On 10 Aug 2001 17:25:58 +1200, Bryce McKinlay wrote:
> Tom Tromey wrote:
>
> >Suppose a thread calls PushbackInputStream.read and there are no bytes
> >to be read. So the thread blocks.
> >
> >Now suppose another thread calls PushbackInputStream.unread.
> >
> >Ideally you'd expect the first thread to wake up and read the
> >pushed-back bytes. However, this doesn't happen. And in fact it
> >isn't easy to make it happen. I think you could do it by making a new
> >thread inside PushbackInputStream.read. That is awfully heavy though.
> >
> In general, I dont think its useful/safe to have more than one thread
> reading from any given InputStream, so in practise this probibly isnt a
> problem. Besides, even if there was a way to unblock another reading
> thread, there would still be consistency issues. If thread A reads a
> chunk of data, then thread B reads a chunk, then thread A decides to
> push back a byte, that byte would no longer be in the correct position
> on the stream.
>
He's not talking about two threads reading one input stream. He's
talking about the (probably common) situation where one thread is
reading the input stream and another is writing to it. I think this is
a reasonable application for PushbackInputStream.
I can't see a way out of the situation either, without creating some
kind of dual block (block on *either* the pushback or the underlying
stream) or possibly setting a time interval to periodically come back
from the underlying stream and check the pushback.
--John
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