art虚拟机通过mmap申请的内存使用MemMap表示。它封装了和内存映射有关的操作。

class MemMap {
 public:
  // Releases the memory mapping.
  ~MemMap() REQUIRES(!MemMap::mem_maps_lock_);

  // Set a debug friendly name for a map. It will be prefixed with "dalvik-".
  static void SetDebugName(void* map_ptr, const char* name, size_t size);


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

 
  int GetProtect() const {
    return prot_;
  }

  uint8_t* Begin() const {
    return begin_;
  }

  size_t Size() const {
    return size_;
  }

  // Resize the mem-map by unmapping pages at the end. Currently only supports shrinking.
  void SetSize(size_t new_size);

  uint8_t* End() const {
    return Begin() + Size();
  }

  void* BaseBegin() const {
    return base_begin_;
  }

  size_t BaseSize() const {
    return base_size_;
  }

  void* BaseEnd() const {
    return reinterpret_cast<uint8_t*>(BaseBegin()) + BaseSize();
  }

  bool HasAddress(const void* addr) const {
    return Begin() <= addr && addr < End();
  }

  

  static bool CheckNoGaps(MemMap& begin_map, MemMap& end_map)
      REQUIRES(!MemMap::mem_maps_lock_);
  static void DumpMaps(std::ostream& os, bool terse = false)
      REQUIRES(!MemMap::mem_maps_lock_);

  
  // Align the map by unmapping the unaligned parts at the lower and the higher ends.
  void AlignBy(size_t size);

  // For annotation reasons.
  static std::mutex* GetMemMapsLock() RETURN_CAPABILITY(mem_maps_lock_) {
    return nullptr;
  }

  // Reset in a forked process the MemMap whose memory has been madvised MADV_DONTFORK
  // in the parent process.
  void ResetInForkedProcess();

 private:

  std::string name_;
  uint8_t* begin_ = nullptr;    // Start of data. May be changed by AlignBy.
  size_t size_ = 0u;            // Length of data.

  void* base_begin_ = nullptr;  // Page-aligned base address. May be changed by AlignBy.
  size_t base_size_ = 0u;       // Length of mapping. May be changed by RemapAtEnd (ie Zygote).
  int prot_ = 0;                // Protection of the map.

  // When reuse_ is true, this is just a view of an existing mapping
  // and we do not take ownership and are not responsible for
  // unmapping.
  bool reuse_ = false;
  // When already_unmapped_ is true the destructor will not call munmap.
  bool already_unmapped_ = false;
  size_t redzone_size_ = 0u;

  static std::mutex* mem_maps_lock_;


};

art/runtime/gc/space/space.h:80

class Space {
 public:
  // Name of the space. May vary, for example before/after the Zygote fork.
  const char* GetName() const {
    return name_.c_str();
  }
  // The policy of when objects are collected associated with this space.
  GcRetentionPolicy GetGcRetentionPolicy() const {
    return gc_retention_policy_;
  }
  // Is the given object contained within this space?
  virtual bool Contains(const mirror::Object* obj) const = 0;
  // The kind of space this: image, alloc, zygote, large object.
  virtual SpaceType GetType() const = 0;

  // Returns true if objects in the space are movable.
  virtual bool CanMoveObjects() const = 0;

  virtual ~Space() {}

 protected:
  Space(const std::string& name, GcRetentionPolicy gc_retention_policy);

  void SetGcRetentionPolicy(GcRetentionPolicy gc_retention_policy) {
    gc_retention_policy_ = gc_retention_policy;
  }

  // Name of the space that may vary due to the Zygote fork.
  std::string name_;

 protected:
  // When should objects within this space be reclaimed? Not constant as we vary it in the case
  // of Zygote forking.
  GcRetentionPolicy gc_retention_policy_;
};

Space代表内存空间，是art虚拟机所有内存对象的基类,通过函数GetType获取具体类型。里面存放的都是java世界的对象，包含类，数组等。

space.h:69

enum SpaceType {
  kSpaceTypeImageSpace, 
  kSpaceTypeMallocSpace,
  kSpaceTypeZygoteSpace,
  kSpaceTypeBumpPointerSpace,
  kSpaceTypeLargeObjectSpace,
  kSpaceTypeRegionSpace,
};

这些类型对应的子类分别为ImageSpace，DlMallocSpace，ZygoteSpace，BumpPointerSpace，LargeObjectSpace和RegionSpace。

class AllocSpace {
 public:
  // Number of bytes currently allocated.
  virtual uint64_t GetBytesAllocated() = 0;
  // Number of objects currently allocated.
  virtual uint64_t GetObjectsAllocated() = 0;

 
  // This is what is to be added to Heap::num_bytes_allocated_.
  virtual mirror::Object* Alloc(Thread* self, size_t num_bytes, size_t* bytes_allocated,
                                size_t* usable_size, size_t* bytes_tl_bulk_allocated) = 0;

  // Thread-unsafe allocation for when mutators are suspended, used by the semispace collector.
  virtual mirror::Object* AllocThreadUnsafe(Thread* self, size_t num_bytes, size_t* bytes_allocated,
                                            size_t* usable_size,
                                            size_t* bytes_tl_bulk_allocated)
      REQUIRES(Locks::mutator_lock_) {
    return Alloc(self, num_bytes, bytes_allocated, usable_size, bytes_tl_bulk_allocated);
  }

  // Return the storage space required by obj.
  virtual size_t AllocationSize(mirror::Object* obj, size_t* usable_size) = 0;

  // Returns how many bytes were freed.
  virtual size_t Free(Thread* self, mirror::Object* ptr) = 0;

  // Free (deallocate) all objects in a list, and return the number of bytes freed.
  virtual size_t FreeList(Thread* self, size_t num_ptrs, mirror::Object** ptrs) = 0;

  // Revoke any sort of thread-local buffers that are used to speed up allocations for the given
  // thread, if the alloc space implementation uses any.
  // Returns the total free bytes in the revoked thread local runs that's to be subtracted
  // from Heap::num_bytes_allocated_ or zero if unnecessary.
  virtual size_t RevokeThreadLocalBuffers(Thread* thread) = 0;

  // Revoke any sort of thread-local buffers that are used to speed up allocations for all the
  // threads, if the alloc space implementation uses any.
  // Returns the total free bytes in the revoked thread local runs that's to be subtracted
  // from Heap::num_bytes_allocated_ or zero if unnecessary.
  virtual size_t RevokeAllThreadLocalBuffers() = 0;

  // Compute largest free contiguous chunk of memory available in the space and
  // log it if it's smaller than failed_alloc_bytes and return true.
  // Otherwise leave os untouched and return false.
  virtual bool LogFragmentationAllocFailure(std::ostream& os, size_t failed_alloc_bytes) = 0;

 protected:
  struct SweepCallbackContext {
    SweepCallbackContext(bool swap_bitmaps, space::Space* space);
    const bool swap_bitmaps;
    space::Space* const space;
    Thread* const self;
    collector::ObjectBytePair freed;
  };

  AllocSpace() {}
  virtual ~AllocSpace() {}

};

AllocSpace提供分配和释放内存的接口。

Space派生ContinuousSpace和DiscontinuousSpace两个子类。ContinuousSpace表示连续的内存空间。

DiscontinuousSpace则表示地址不连续，用于分配大的内存。

art/runtime/gc/space/space.h:269

class ContinuousSpace : public Space {
 public:
  // Address at which the space begins.
  uint8_t* Begin() const {
    return begin_;
  }

  // Current address at which the space ends, which may vary as the space is filled.
  uint8_t* End() const {
    return end_.load(std::memory_order_relaxed);
  }

  // The end of the address range covered by the space.
  uint8_t* Limit() const {
    return limit_;
  }

  // Change the end of the space. Be careful with use since changing the end of a space to an
  // invalid value may break the GC.
  void SetEnd(uint8_t* end) {
    end_.store(end, std::memory_order_relaxed);
  }

  void SetLimit(uint8_t* limit) {
    limit_ = limit;
  }

  // Current size of space
  size_t Size() const {
    return End() - Begin();
  }

  virtual accounting::ContinuousSpaceBitmap* GetLiveBitmap() = 0;
  virtual accounting::ContinuousSpaceBitmap* GetMarkBitmap() = 0;

  // Maximum which the mapped space can grow to.
  virtual size_t Capacity() const {
    return Limit() - Begin();
  }

  // Is object within this space? We check to see if the pointer is beyond the end first as
  // continuous spaces are iterated over from low to high.
  bool HasAddress(const mirror::Object* obj) const {
    const uint8_t* byte_ptr = reinterpret_cast<const uint8_t*>(obj);
    return byte_ptr >= Begin() && byte_ptr < Limit();
  }

  bool Contains(const mirror::Object* obj) const {
    return HasAddress(obj);
  }

  virtual bool IsContinuousSpace() const {
    return true;
  }

  bool HasBoundBitmaps() REQUIRES(Locks::heap_bitmap_lock_);

  virtual ~ContinuousSpace() {}

 protected:
  ContinuousSpace(const std::string& name, GcRetentionPolicy gc_retention_policy,
                  uint8_t* begin, uint8_t* end, uint8_t* limit) :
      Space(name, gc_retention_policy), begin_(begin), end_(end), limit_(limit) {
  }

  // The beginning of the storage for fast access.
  uint8_t* begin_;

  // Current end of the space.
  Atomic<uint8_t*> end_;

  // Limit of the space.
  uint8_t* limit_;

};

class DiscontinuousSpace : public Space {

  virtual ~DiscontinuousSpace() {}

  accounting::LargeObjectBitmap live_bitmap_;
  accounting::LargeObjectBitmap mark_bitmap_;
};

ContinuousSpace又有唯一子类MemMapSpace,mem_map_保存的空间信息。

class MemMapSpace : public ContinuousSpace {
 public:
  // Size of the space without a limit on its growth. By default this is just the Capacity, but
  // for the allocation space we support starting with a small heap and then extending it.
  virtual size_t NonGrowthLimitCapacity() const {
    return Capacity();
  }

  MemMap* GetMemMap() {
    return &mem_map_;
  }
  const MemMap* GetMemMap() const {
    return &mem_map_;
  }

  MemMap ReleaseMemMap() {
    return std::move(mem_map_);
  }

 protected:
  MemMapSpace(const std::string& name,
              MemMap&& mem_map,
              uint8_t* begin,
              uint8_t* end,
              uint8_t* limit,
              GcRetentionPolicy gc_retention_policy)
      : ContinuousSpace(name, gc_retention_policy, begin, end, limit),
        mem_map_(std::move(mem_map)) {
  }

  // Underlying storage of the space
  MemMap mem_map_;
};

LargeObjectSpace是DiscontinuousSpace的子类，同时继承了AllocSpace。

art/runtime/gc/space/image_space.h:35

class LargeObjectSpace : public DiscontinuousSpace, public AllocSpace {

  virtual ~LargeObjectSpace() {}

  uint64_t GetBytesAllocated() override {
    MutexLock mu(Thread::Current(), lock_);
    return num_bytes_allocated_;
  }
  uint64_t GetObjectsAllocated() override {
    MutexLock mu(Thread::Current(), lock_);
    return num_objects_allocated_;
  }
  uint64_t GetTotalBytesAllocated() const {
    MutexLock mu(Thread::Current(), lock_);
    return total_bytes_allocated_;
  }
  uint64_t GetTotalObjectsAllocated() const {
    MutexLock mu(Thread::Current(), lock_);
    return total_objects_allocated_;
  }

  bool CanMoveObjects() const override {
    return false;
  }
  // Current address at which the space begins, which may vary as the space is filled.
  uint8_t* Begin() const {
    return begin_;
  }
  // Current address at which the space ends, which may vary as the space is filled.
  uint8_t* End() const {
    return end_;
  }
  // Current size of space
  size_t Size() const {
    return End() - Begin();
  }
  // Return true if we contain the specified address.
  bool Contains(const mirror::Object* obj) const override {
    const uint8_t* byte_obj = reinterpret_cast<const uint8_t*>(obj);
    return Begin() <= byte_obj && byte_obj < End();
  }
 
 protected:

  // Number of bytes which have been allocated into the space and not yet freed. The count is also
  // included in the identically named field in Heap. Counts actual allocated (after rounding),
  // not requested, sizes. TODO: It would be cheaper to just maintain total allocated and total
  // free counts.
  uint64_t num_bytes_allocated_ GUARDED_BY(lock_);
  uint64_t num_objects_allocated_ GUARDED_BY(lock_);

  // Totals for large objects ever allocated, including those that have since been deallocated.
  // Never decremented.
  uint64_t total_bytes_allocated_ GUARDED_BY(lock_);
  uint64_t total_objects_allocated_ GUARDED_BY(lock_);

  // Begin and end, may change as more large objects are allocated.
  uint8_t* begin_;
  uint8_t* end_;
};

MemMapSpace派生出ImgeSpace和ContinuousMemMapAllocSpace。
ContinuousMemMapAllocSpace还继承了AllocSpace。是所有连续的可分配释放的空间的共同父类。ImageSpace空间确定后不发生改变,用于加载和保存art文件信息。

class ImageSpace : public MemMapSpace {
 public:
  SpaceType GetType() const override {
    return kSpaceTypeImageSpace;
  }
  // Try to open an existing app image space for an oat file,
  // using the boot image spaces from the current Runtime.
  static std::unique_ptr<ImageSpace> CreateFromAppImage(const char* image,
                                                        const OatFile* oat_file,
                                                        std::string* error_msg)
      REQUIRES_SHARED(Locks::mutator_lock_);

  // Checks whether we have a primary boot image on the disk.
  static bool IsBootClassPathOnDisk(InstructionSet image_isa);

  // Give access to the OatFile.
  const OatFile* GetOatFile() const;

  // Releases the OatFile from the ImageSpace so it can be transfer to
  // the caller, presumably the OatFileManager.
  std::unique_ptr<const OatFile> ReleaseOatFile();

  void VerifyImageAllocations()
      REQUIRES_SHARED(Locks::mutator_lock_);

  const ImageHeader& GetImageHeader() const {
    return *reinterpret_cast<ImageHeader*>(Begin());
  }

  // Actual filename where image was loaded from.
  // For example: /data/dalvik-cache/arm/system@framework@boot.art
  const std::string GetImageFilename() const {
    return GetName();
  }

  // Symbolic location for image.
  // For example: /system/framework/boot.art
  const std::string GetImageLocation() const {
    return image_location_;
  }

  const std::string GetProfileFile() const {
    return profile_file_;
  }

  accounting::ContinuousSpaceBitmap* GetLiveBitmap() override {
    return &live_bitmap_;
  }


  // Compute the number of components in the image (contributing jar files).
  size_t GetComponentCount() const {
    return GetImageHeader().GetComponentCount();
  }




  bool CanMoveObjects() const override {
    return false;
  }

  // Returns the filename of the image corresponding to
  // requested image_location, or the filename where a new image
  // should be written if one doesn't exist. Looks for a generated
  // image in the specified location and then in the dalvik-cache.
  //
  // Returns true if an image was found, false otherwise.
  static bool FindImageFilename(const char* image_location,
                                InstructionSet image_isa,
                                std::string* system_location,
                                bool* has_system);

  // The leading character in an image checksum part of boot class path checksums.
  static constexpr char kImageChecksumPrefix = 'i';
  // The leading character in a dex file checksum part of boot class path checksums.
  static constexpr char kDexFileChecksumPrefix = 'd';

  // Returns the checksums for the boot image, extensions and extra boot class path dex files,
  // based on the image spaces and boot class path dex files loaded in memory.
  // The `image_spaces` must correspond to the head of the `boot_class_path`.
  static std::string GetBootClassPathChecksums(ArrayRef<ImageSpace* const> image_spaces,
                                               ArrayRef<const DexFile* const> boot_class_path);

  // Returns the total number of components (jar files) associated with the image spaces.
  static size_t GetNumberOfComponents(ArrayRef<gc::space::ImageSpace* const> image_spaces);

 
  // This function is exposed for testing purposes.
  static bool ValidateOatFile(const OatFile& oat_file, std::string* error_msg);

  // Return the end of the image which includes non-heap objects such as ArtMethods and ArtFields.
  uint8_t* GetImageEnd() const {
    return Begin() + GetImageHeader().GetImageSize();
  }

  void DumpSections(std::ostream& os) const;

  // De-initialize the image-space by undoing the effects in Init().
  virtual ~ImageSpace();



 protected:

  static Atomic<uint32_t> bitmap_index_;

  accounting::ContinuousSpaceBitmap live_bitmap_;

  ImageSpace(const std::string& name,
             const char* image_location,
             const char* profile_file,
             MemMap&& mem_map,
             accounting::ContinuousSpaceBitmap&& live_bitmap,
             uint8_t* end);

  // The OatFile associated with the image during early startup to
  // reserve space contiguous to the image. It is later released to
  // the ClassLinker during it's initialization.
  std::unique_ptr<OatFile> oat_file_;

  // There are times when we need to find the boot image oat file. As
  // we release ownership during startup, keep a non-owned reference.
  const OatFile* oat_file_non_owned_;

  const std::string image_location_;
  const std::string profile_file_;

 
}

ContinuousMemMapAllocSpace代表可连续分配的内存资源的空间。

class ContinuousMemMapAllocSpace : public MemMapSpace, public AllocSpace {
 public:

  accounting::ContinuousSpaceBitmap* GetLiveBitmap() override {
    return &live_bitmap_;
  }

  accounting::ContinuousSpaceBitmap* GetMarkBitmap() override {
    return &mark_bitmap_;
  }

  accounting::ContinuousSpaceBitmap* GetTempBitmap() {
    return &temp_bitmap_;
  }


 protected:
  accounting::ContinuousSpaceBitmap live_bitmap_;
  accounting::ContinuousSpaceBitmap mark_bitmap_;
  accounting::ContinuousSpaceBitmap temp_bitmap_;

  ContinuousMemMapAllocSpace(const std::string& name,
                             MemMap&& mem_map,
                             uint8_t* begin,
                             uint8_t* end,
                             uint8_t* limit,
                             GcRetentionPolicy gc_retention_policy)
      : MemMapSpace(name, std::move(mem_map), begin, end, limit, gc_retention_policy) {
  }
};