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/*
* 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"
// Used by SkSmallAllocator to call the destructor for objects it has
// allocated.
template<typename T> void destroyT(void* ptr) {
static_cast<T*>(ptr)->~T();
}
/*
* 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 NULL.
* 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.
*/
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 NULL.
sk_free(rec->fHeapStorage);
}
}
/*
* Create a new object of type T. Its lifetime will be handled by this
* SkSmallAllocator.
* Each version behaves the same but takes a different number of
* arguments.
* Note: If kMaxObjects have been created by this SkSmallAllocator, NULL
* will be returned.
*/
template<typename T>
T* createT() {
void* buf = this->reserveT<T>();
if (NULL == buf) {
return NULL;
}
SkNEW_PLACEMENT(buf, T);
return static_cast<T*>(buf);
}
template<typename T, typename A1> T* createT(const A1& a1) {
void* buf = this->reserveT<T>();
if (NULL == buf) {
return NULL;
}
SkNEW_PLACEMENT_ARGS(buf, T, (a1));
return static_cast<T*>(buf);
}
template<typename T, typename A1, typename A2>
T* createT(const A1& a1, const A2& a2) {
void* buf = this->reserveT<T>();
if (NULL == buf) {
return NULL;
}
SkNEW_PLACEMENT_ARGS(buf, T, (a1, a2));
return static_cast<T*>(buf);
}
template<typename T, typename A1, typename A2, typename A3>
T* createT(const A1& a1, const A2& a2, const A3& a3) {
void* buf = this->reserveT<T>();
if (NULL == buf) {
return NULL;
}
SkNEW_PLACEMENT_ARGS(buf, T, (a1, a2, a3));
return static_cast<T*>(buf);
}
/*
* 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 NULL;
}
const size_t storageRemaining = SkAlign4(kTotalBytes) - fStorageUsed;
storageRequired = SkAlign4(storageRequired);
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 = NULL;
SkASSERT(SkIsAlign4(fStorageUsed));
rec->fObj = static_cast<void*>(fStorage + (fStorageUsed / 4));
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*);
};
// Number of bytes used so far.
size_t fStorageUsed;
// Pad the storage size to be 4-byte aligned.
uint32_t fStorage[SkAlign4(kTotalBytes) >> 2];
uint32_t fNumObjects;
Rec fRecs[kMaxObjects];
};
#endif // SkSmallAllocator_DEFINED
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