对象池似乎正在返回对象副本，而不是对象引用

Question

I have written a simple object pool manager to dish out vertex buffers wrapped in a very simple class on demand. Everything works OK except that it seems the objects being returned are being copied somehow rather than referenced, as memory use goes up unexpectedly. All the objects in the pool are instantiated at runtime in a bog standard list. This is the initializer code:

 public static void InitVBPoolManager()
    {
        int i;

        // INIT POOL VB OBJECT LIST
        VBPool = new List<PoolManagerVBObject>();            
        VBPool.Capacity = POOL_CAPACITY;

        // INIT POOL INDEX POINTERS
        nextItemIndex = 0;

        // FILL POOLMANAGER WITH INITIAL BATCH OF VBO
        for (i = 0; i < POOL_CAPACITY; ++i)
        {
            VBPool.Add(new PoolManagerVBObject(VERTEX_BUFFER_SIZE,0));
        } 
    }

This is the Get Object method:

 public static PoolManagerVBObject GetVB()
    { 
        // RETURN POOL VB
        if (nextItemIndex < POOL_CAPACITY)
        {
            VBRecycled++;
            return VBPool[nextItemIndex++];
        }
        else                
            {
                VBPool.Add(new PoolManagerVBObject(VERTEX_BUFFER_SIZE,0));
                POOL_CAPACITY++;
                VBCreated++;
                return VBPool[nextItemIndex++];
            }          
    }

And finally the code that uses the objects:

for (j = 0; j < limit; ++j)
{
   if (thisChunk.voxelVB.Count <= j)
   {   
       thisChunk.voxelVB.Add(VBPoolManager.GetVB());
   }

It seems like when GetVB() is called the returned object is having a copied made as ~260MB of RAM is eaten up. This obviously should not happen as the objects are already created in the PoolManager. If I replace the GetVB() call with just a new object() the memory consumption is the same, which is why I am led to believe the copy is being made. Anyone got any ideas ?

Answer 1

This implementation will always leak memory. You never remove references from the pool, and you never return objects to the pool.

A correctly implemented object pool would only hold references to available objects. When an object is retrieved from the pool, it shouldn't be referenced by it anymore. This way the objects can be garbage collected in case they are not returned to the pool. This points to another problem - you don't seem to have any way to return objects to the pool.

Also, your pool is not thread safe.

If you want to see how to implement an object pool correctly, you can check the Roslyn ObjectPool

Answer 2

This is the dispose method of pool manager code :

 public static void DestroyVB(PoolManagerVBObject PvbObject)
    {
         VBPool[--nextItemIndex] = PvbObject;
    }

And this is what calls it :

private static void ClearChunkVB(Vector2 PchunkXZ)
{
        VBContainer thisChunk;
        int j;

        thisChunk = Landscape.chunkVB[(int)PchunkXZ.X, (int)PchunkXZ.Y];

        if (thisChunk.voxelVB.Count > 0)
        {
            for (j = 0; j < thisChunk.voxelVB.Count; ++j)
            {
                thisChunk.voxelVB[j].VertCount = 0;
                VBPoolManager.DestroyVB(thisChunk.voxelVB[j]);
            }

            thisChunk.voxelVB.Clear();
        }
}