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/*
* Copyright 2012 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef GrMemoryPool_DEFINED
#define GrMemoryPool_DEFINED
#include "GrTypes.h"
#ifdef SK_DEBUG
#include "SkTHash.h"
#endif
/**
* Allocates memory in blocks and parcels out space in the blocks for allocation
* requests. It is optimized for allocate / release speed over memory
* efficiency. The interface is designed to be used to implement operator new
* and delete overrides. All allocations are expected to be released before the
* pool's destructor is called. Allocations will be 8-byte aligned.
*/
class GrMemoryPool {
public:
/**
* Prealloc size is the amount of space to allocate at pool creation
* time and keep around until pool destruction. The min alloc size is
* the smallest allowed size of additional allocations. Both sizes are
* adjusted to ensure that:
* 1. they are are 8-byte aligned
* 2. minAllocSize >= kSmallestMinAllocSize
* 3. preallocSize >= minAllocSize
*
* Both sizes is what the pool will end up allocating from the system, and
* portions of the allocated memory is used for internal bookkeeping.
*/
GrMemoryPool(size_t preallocSize, size_t minAllocSize);
~GrMemoryPool();
/**
* Allocates memory. The memory must be freed with release().
*/
void* allocate(size_t size);
/**
* p must have been returned by allocate()
*/
void release(void* p);
/**
* Returns true if there are no unreleased allocations.
*/
bool isEmpty() const { return fTail == fHead && !fHead->fLiveCount; }
/**
* Returns the total allocated size of the GrMemoryPool minus any preallocated amount
*/
size_t size() const { return fSize; }
/**
* Returns the preallocated size of the GrMemoryPool
*/
size_t preallocSize() const { return fHead->fSize; }
/**
* Minimum value of minAllocSize constructor argument.
*/
constexpr static size_t kSmallestMinAllocSize = 1 << 10;
private:
struct BlockHeader;
static BlockHeader* CreateBlock(size_t size);
static void DeleteBlock(BlockHeader* block);
void validate();
struct BlockHeader {
#ifdef SK_DEBUG
uint32_t fBlockSentinal; ///< known value to check for bad back pointers to blocks
#endif
BlockHeader* fNext; ///< doubly-linked list of blocks.
BlockHeader* fPrev;
int fLiveCount; ///< number of outstanding allocations in the
///< block.
intptr_t fCurrPtr; ///< ptr to the start of blocks free space.
intptr_t fPrevPtr; ///< ptr to the last allocation made
size_t fFreeSize; ///< amount of free space left in the block.
size_t fSize; ///< total allocated size of the block
};
static const uint32_t kAssignedMarker = 0xCDCDCDCD;
static const uint32_t kFreedMarker = 0xEFEFEFEF;
struct AllocHeader {
#ifdef SK_DEBUG
uint32_t fSentinal; ///< known value to check for memory stomping (e.g., (CD)*)
int32_t fID; ///< ID that can be used to track down leaks by clients.
#endif
BlockHeader* fHeader; ///< pointer back to the block header in which an alloc resides
};
size_t fSize;
size_t fMinAllocSize;
BlockHeader* fHead;
BlockHeader* fTail;
#ifdef SK_DEBUG
int fAllocationCnt;
int fAllocBlockCnt;
SkTHashSet<int32_t> fAllocatedIDs;
#endif
protected:
enum {
// We assume this alignment is good enough for everybody.
kAlignment = 8,
kHeaderSize = GR_CT_ALIGN_UP(sizeof(BlockHeader), kAlignment),
kPerAllocPad = GR_CT_ALIGN_UP(sizeof(AllocHeader), kAlignment),
};
};
/**
* Variant of GrMemoryPool that can only allocate objects of a single type. It is
* not as flexible as GrMemoryPool, but it has more convenient allocate() method,
* and more importantly, it guarantees number of objects that are preallocated at
* construction or when adding a new memory block. I.e.
*
* GrMemoryPool pool(3 * sizeof(T), 1000 * sizeof(T));
* pool.allocate(sizeof(T));
* pool.allocate(sizeof(T));
* pool.allocate(sizeof(T));
*
* will preallocate 3 * sizeof(T) bytes and use some of those bytes for internal
* structures. Because of that, last allocate() call will end up allocating a new
* block of 1000 * sizeof(T) bytes. In contrast,
*
* GrObjectMemoryPool<T> pool(3, 1000);
* pool.allocate();
* pool.allocate();
* pool.allocate();
*
* guarantees to preallocate enough memory for 3 objects of sizeof(T), so last
* allocate() will use preallocated memory and won't cause allocation of a new block.
*
* Same thing is true for the second (minAlloc) ctor argument: this class guarantees
* that a newly added block will have enough space for 1000 objects of sizeof(T), while
* GrMemoryPool does not.
*/
template <class T>
class GrObjectMemoryPool: public GrMemoryPool {
public:
/**
* Preallocates memory for preallocCount objects, and sets new block size to be
* enough to hold minAllocCount objects.
*/
GrObjectMemoryPool(size_t preallocCount, size_t minAllocCount)
: GrMemoryPool(CountToSize(preallocCount),
CountToSize(SkTMax(minAllocCount, kSmallestMinAllocCount))) {
}
/**
* Allocates memory for an object, but doesn't construct or otherwise initialize it.
* The memory must be freed with release().
*/
T* allocate() { return static_cast<T*>(GrMemoryPool::allocate(sizeof(T))); }
private:
constexpr static size_t kTotalObjectSize =
kPerAllocPad + GR_CT_ALIGN_UP(sizeof(T), kAlignment);
constexpr static size_t CountToSize(size_t count) {
return kHeaderSize + count * kTotalObjectSize;
}
public:
/**
* Minimum value of minAllocCount constructor argument.
*/
constexpr static size_t kSmallestMinAllocCount =
(GrMemoryPool::kSmallestMinAllocSize - kHeaderSize + kTotalObjectSize - 1) /
kTotalObjectSize;
};
template <class T>
constexpr size_t GrObjectMemoryPool<T>::kSmallestMinAllocCount;
#endif
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