ByteBuffer pooling and reuse

[lbensaad]

I want to use flatbuffers with a ByteBuffer pooler or reuse an existing ByteBuffer, so it will be nice if add a constructor to the FlatBufferBuilder that accepts a ByteBuffer as parameter.

[ghost]

Agreed, sounds like a good feature.

[lbensaad]

Good, especially if this library is described as "Memory Efficient Serialization Library" so adding this feature should be a core feature, I also plan to use it with Netty which use pooling also.
It could be something like this:
public FlatBufferBuilder(ByteBuffer bb)
{
this.bb = bb;
this.bb.order(ByteOrder.LITTLE_ENDIAN);
space=this.bb.position();
}

[ghost]

why space=this.bb.position() ? FlatBuffers writes to ByteBuffers in an absolute way, and does not rely on position() being anywhere in particular. space represents the amount of space left over at the beginning of the buffer, so should be set to the size of the backing array at the start.

[ghost]

Just added such a constructor as part of the last commit.

[lbensaad]

That is good, thank you,

[lbensaad]

I see that you clear the Buffer before using it, what if the buffer contains other data? But i don't know if this is a possible scenario!

[ghost]

the clear() call only resets the writable area, it doesn't actually clear
the bytes. But yes, to create a FlatBuffer, you want to be using the entire
ByteBuffer, concatenating isn't supported.

[lbensaad]

I think there is another problem with direct buffers, they don't have array(), and the FlatBufferBuilder uses it a lot so it will cause a problem.
I think you should throw UnsuportedOperationException if the the provided buffer has no array (make a call to hasArray() to know that)

[ghost]

ok, will add that.

[lbensaad]

1. It could be a better solution to use bb.capacity() instead of dd.array().length; I did a Replace All in my code editor and test it and it did work, you can do more testing.
2. You should also avoid the use of bb.array() and System.arrayCopy like in fbb.growByteBuffer() and fbb.createString. You should use bb.put(byte[]) and bb.get(byte[]) instead.
3. i think growByteBuffer() and newByteBuffer() should be static functions.

[ghost]

1. I already did that.
2. The reason I didn't use put and get is that there are no absolute versions of those calls available, meaning you need to explicitly set the position.. though I suppose that is no big deal.
3. Agreed.