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) {
}
};
