[PATCH 27/34] Windows gdb: Change serial_event management

[Pedro Alves <pedro@palves.net>]

windows_nat_target::windows_continue, when it finds a resumed thread
that has a pending event, does:

	  /* There's no need to really continue, because there's already
	     another event pending.  However, we do need to inform the
	     event loop of this.  */
	  serial_event_set (m_wait_event);
	  return TRUE;

If we have more than one pending event ready to be consumed, and,
windows_nat_target::wait returns without calling
windows_nat_target::windows_continue, which it will with the non-stop
support in the following patch, then we will miss waking up the event
loop.

This patch makes windows-nat.c manage the serial_event similarly to
how linux-nat.c does it.  Clear it on entry to
windows_nat_target::wait, and set it if there may be more events to
process.  With this, there's no need to set it from
windows_nat_target::wait_for_debug_event_main_thread, so the patch
also makes us not do it.

Change-Id: I44e1682721aa4866f1dbb052b3cfb4870fb13579
---
 gdb/windows-nat.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 7a5b57b24e1..42d98badc4c 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -532,7 +532,6 @@ windows_nat_target::wait_for_debug_event_main_thread (DEBUG_EVENT *event)
 	{
 	  *event = m_last_debug_event;
 	  m_debug_event_pending = false;
-	  serial_event_clear (m_wait_event);
 	}
       else
 	wait_for_debug_event (event, INFINITE);
@@ -1838,6 +1837,11 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 {
   int pid = -1;
 
+  /* serial_event is a manual-reset event.  Clear it first.  We'll set
+     it again if we may need to wake up the event loop to get here
+     again.  */
+  serial_event_clear (m_wait_event);
+
   /* We loop when we get a non-standard exception rather than return
      with a SPURIOUS because resume can try and step or modify things,
      which needs a current_thread->h.  But some of these exceptions mark
@@ -1886,6 +1890,10 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
 		thr->suspend ();
 	    }
 
+	  /* If something came out, assume there may be more.  This is
+	     needed because there may be pending events ready to
+	     consume.  */
+	  serial_event_set (m_wait_event);
 	  return result;
 	}
       else
-- 
2.43.2