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* Copyright (C) 2011 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#ifndef ART_SRC_SPACE_H_
#define ART_SRC_SPACE_H_
#include <string>
#include "UniquePtr.h"
#include "globals.h"
#include "image.h"
#include "macros.h"
#include "dlmalloc.h"
#include "mem_map.h"
namespace art {
class AllocSpace;
class ImageSpace;
class Object;
class SpaceBitmap;
enum GcRetentionPolicy {
std::ostream& operator<<(std::ostream& os, const GcRetentionPolicy& policy);
// A space contains memory allocated for managed objects.
class Space {
// Create a AllocSpace with the requested sizes. The requested
// base address is not guaranteed to be granted, if it is required,
// the caller should call Begin on the returned space to confirm
// the request was granted.
static AllocSpace* CreateAllocSpace(const std::string& name, size_t initial_size,
size_t growth_limit, size_t capacity,
byte* requested_begin);
// create a Space from an image file. cannot be used for future allocation or collected.
static ImageSpace* CreateImageSpace(const std::string& image)
virtual ~Space() {}
const std::string& GetSpaceName() const {
return name_;
// Address at which the space begins
byte* Begin() const {
return begin_;
// Address at which the space ends, which may vary as the space is filled
byte* End() const {
return end_;
// Is object within this space?
bool Contains(const Object* obj) const {
const byte* byte_ptr = reinterpret_cast<const byte*>(obj);
return Begin() <= byte_ptr && byte_ptr < End();
// Current size of space
size_t Size() const {
return End() - Begin();
// Maximum size of space
virtual size_t Capacity() const {
return mem_map_->Size();
// 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();
GcRetentionPolicy GetGcRetentionPolicy() const {
return gc_retention_policy_;
void SetGcRetentionPolicy(GcRetentionPolicy gc_retention_policy) {
gc_retention_policy_ = gc_retention_policy;
ImageSpace* AsImageSpace() {
return down_cast<ImageSpace*>(this);
AllocSpace* AsAllocSpace() {
return down_cast<AllocSpace*>(this);
virtual bool IsAllocSpace() const = 0;
virtual bool IsImageSpace() const = 0;
virtual bool IsZygoteSpace() const = 0;
virtual SpaceBitmap* GetLiveBitmap() const = 0;
virtual SpaceBitmap* GetMarkBitmap() const = 0;
const std::string GetName() const {
return name_;
Space(const std::string& name, MemMap* mem_map, byte* begin, byte* end,
GcRetentionPolicy gc_retention_policy)
: name_(name),
gc_retention_policy_(gc_retention_policy) {}
std::string name_;
// Underlying storage of the space
UniquePtr<MemMap> mem_map_;
// The beginning of the storage for fast access (always equals mem_map_->GetAddress())
byte* const begin_;
// Current end of the space.
byte* end_;
// Garbage collection retention policy, used to figure out when we should sweep over this space.
GcRetentionPolicy gc_retention_policy_;
std::ostream& operator<<(std::ostream& os, const Space& space);
// An alloc space is a space where objects may be allocated and garbage collected.
class AllocSpace : public Space {
// Allocate num_bytes without allowing the underlying mspace to grow.
Object* AllocWithGrowth(size_t num_bytes);
// Allocate num_bytes allowing the underlying mspace to grow.
Object* AllocWithoutGrowth(size_t num_bytes);
// Return the storage space required by obj.
size_t AllocationSize(const Object* obj);
void Free(Object* ptr);
void FreeList(size_t num_ptrs, Object** ptrs);
void* MoreCore(intptr_t increment);
void* GetMspace() const {
return mspace_;
// Hands unused pages back to the system.
void Trim();
// Perform a mspace_inspect_all which calls back for each allocation chunk. The chunk may not be
// in use, indicated by num_bytes equaling zero.
void Walk(void(*callback)(void *start, void *end, size_t num_bytes, void* callback_arg),
void* arg);
// Returns the number of bytes that the heap is allowed to obtain from the system via MoreCore.
size_t GetFootprintLimit();
// Set the maximum number of bytes that the heap is allowed to obtain from the system via
// MoreCore. Note this is used to stop the mspace growing beyond the limit to Capacity. When
// allocations fail we GC before increasing the footprint limit and allowing the mspace to grow.
void SetFootprintLimit(size_t limit);
// Removes the fork time growth limit on capacity, allowing the application to allocate up to the
// maximum reserved size of the heap.
void ClearGrowthLimit() {
growth_limit_ = NonGrowthLimitCapacity();
// Override capacity so that we only return the possibly limited capacity
virtual size_t Capacity() const {
return growth_limit_;
// The total amount of memory reserved for the alloc space
virtual size_t NonGrowthLimitCapacity() const {
return mem_map_->End() - mem_map_->Begin();
virtual bool IsAllocSpace() const {
return gc_retention_policy_ != GCRP_NEVER_COLLECT;
virtual bool IsImageSpace() const {
return false;
virtual bool IsZygoteSpace() const {
return gc_retention_policy_ == GCRP_FULL_COLLECT;
virtual SpaceBitmap* GetLiveBitmap() const {
return live_bitmap_.get();
virtual SpaceBitmap* GetMarkBitmap() const {
return mark_bitmap_.get();
// Swap the live and mark bitmaps of this space. This is used by the GC for concurrent sweeping.
void SwapBitmaps();
// Turn ourself into a zygote space and return a new alloc space which has our unused memory.
AllocSpace* CreateZygoteSpace();
Object* AllocWithoutGrowthLocked(size_t num_bytes) EXCLUSIVE_LOCKS_REQUIRED(lock_);
friend class Space;
UniquePtr<SpaceBitmap> live_bitmap_;
UniquePtr<SpaceBitmap> mark_bitmap_;
static size_t bitmap_index_;
AllocSpace(const std::string& name, MemMap* mem_map, void* mspace, byte* begin, byte* end,
size_t growth_limit);
bool Init(size_t initial_size, size_t maximum_size, size_t growth_size, byte* requested_base);
static void* CreateMallocSpace(void* base, size_t morecore_start, size_t initial_size);
// The boundary tag overhead.
static const size_t kChunkOverhead = kWordSize;
// Used to ensure mutual exclusion when the allocation spaces data structures are being modified.
Mutex lock_;
// Underlying malloc space
void* const mspace_;
// The capacity of the alloc space until such time that ClearGrowthLimit is called.
// The underlying mem_map_ controls the maximum size we allow the heap to grow to. The growth
// limit is a value <= to the mem_map_ capacity used for ergonomic reasons because of the zygote.
// Prior to forking the zygote the heap will have a maximally sized mem_map_ but the growth_limit_
// will be set to a lower value. The growth_limit_ is used as the capacity of the alloc_space_,
// however, capacity normally can't vary. In the case of the growth_limit_ it can be cleared
// one time by a call to ClearGrowthLimit.
size_t growth_limit_;
// An image space is a space backed with a memory mapped image
class ImageSpace : public Space {
const ImageHeader& GetImageHeader() const {
return *reinterpret_cast<ImageHeader*>(Begin());
const std::string& GetImageFilename() const {
return name_;
// Mark the objects defined in this space in the given live bitmap
void RecordImageAllocations(SpaceBitmap* live_bitmap) const
virtual bool IsAllocSpace() const {
return false;
virtual bool IsImageSpace() const {
return true;
virtual bool IsZygoteSpace() const {
return false;
virtual SpaceBitmap* GetLiveBitmap() const {
return live_bitmap_.get();
virtual SpaceBitmap* GetMarkBitmap() const {
// ImageSpaces have the same bitmap for both live and marked. This helps reduce the number of
// special cases to test against.
return live_bitmap_.get();
friend class Space;
UniquePtr<SpaceBitmap> live_bitmap_;
static size_t bitmap_index_;
ImageSpace(const std::string& name, MemMap* mem_map);
// Callback for dlmalloc_inspect_all or mspace_inspect_all that will madvise(2) unused
// pages back to the kernel.
void MspaceMadviseCallback(void* start, void* end, size_t used_bytes, void* /*arg*/);
// Callback for the obsolete dlmalloc_walk_free_pages.
void MspaceMadviseCallback(void* start, void* end, void* /*arg*/);
} // namespace art
#endif // ART_SRC_SPACE_H_