Re: Data available for reading in a GIOChannel

[Paul Davis <paul linuxaudiosystems com>]

On Mon, 2007-05-28 at 17:26 +0200, Jonathan Winterflood wrote:
> Hi,
> 
> > you never know how much readable data is available until you read
> it, you are only ever guaranteed to have one byte of data available
> for reading anyway.
> 
> In my opinion, the channel should _always_ know how much data is
> available, how can it tell that there is nothing there?... Plus, it
> can't not know the amount of data it _has_ actually recieved and is
> buffered ready for me... 

there is a very big difference between knowing the distinctions between:
 
   * something and nothing
   * specifically how much and nothing at all

the process that leads to the callback is called as soon as a single
byte of data arrives. there might be more data by the time it actually
executes. nothing else in the system (except perhaps a device driver) is
buffering data for you and then saying (post-facto) "we have some
stuff". your callback can do that if it wants to offer that kind of
service to high level layers of your application/code.

> Java InputStreams for example have the available() method:
> http://java.sun.com/javase/6/docs/api/java/io/InputStream.html#available()

thats because Java InputStreams are heavily buffered. glib/gtk
IOChannels are not, by default. in particular, when you use this
callback method, your code is being notified that there is data
available long before a Java InputStream would have told that it had
information ready.

> > [...] I read the data in 1024 byte chunks [...]
> This sounds like a good workaround, which will work well in a watch
> callback; I'll use that

the important thing is just to use non-blocking I/O with the channel. t