Tcl question: fileevent: Does it block?

[Roger Oberholtzer]

How about: http://www.rolf-schroedter.de/moni/moni.html

It is a rather nice serial port monitor.

What type of channel are you reading from? How did you set up
fconfigure?

fileevent is not so much blocking as the read or write you are doing. 


On Wed, 2003-12-31 at 21:04, Joel Hammer wrote:
> Can you point me to some simple script samples on the internet which
> use fileevent?  I really need to find out why fileevent in my hands blocks.
> 
> Thanks
> 
> Joel
> 
> On Wed, Dec 31, 2003 at 01:18:06PM +0100, Roger Oberholtzer wrote:
> > fileevent, by nature, should be non-blocking. That is, it is usually set
> > up so that the code is only called when there is the requested activity
> > on the channel However, once in the fileevent handler, you can do
> > whatever you want, including trying to read more than is there or
> > writing when the output channel is full. How the channel acts depends on
> > you set it up with 'fconfigure'. 
> > 
> > On Wed, 2003-12-31 at 02:07, Joel Hammer wrote:
> > > Rank beginner here.
> > > 
> > > >From reading the documentation of fileevent, I got the impression it
> > > simply registers a procedure with a file event and then the script moves
> > > on. That isn't my experience.
> > > 
> > > This little snippet hangs at the fileevent line if there is no input in
> > > the pipe.  Once there is something to read in the pipe, the SomeProcedure
> > > is called and processing of the script moves to the puts line after
> > > the fileevent line. Additional input to the pipe is ignored. This is
> > > like nothing I expected from reading the documentation. It makes the
> > > fileevent command no better than a while loop.
> > > 
> > > BTW, I load the pipe with echo commands from another terminal.
> > > 
> > > Any insight appreciated.
> > > 
> > > Joel
> > > 
> > > #!/etc/alternatives/wish -f
> > > set i 0
> > > set  id [ open /tmp/NewPipe r ]
> > > fileevent $id readable [list SomeProcedure $id]
> > > puts "beyond  filevent" 
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