[haiku-development] Re: A true streaming equivalent of BDataIO
- From: "Axel Dörfler" <axeld@xxxxxxxxxxxxxxxx>
- To: haiku-development@xxxxxxxxxxxxx
- Date: Tue, 17 Aug 2010 09:52:18 +0200
Christopher Humphries <redeye4@xxxxxxxxx> wrote:
> However many plug-ins insist on seekable content by accepting only a
> BPositionIO.
Which is unfortunate, but it might be fixable for some add-ons, too.
> The closest solution to the streaming data construct is the
> BBufferIO, which allows the buffering of data, but AFAIK it's missing
> the
> crucial freeing part: freeing already read data, and avoiding using
> too much
> memory in the process.
You obviously misunderstand this class. It has a fixed buffer, and will
only use that one; therefore it can only seek if the underlying class
can seek, and it will not use much memory (only as much as you tell it
to use).
> I tried writing my own subclass, where the readat function would
> return an
> equivalent number of blocks from the disk, but I think the producer
> should
> really be independent from the consumer in this kind of data
> interface.
I don't understand what you mean here.
> Now, I think that a class inheriting BPositionIO that directly
> implements
> the standard iostream class, with the general read and write
> function, but
> with little or no actual seeking capacity, should do the job. However
> I
> could be wrong...
The only way to make it work this way would be to have more than one
connection unless you want to waste lots of memory. And seeking would
be dead slow, too, as you would need to "ignore" the whole data stream.
Assume you are streaming a 4 GB HD video over the network. Now, the
reader checks some chunk at the end of the file -- do you really intend
to stream the whole 4 GB over the network to allow this? And do you,
beyond that, also intend to temporarily store the 4 GB on your local
disk in order to provide seeking capability?
Well, it cannot work this way generally, only for small files it would
be acceptable.
The only way to make it work reliable is to fix the readers. They should
as much as possible try to use a BDataIO only, and do additional checks
only if there is a BPositionIO.
In the end, there is not much point in trying to stream a format that
is not made for streaming at all, so why should we support this?
Bye,
Axel.
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