time for 1.5.11?

Igor Pechtchanski pechtcha@cs.nyu.edu
Thu Jun 10 00:56:00 GMT 2004


On Wed, 9 Jun 2004, Christopher Faylor wrote:

> On Wed, Jun 09, 2004 at 04:28:37PM -0400, Igor Pechtchanski wrote:
> >On Wed, 9 Jun 2004, Igor Pechtchanski wrote:
> >
> >> On Wed, 9 Jun 2004, Corinna Vinschen wrote:
> >>
> >> > On Jun  9 13:01, Christopher Faylor wrote:
> >> > > Anyway, on to the future...  Would it make sense to release a 1.5.11?
> >> > > Do you think we've hit all of the fallout from the path reorg/speedup?
> >> >
> >> > Looking through the reports on the Cygwin list, I see that we never
> >> > got a reply if the MapViewOfFileEx problem has been solved.  Also,
> >> > what about the report that /dev/dsp isn't working?  Igor was going to
> >> > investigate this further.  Any news, Igor?
> >>
> >> I'm still investigating.  So far it looks like /dev/dsp doesn't like to be
> >> dup'd (but then, who does? ;-)).  I'm attaching a short test program to
> >> demostrate this, but I'll keep digging...
> >
> >...And moments after I sent the above I found the culprit (I think).
> >Seems like fhandler_dsp::dup() neglects to call fhandler_base::dup(), so
> >the IO handle is unset.  It should be a trivial 1-line patch, but just in
> >case, can someone with a copyright assignment take care of this?
>
> You should be safe if it is really a one line patch.  Don't you want to
> get your name into the Cygwin changelog limelight?
>
> cgf

Ok, it turns out that to fix this properly, we'll need a much larger patch
than the one line I was looking at...  Here are some thoughts.

First off, my guess above was wrong.  The IO handle has nothing to do with
this -- fhandler_dev_dsp doesn't use it.  However, the intuition (I still
think) was correct: some fields, namely the audio_in_ and audio_out_
pointers, weren't replicated on dup(), so the new (duped) object ended up
with NULL fields, and couldn't write to them.

The simplest solution to the above is to simply copy the pointers.  This
will work for the test program I provided earlier, but won't for another
legitimate test program (attached) that closes the original handle before
using the duped one (I think this behavior is allowed).

The "proper" way to fix this, IMO, would be to allow sharing the audio_in_
and audio_out_ objects, and have some sort of reference count in them,
instead of deleting them outright in close().  I'm not sure this will
cover the situations when a process is spawned (e.g., fork), but it should
suffice for redirection.  This, however, promises to be a non-trivial
patch.

Comments?
	Igor
-- 
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-------------- next part --------------
#include <fcntl.h>
#include <unistd.h>

#define BUFSIZE	1024
#define WORKS	"This works\n"
#define NWORKS	"This doesn\'t work\n"

int main(int ac, char *av[]) {
  char buf[BUFSIZE+1];
  int num, src, dst;

  write(2, WORKS, sizeof(WORKS)-1);
  src = open("/cygdrive/c/WINNT/Media/tada.wav", O_RDONLY);
  dst = open("/dev/dsp", 0x601);
  while ((num = read(src, buf, BUFSIZE)) > 0)
    write(dst, buf, num);
  close(dst);
  close(src);

  write(2, NWORKS, sizeof(NWORKS)-1);
  src = open("/cygdrive/c/WINNT/Media/tada.wav", O_RDONLY);
  dst = open("/dev/dsp", 0x601);
  if (dup2(dst, 1) != -1) {
    close(dst);
    dst = 1;
    while ((num = read(src, buf, BUFSIZE)) > 0)
      write(dst, buf, num);
  }
  close(dst);
  close(src);
}



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