[ECOS] Starvation in cyg_libc_stdio_flush_all_but()?

Robin Farine acnrf@dial.eunet.ch
Mon Dec 3 08:57:00 GMT 2001


Unfortunately, this test already appears in my sources. Thanks anyway for
your answer.

Robin

"David Airlie" <David.Airlie@parthus.com> writes:

> I think I had something like this fixed by
> 
> diff -u -r1.1 -r1.2
> --- ecos/packages/language/c/libc/stdio/current/src/common/fflush.cxx	2001/04/19 16:06:09	1.1
> +++ ecos/packages/language/c/libc/stdio/current/src/common/fflush.cxx	2001/12/03 15:27:25	1.2
> @@ -86,7 +86,10 @@
>                  } // if
>                  else {
>                      // valid stream
> -
> +#ifdef CYGSEM_LIBC_STDIO_WANT_BUFFERED_IO
> +		  if(!stream->flags.last_buffer_op_was_read)
> +#endif
> +		  {
>                      if ( stream->trylock_me() ) {
>                          err = stream->flush_output_unlocked();
>                          stream->unlock_me();
> @@ -94,6 +97,7 @@
>                      } // if
>                      else
>                          loop_again = true;
> +		  }
>                  } // else
>              } // if
>          } // for
> 
> this is in CVS at the time I found it in my tree.. so I just stole the fix
> from CVS..
> 
> let me know if it works..
> 
> Dave.
> 
> On 3 Dec 2001, Robin Farine wrote:
> 
> > Hi,
> >
> > Under some circumstances, my application's UI freezes but background threads
> > still run. The following scenario causes it to happen:
> >
> >   1. Two threads; one, called CLI, handles the command line interface. The
> >      second, say WRK, does some work and prints messages to the console.
> >
> >   2. priority(CLI) > priority(WRK)    (higher priority, not higher value)
> >
> >   3. While WRK is printing a message to stdout, the user hits RETURN which
> >      causes the CLI thread to wake up and display a prompt to stderr. This ends
> >      in cyg_libc_stdio_flush_all_but() with the CLI thread looping endlessly
> >      trying to flush stdout since WRK owns stdout stream's lock and cannot
> >      release it because of its lower priority.
> >
> > Did anyone already have this problem? Do the current CVS sources fix it?
> >
> >
> > Thanks,
> >
> > Robin
> >
> 
> -- 
>       David Airlie, Software Engineer, Parthus Technologies plc.,
>        Mary Rosse Centre, National Tech Park, Limerick, Ireland.
>    t: +353-61-508116 / f: +353-61-508101 / David.Airlie@parthus.com



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