fredag 6 juli 2012

Byte off more than one can buffer

This is more of a mental note to self. But it gives a small insight to what I'm battling with.

I've just traced in which way VMNetChannel allocates its ByteBuffer (ByteBuffers are used for pretty much anything handling data, not only network stuff, so its a pretty crucial thing to have).
Starting in VMNetChannel, we find a ByteBuffer.allocate(int capacity). It goes something like this:

  1. ByteBuffer.allocate(capacity) calls
  2. DirectByteBufferImpl.allocate(capactiy) calls
  3. DirectByteBufferImpl.ReadWrite(capacity) ReadWrite is an internal class which calls:
  4. ReadWrite constructor calling its super constructor:
  5. DirectByteBufferImpl(cap) yep, ReadWrite extends DirectByteBufferImpl
  6. DirectByteBufferImpl constructor calls its super (back to ByteBuffer) with a few arguments:
  7. ByteBuffer(capacity, capacity, 0, -1, VMDirectByteBuffer.allocate(capacity), null, 0) which passes on to its super, Buffer
  8. Buffer(capacity, capacity, 0, -1, VMDirectByteBuffer.allocate(capacity), null, 0)
And there we have it!

VMDirectByteBuffer.allocate(capacity) is native call in javanio.library, and actually does something else than throwing itself back and forth.
VMDirectByteBuffer.allocate() returns a Pointer which will be stored in Buffer().

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