Cygwin: dsp: Fix hang on close() if another thread calls write().

fhandler_dev_dsp (OSS) has a problem that waitforallsent(), which is
called from close(), falls into infinite loop if another thread calls
write() accidentally after close(). This patch fixes the issue.

Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

winsup/cygwin/fhandler/dsp.cc

@@ -1093,6 +1093,8 @@ fhandler_dev_dsp::open (int flags, mode_t)
 
   debug_printf ("ACCMODE=%y audio_in=%d audio_out=%d, err=%d, ret=%d",
 		flags & O_ACCMODE, num_in, num_out, err, ret);
+  if (ret)
+    being_closed = false;
   return ret;
 }
 
@@ -1106,6 +1108,12 @@ fhandler_dev_dsp::_write (const void *ptr, size_t len)
   int len_s = len;
   const char *ptr_s = static_cast <const char *> (ptr);
 
+  if (being_closed)
+    {
+      set_errno (EBADF);
+      return -1;
+    }
+
   if (audio_out_)
     /* nothing to do */;
   else if (IS_WRITE ())
@@ -1207,6 +1215,7 @@ int
 fhandler_dev_dsp::close ()
 {
   debug_printf ("audio_in=%p audio_out=%p", audio_in_, audio_out_);
+  being_closed = true;
   close_audio_in ();
   close_audio_out ();
   return fhandler_base::close ();

winsup/cygwin/local_includes/fhandler.h

@@ -2762,6 +2762,7 @@ class fhandler_dev_dsp: public fhandler_base
   int audiochannels_;
   Audio_out *audio_out_;
   Audio_in  *audio_in_;
+  bool being_closed;
  public:
   fhandler_dev_dsp ();
   fhandler_dev_dsp *base () const {return (fhandler_dev_dsp *)archetype;}