[ET Trac] [Einstein Toolkit] #1704: redirect stdout and stderr of all processes if requested (also of the root process)

[Einstein Toolkit]

#1704: redirect stdout and stderr of all processes if requested (also of the root
process)
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  Reporter:  knarf        |       Owner:                     
      Type:  enhancement  |      Status:  reopened           
  Priority:  optional     |   Milestone:                     
 Component:  Cactus       |     Version:  development version
Resolution:               |    Keywords:                     
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Comment (by knarf):

 What I intended was having Cactus write to a file _and_ to the screen.
 However, after reading up on the matter a bit more that does not seem
 possible, at least not using the mechanism Cactus uses for redirection.

 Cactus uses freopen, which essentially changes stdout and/or stderr to
 point to a file. There does not seem to be a way to have one input stream
 point to two outputs. One would need to write twice. This is problematic
 in this case, as I would imagine not everyone uses the CCTK_* wrappers,
 especially not for debugging. The current solution redirects, e.g., a
 printf too. Even worse - freopen is not (portably) reversible. Once
 redirected to a file there is no (portable) way to get it back to stdout.

 One option I still see would be to redirect to a file, and having a second
 thread (created before MPI_Init, like the web server) constantly printing
 the contents of that file (like tail -f). This would not be ideal either
 though, because especially for crashes (one of the use-cases of this
 feature), users might 'miss' output.

 Another possibility would indeed be a new parameter to do the normal
 redirection also on the root process, but one would need to know then that
 this run will be quite silent in the terminal...

 Does anybody have a better idea? Any preferences?

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/1704#comment:6>
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