From a1f0585454ea60f9e10be1f0cdcc7c0c1ceb2d0e Mon Sep 17 00:00:00 2001 From: Corinna Vinschen Date: Mon, 23 Mar 2020 17:23:19 +0100 Subject: [PATCH] Cygwin: serial: select: call ClearCommError prior to calling WaitCommEvent This (hopefully) eliminates a race condition Signed-off-by: Corinna Vinschen --- winsup/cygwin/select.cc | 26 ++++++++++++++++++-------- 1 file changed, 18 insertions(+), 8 deletions(-) diff --git a/winsup/cygwin/select.cc b/winsup/cygwin/select.cc index 07e0d82fb..b933a8ca9 100644 --- a/winsup/cygwin/select.cc +++ b/winsup/cygwin/select.cc @@ -1502,6 +1502,9 @@ verify_serial (select_record *me, fd_set *rfds, fd_set *wfds, fd_set *efds) select_record * fhandler_serial::select_read (select_stuff *ss) { + COMSTAT st; + DWORD io_err; + select_record *s = ss->start.next; s->startup = no_startup; @@ -1512,18 +1515,25 @@ fhandler_serial::select_read (select_stuff *ss) s->read_ready = false; /* This is apparently necessary for the com0com driver. See: http://cygwin.com/ml/cygwin/2009-01/msg00667.html */ + ResetEvent (io_status.hEvent); SetCommMask (get_handle_cyg (), 0); SetCommMask (get_handle_cyg (), EV_RXCHAR); - ResetEvent (io_status.hEvent); - if (!WaitCommEvent (get_handle_cyg (), &event, &io_status)) + if (ClearCommError (get_handle_cyg (), &io_err, &st) && st.cbInQue) { - if (GetLastError () == ERROR_IO_PENDING) - s->h = io_status.hEvent; - else - select_printf ("WaitCommEvent %E"); + s->read_ready = true; + return s; } - else - s->read_ready = true; + if (WaitCommEvent (get_handle_cyg (), &event, &io_status)) + { + s->read_ready = true; + return s; + } + if (GetLastError () == ERROR_IO_PENDING) + { + s->h = io_status.hEvent; + return s; + } + select_printf ("WaitCommEvent %E"); return s; }