| /* |
| * Copyright 2014 Google, Inc |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #ifndef SkSmallAllocator_DEFINED |
| #define SkSmallAllocator_DEFINED |
| |
| #include "SkTDArray.h" |
| #include "SkTypes.h" |
| |
| #include <new> |
| |
| /* |
| * Template class for allocating small objects without additional heap memory |
| * allocations. kMaxObjects is a hard limit on the number of objects that can |
| * be allocated using this class. After that, attempts to create more objects |
| * with this class will assert and return nullptr. |
| * |
| * kTotalBytes is the total number of bytes provided for storage for all |
| * objects created by this allocator. If an object to be created is larger |
| * than the storage (minus storage already used), it will be allocated on the |
| * heap. This class's destructor will handle calling the destructor for each |
| * object it allocated and freeing its memory. |
| * |
| * Current the class always aligns each allocation to 16-bytes to be safe, but future |
| * may reduce this to only the alignment that is required per alloc. |
| */ |
| template<uint32_t kMaxObjects, size_t kTotalBytes> |
| class SkSmallAllocator : SkNoncopyable { |
| public: |
| SkSmallAllocator() |
| : fStorageUsed(0) |
| , fNumObjects(0) |
| {} |
| |
| ~SkSmallAllocator() { |
| // Destruct in reverse order, in case an earlier object points to a |
| // later object. |
| while (fNumObjects > 0) { |
| fNumObjects--; |
| Rec* rec = &fRecs[fNumObjects]; |
| rec->fKillProc(rec->fObj); |
| // Safe to do if fObj is in fStorage, since fHeapStorage will |
| // point to nullptr. |
| sk_free(rec->fHeapStorage); |
| } |
| } |
| |
| /* |
| * Create a new object of type T. Its lifetime will be handled by this |
| * SkSmallAllocator. |
| * Note: If kMaxObjects have been created by this SkSmallAllocator, nullptr |
| * will be returned. |
| */ |
| template<typename T, typename... Args> |
| T* createT(const Args&... args) { |
| void* buf = this->reserveT<T>(); |
| if (nullptr == buf) { |
| return nullptr; |
| } |
| return new (buf) T(args...); |
| } |
| |
| /* |
| * Reserve a specified amount of space (must be enough space for one T). |
| * The space will be in fStorage if there is room, or on the heap otherwise. |
| * Either way, this class will call ~T() in its destructor and free the heap |
| * allocation if necessary. |
| * Unlike createT(), this method will not call the constructor of T. |
| */ |
| template<typename T> void* reserveT(size_t storageRequired = sizeof(T)) { |
| SkASSERT(fNumObjects < kMaxObjects); |
| SkASSERT(storageRequired >= sizeof(T)); |
| if (kMaxObjects == fNumObjects) { |
| return nullptr; |
| } |
| const size_t storageRemaining = sizeof(fStorage) - fStorageUsed; |
| Rec* rec = &fRecs[fNumObjects]; |
| if (storageRequired > storageRemaining) { |
| // Allocate on the heap. Ideally we want to avoid this situation, |
| // but we're not sure we can catch all callers, so handle it but |
| // assert false in debug mode. |
| SkASSERT(false); |
| rec->fStorageSize = 0; |
| rec->fHeapStorage = sk_malloc_throw(storageRequired); |
| rec->fObj = static_cast<void*>(rec->fHeapStorage); |
| } else { |
| // There is space in fStorage. |
| rec->fStorageSize = storageRequired; |
| rec->fHeapStorage = nullptr; |
| rec->fObj = static_cast<void*>(fStorage.fBytes + fStorageUsed); |
| fStorageUsed += storageRequired; |
| } |
| rec->fKillProc = DestroyT<T>; |
| fNumObjects++; |
| return rec->fObj; |
| } |
| |
| /* |
| * Free the memory reserved last without calling the destructor. |
| * Can be used in a nested way, i.e. after reserving A and B, calling |
| * freeLast once will free B and calling it again will free A. |
| */ |
| void freeLast() { |
| SkASSERT(fNumObjects > 0); |
| Rec* rec = &fRecs[fNumObjects - 1]; |
| sk_free(rec->fHeapStorage); |
| fStorageUsed -= rec->fStorageSize; |
| |
| fNumObjects--; |
| } |
| |
| private: |
| struct Rec { |
| size_t fStorageSize; // 0 if allocated on heap |
| void* fObj; |
| void* fHeapStorage; |
| void (*fKillProc)(void*); |
| }; |
| |
| // Used to call the destructor for allocated objects. |
| template<typename T> |
| static void DestroyT(void* ptr) { |
| static_cast<T*>(ptr)->~T(); |
| } |
| |
| struct SK_STRUCT_ALIGN(16) Storage { |
| // we add kMaxObjects * 15 to account for the worst-case slop, where each allocation wasted |
| // 15 bytes (due to forcing each to be 16-byte aligned) |
| char fBytes[kTotalBytes + kMaxObjects * 15]; |
| }; |
| |
| Storage fStorage; |
| // Number of bytes used so far. |
| size_t fStorageUsed; |
| uint32_t fNumObjects; |
| Rec fRecs[kMaxObjects]; |
| }; |
| |
| #endif // SkSmallAllocator_DEFINED |