Re: Event loop and http::geturl

* Christian Gollwitzer <auriocus@gmx.de>
| Am 26.06.25 um 23:02 schrieb et99:
| > I wonder, if you are reading a file that is being written from
| > another process, sort of like a "tail" program, doesn't tcl's
| > [fileevent
| > <channel> readable <script>] trigger constantly? Isn't this in
| > effect a tight polling loop?

>

| The underlying mechanism is select() or poll(). To my knowledge, this
| only works for pipes/sockets, not for files.

select() also works for files, the effect is that it indeed triggers
immediately on each call.

     man select(2)
     [...]
       readfds
              The file descriptors in this set are watched to see if they  are
              ready  for reading.
          **  A file descriptor is ready for reading if a read operation will not block;
              in particular, a file  descriptor is also ready on end-of-file.

(** emphasis by me).

The effect in TCL of setting a readable-fileevent on a regular disk file
is indeed that the event fires repeatedly until EOF, blocking any GUI
updates which would run "after idle".

R'