[newlib-cygwin] Cygwin: serial: select: simplify peek_serial

[Corinna Vinschen]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=9e106db0adb74cda86e69a3405f20955e6fc5602

commit 9e106db0adb74cda86e69a3405f20955e6fc5602
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Tue Mar 17 17:24:56 2020 +0100

    Cygwin: serial: select: simplify peek_serial
    
    - Don't use ev member for ClearCommError and WaitCommEvent.
      Both returned values are different (error value vs. event
      code).  The values are not used elsewhere so it doesn't make
      sense to store them in the object.
    
    - Drop local variable ready which is used inconsequentially.
    
    - Since WFSO already waits 10 ms, don't wait again if no char
      is in the inbound queue.
    
    - Avoid else if chains.
    
    - Only print one line of debug output on error.
    
    - Drop overlapped_armed < 0 check.  This value is only set in
      fhandler_serial::raw_read if VTIME > 0, and even then it's only
      set to be immediately reset to 0 before calling ReadFile.  So
      overlapped_armed is never actually < 0 when calling select.
    
    - Fix a screwed up statement order.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/select.cc | 43 +++++++++++++++++++------------------------
 1 file changed, 19 insertions(+), 24 deletions(-)

diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc
index 3965cfbb4..6ffc97b37 100644
--- a/winsup/cygwin/select.cc
+++ b/winsup/cygwin/select.cc
@@ -1440,23 +1440,23 @@ static int
 peek_serial (select_record *s, bool)
 {
   COMSTAT st;
+  DWORD event, io_err;
 
   fhandler_serial *fh = (fhandler_serial *) s->fh;
 
-  if (fh->get_readahead_valid () || fh->overlapped_armed < 0)
+  if (fh->get_readahead_valid ())
     return s->read_ready = true;
 
   select_printf ("fh->overlapped_armed %d", fh->overlapped_armed);
 
   HANDLE h;
   set_handle_or_return_if_not_open (h, s);
-  int ready = 0;
 
-  if ((s->read_selected && s->read_ready) || (s->write_selected && s->write_ready))
+  if ((s->read_selected && s->read_ready)
+      || (s->write_selected && s->write_ready))
     {
       select_printf ("already ready");
-      ready = 1;
-      goto out;
+      return true;
     }
 
   /* This is apparently necessary for the com0com driver.
@@ -1471,59 +1471,54 @@ peek_serial (select_record *s, bool)
 
       ResetEvent (fh->io_status.hEvent);
 
-      if (!ClearCommError (h, &fh->ev, &st))
+      if (!ClearCommError (h, &io_err, &st))
 	{
-	  debug_printf ("ClearCommError");
+	  debug_printf ("ClearCommError %E");
 	  goto err;
 	}
-      else if (st.cbInQue)
+      if (st.cbInQue)
 	return s->read_ready = true;
-      else if (WaitCommEvent (h, &fh->ev, &fh->io_status))
+      if (WaitCommEvent (h, &event, &fh->io_status))
 	return s->read_ready = true;
-      else if (GetLastError () == ERROR_IO_PENDING)
-	fh->overlapped_armed = 1;
-      else
+      if (GetLastError () != ERROR_IO_PENDING)
 	{
-	  debug_printf ("WaitCommEvent");
+	  debug_printf ("WaitCommEvent %E");
 	  goto err;
 	}
+      fh->overlapped_armed = 1;
     }
 
   switch (WaitForSingleObject (fh->io_status.hEvent, 10L))
     {
     case WAIT_OBJECT_0:
-      if (!ClearCommError (h, &fh->ev, &st))
+      if (!ClearCommError (h, &io_err, &st))
 	{
-	  debug_printf ("ClearCommError");
+	  debug_printf ("ClearCommError %E");
 	  goto err;
 	}
-      else if (!st.cbInQue)
-	Sleep (10L);
-      else
+      if (st.cbInQue)
 	{
-	  return s->read_ready = true;
 	  select_printf ("got something");
+	  return s->read_ready = true;
 	}
       break;
     case WAIT_TIMEOUT:
       break;
     default:
-      debug_printf ("WaitForMultipleObjects");
+      debug_printf ("WaitForMultipleObjects %E");
       goto err;
     }
 
-out:
-  return ready;
+  return 0;
 
 err:
   if (GetLastError () == ERROR_OPERATION_ABORTED)
     {
       select_printf ("operation aborted");
-      return ready;
+      return 0;
     }
 
   s->set_select_errno ();
-  select_printf ("error %E");
   return -1;
 }