[Octave-bug-tracker] [bug #33330] fgets hangs octave when reading newline

[Rik]

Follow-up Comment #5, bug #33330 (project octave):

The 'hang' is not really a hang.  When you do a read on a socket and there is
nothing available the operating system has two choices.  The default is
blocking I/O which means the process stops and waits for input.  For example,
when you call zenity from a bash command line it stops and waits for you to do
something with the graphical object.  It doesn't just return to the prompt and
allow you to continue typing.  Octave is operating the same way.  If you must,
you can tell the operating system that you want non-blocking I/O in which case
any call to read something from the socket will return immediately if there is
nothing there.  However, you shouldn't build this into a tight polling loop. 
Don't try something like the loop below.


while (isempty (fscanf (fid, '%s', 'C')))
  sleep (1);
endwhile


If you do need to change to non-blocking mode you can use the fcntl() function
like so


fcntl (fid, F_SETFL, O_NONBLOCK);


in which case a read on an empty socket will return [] immediately.


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