On 29/01/12 21:40, Henry Story wrote:
It would be better of course if the structure passed could be one that was
not
changeable, even better, if it could use NIO bytes buffers as that reduces
the need even to copy data, but I guess that the Jena parsers were not written
with that in mind.
This bit, I didn't follow.
Parsing, in general, needs a char stream and, for Turtle one-char look
ahead.
The parsers work from InputStreams. The RIOT parsers work from
Tokenizers, which normally work from InputStreams but it's chnagable as
its Jena code.
An InputStream is just an interface and a bit of machinary (AKA a trait)
- it can be implemented to implement over NIO buffers so a zero-copy
design is quite possible.
RIOT has PeekInputStream which could be adapted to get bytes from an NIO
buffer.
My experience is that accessing an NIO buffer byte-by-byte needs a
little care - it may not be very cheap as several checks are always done
and, while the JIT is good, the per-byte cost that can be significant.
It might be better to read out chunks (RIOT's InputStreamBuffered). It
would still be zero-copy overall - no complete copy of the source taken.
Copying is not always bad - I have tried to do faster-than-std-java
conversion of UTF-8 bytes to chars in pure code, no copy, but the
built-in decoder (which is probably native code) is still a few-% better
despite the fact it introduces a copy. CharsetDecoders work on
ByteBuffers. I don't think its possible in java to avoid a copy at the
point of bytes->chars.
Andy
