> zero or more times with lists of these object
  // pointers. The callback is not permitted to increase the max of either bitmap.
  static void SweepWalk(const SpaceBitmap& live, const SpaceBitmap& mark, uintptr_t base,
                        uintptr_t max, SweepCallback* thunk, void* arg);

  void CopyFrom(SpaceBitmap* source_bitmap);

  // Starting address of our internal storage.
  Atomic<uintptr_t>* Begin() {
    return bitmap_begin_;
  }

  // Size of our internal storage
  size_t Size() const {
    return bitmap_size_;
  }

  // Size in bytes of the memory that the bitmaps spans.
  uint64_t HeapSize() const {
    return IndexToOffset<uint64_t>(Size() / sizeof(intptr_t));
  }

  void SetHeapSize(size_t bytes) {
    // TODO: Un-map the end of the mem map.
    bitmap_size_ = OffsetToIndex(bytes) * sizeof(intptr_t);
    CHECK_EQ(HeapSize(), bytes);
  }

  uintptr_t HeapBegin() const {
    return heap_begin_;
  }

  // The maximum address which the bitmap can span. (HeapBegin() <= object < HeapLimit()).
  uint64_t HeapLimit() const {
    return static_cast<uint64_t>(HeapBegin()) + HeapSize();
  }

  // Set the max address which can covered by the bitmap.
  void SetHeapLimit(uintptr_t new_end);

  std::string GetName() const {
    return name_;
  }

  void SetName(const std::string& name) {
    name_ = name;
  }

  std::string Dump() const;

  // Helper function for computing bitmap size based on a 64 bit capacity.
  static size_t ComputeBitmapSize(uint64_t capacity);
  static size_t ComputeHeapSize(uint64_t bitmap_bytes);

 private:
  // TODO: heap_end_ is initialized so that the heap bitmap is empty, this doesn't require the -1,
  // however, we document that this is expected on heap_end_
  SpaceBitmap(const std::string& name, MemMap* mem_map, uintptr_t* bitmap_begin, size_t bitmap_size,
              const void* heap_begin);

  template<bool kSetBit>
  bool Modify(const mirror::Object* obj);

  // Backing storage for bitmap.
  std::unique_ptr<MemMap> mem_map_;

  // This bitmap itself, word sized for efficiency in scanning.
  Atomic<uintptr_t>* const bitmap_begin_;

  // Size of this bitmap.
  size_t bitmap_size_;

  // The base address of the heap, which corresponds to the word containing the first bit in the
  // bitmap.
  const uintptr_t heap_begin_;

  // Name of this bitmap.
  std::string name_;
};

typedef SpaceBitmap<kObjectAlignment> ContinuousSpaceBitmap;
typedef SpaceBitmap<kLargeObjectAlignment> LargeObjectBitmap;

template<size_t kAlignment>
std::ostream& operator << (std::ostream& stream, const SpaceBitmap<kAlignment>& bitmap);

}  // namespace accounting
}  // namespace gc
}  // namespace art

#endif  // ART_RUNTIME_GC_ACCOUNTING_SPACE_BITMAP_H_