PxcScratchAllocator.h

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#ifndef PXC_SCRATCH_ALLOCATOR_H
#define PXC_SCRATCH_ALLOCATOR_H
 
#include "foundation/PxAssert.h"
#include "PxvConfig.h"
#include "foundation/PxMutex.h"
#include "foundation/PxArray.h"
#include "foundation/PxAllocator.h"
#include "foundation/PxUserAllocated.h"
 
namespace physx
{
class PxcScratchAllocator : public PxUserAllocated
{
    PX_NOCOPY(PxcScratchAllocator)
public:
    PxcScratchAllocator() : mStack("PxcScratchAllocator"), mStart(NULL), mSize(0)
    {
        mStack.reserve(64);
        mStack.pushBack(0);
    }
 
    void setBlock(void* addr, PxU32 size)
    {
        PX_ASSERT(!(size&15));
 
        // if the stack is not empty then some scratch memory was not freed on the previous frame. That's 
        // likely indicative of a problem, because when the scratch block is too small the memory will have
        // come from the heap
 
        PX_ASSERT(mStack.size()==1);
        mStack.popBack();
 
        mStart = reinterpret_cast<PxU8*>(addr);
        mSize = size;
        mStack.pushBack(mStart + size);
    }
 
    void* allocAll(PxU32& size)
    {
        PxMutex::ScopedLock lock(mLock);
        PX_ASSERT(mStack.size()>0);
        size = PxU32(mStack.back()-mStart);
 
        if(size==0)
            return NULL;
 
        mStack.pushBack(mStart);
        return mStart;
    }
 
    void* alloc(PxU32 requestedSize, bool fallBackToHeap = false)
    {
        requestedSize = (requestedSize+15)&~15;
 
        PxMutex::ScopedLock lock(mLock);
        PX_ASSERT(mStack.size()>=1);
 
        PxU8* top = mStack.back();
 
        if(top - mStart >= ptrdiff_t(requestedSize))
        {
            PxU8* addr = top - requestedSize;
            mStack.pushBack(addr);
            return addr;
        }
 
        if(!fallBackToHeap)
            return NULL;
 
        return PX_ALLOC(requestedSize, "Scratch Block Fallback");
    }
 
    void free(void* addr)
    {
        PX_ASSERT(addr!=NULL);
        if(!isScratchAddr(addr))
        {
            PX_FREE(addr);
            return;
        }
 
        PxMutex::ScopedLock lock(mLock);
        PX_ASSERT(mStack.size()>1);
 
        PxU32 i=mStack.size()-1;        
        while(mStack[i]<addr)
            i--;
 
        PX_ASSERT(mStack[i]==addr);
        mStack.remove(i);
    }
 
    bool isScratchAddr(void* addr) const
    {
        PxU8* a = reinterpret_cast<PxU8*>(addr);
        return a>= mStart && a<mStart+mSize;
    }
 
private:
    PxMutex             mLock;
    PxArray<PxU8*>      mStack;
    PxU8*               mStart;
    PxU32               mSize;
};
 
}
 
#endif