[Ecls-list] Potential problem with streams and EXT:RUN-PROGRAM

Juan Jose Garcia Ripoll jlr at mpq.mpg.de
Wed May 18 07:04:41 UTC 2005

Goffioul Michael wrote:

>During a few days, I fought with a problem I had with my matlab-embedded-ECL: the
>symptom was a stream error after a call to EXT:RUN-PROGRAM, but it often happen
>in an unpredictable way.
>Looking at the code of that function, I realized that the standard handles are
>duplicated, but this doesn't take into account the actual value of the variables
>*standard-input/output* and the like. This means that if you redefine the LISP
>standard input/outputs (which is my case), ext:run-program doesn't take that into
>In my particular case, the problem was that :error is T by default, such that the
>child program got a duplicated handle of stderr. In the context of MATLAB, writing
>to that handle produced errors (it's still unclear why this happen).
With current fixes EXT:RUN-PROGRAM inspects the variables 
*STANDARD-INPUT/OUTPUT* and *ERROR-OUTPUT* to decide what handles the 
children processes should get. If you want the child's error output to 
be discarded, it should suffice to set *ERROR-OUTPUT* to some stupid 
value, which is not a valid file, or, as you noticed, passing a value of 
:ERROR NIL to the routine EXT:RUN-PROGRAM.

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