Re: [example] how to get popen2() working? [XP, MSVC 2.9.15-octave]

[andreas.naessl]

> Basically, your problem comes from the fact that the streams you get
> back from popen2 are in non-blocking mode and that once an error
> occured on the read end, you need to clear its state to be able to read
> again. When you put your code into a m-file, you should
> 1) use fflush after writing something in the write-end, to be sure the data
> arrived to the child process
> 2) maybe wait a little bit before trying to read something on the read-end,
> to be sure the child process has processed the data and answered back;
> if an error occured, use fclear to clear the stream state
> 
> Alternatively, you can use an (apparently) undocumented feature of the
> popen2 function: you can provide a 3rd argument to specify the pipe mode;
> if true, the pipes are blocking, if false (the default), the pipes are
> non-blocking.
> In non-blocking mode, be aware that you may block octave if there's nothing
> to read on the read-end.
> 
> Michael.
> _______________________________________________
> Help-octave mailing list
> address@hidden
> https://www.cae.wisc.edu/mailman/listinfo/help-octave


hello. below is my m-file code, things are working now with my example.

But i stll don't understand, why the popen2-help-example (the "sort -r")
doesn't work. i played a bit around, but it didn't do...
i have the feeling the "sort" behaviour might be the reason... 
at oct-promt with: system('sort -r') i need to type a final "ctrl-D" 
after the inputlines to get my sorted results back -
do we send it in the popen2-example? 

andreas

----
# testprogramm kommunikation mit python server-programm via pipe popen2
0;

function r=snd(fid,s);
  r=fputs(fid,[s,"\n"]);  # newline for string added here
  fflush(fid);
endfunction

function r=rcv(fid);
  while (ischar(r=fgets(fid)) == false)    
    fclear(fid);   # endless loop; i'm shure there comes sth. to read otherwise 
hang up
  endwhile         # maybe implement later to jump out when waiting too long 
for a reply
endfunction

[a,b,i]=popen2('python','svr_02.py');

snd(a,"testcmd 1"); 
rcv(b)                  # get back echo 
snd(a,"testcmd 2"); 
rcv(b)                  # get back echo
snd(a,"0");             # "0" = shutdown server-prg 
rcv(b)

fclose(a);
fclose(b);