Windows gdb: Simplify windows_nat_target::wait

The logic in windows_nat_target::wait, where we decide what to do
depending on the result from get_windows_debug_event is harder to
grasp than it looks.

It is not easy to tell what should happen when in async mode
get_windows_debug_event returns that there's no event to process.

And then, if get_windows_debug_event returns null_ptid /
TARGET_WAITKIND_SPURIOUS, then we need to issue a ContinueDebugEvent.

There's also this comment in windows_nat_target::wait, which we're not
really implementing today:

~~~~
  /* 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
     the birth or death of threads, which mean that the current thread
     isn't necessarily what you think it is.  */
~~~~

This patch changes things a bit so that the code is more obvious:

 - look at the status kind, instead of ptid_t.

 - add an explicit early return case for no-event.

 - add an explicit case for TARGET_WAITKIND_SPURIOUS.

 - with those, we no longer need to handle the case of find_thread not
   finding a thread, so we can drop one indentation level.

Change-Id: I76c41762e1f893a7ff23465856ccf6a44af1f0e7

1 files changed, 25 insertions, 16 deletions

diff --git a/gdb/windows-nat.c b/gdb/windows-nat.c
index 9b1bede..9730377 100644
--- a/gdb/windows-nat.c
+++ b/gdb/windows-nat.c
@@ -1764,7 +1764,10 @@ windows_nat_target::get_windows_debug_event
     }
 
   if (thread_id == 0)
-    return null_ptid;
+    {
+      ourstatus->set_ignore ();
+      return null_ptid;
+    }
   return ptid_t (windows_process.current_event.dwProcessId, thread_id, 0);
 }
 
@@ -1785,27 +1788,33 @@ windows_nat_target::wait (ptid_t ptid, struct target_waitstatus *ourstatus,
     {
       ptid_t result = get_windows_debug_event (pid, ourstatus, options);
 
-      if (result != null_ptid)
+      if ((options & TARGET_WNOHANG) != 0
+	  && ourstatus->kind () == TARGET_WAITKIND_IGNORE)
+	return result;
+
+      if (ourstatus->kind () == TARGET_WAITKIND_SPURIOUS)
+	{
+	  CHECK (windows_continue (DBG_CONTINUE,
+				   windows_process.desired_stop_thread_id, 0));
+	}
+      else if (ourstatus->kind () != TARGET_WAITKIND_IGNORE)
 	{
 	  if (ourstatus->kind () != TARGET_WAITKIND_EXITED
-	      && ourstatus->kind () !=  TARGET_WAITKIND_SIGNALLED)
+	      && ourstatus->kind () != TARGET_WAITKIND_SIGNALLED)
 	    {
 	      windows_thread_info *th = windows_process.find_thread (result);
 
-	      if (th != nullptr)
+	      th->stopped_at_software_breakpoint = false;
+	      if (windows_process.current_event.dwDebugEventCode
+		  == EXCEPTION_DEBUG_EVENT
+		  && ((windows_process.current_event.u.Exception.ExceptionRecord.ExceptionCode
+		       == EXCEPTION_BREAKPOINT)
+		      || (windows_process.current_event.u.Exception.ExceptionRecord.ExceptionCode
+			  == STATUS_WX86_BREAKPOINT))
+		  && windows_process.windows_initialization_done)
 		{
-		  th->stopped_at_software_breakpoint = false;
-		  if (windows_process.current_event.dwDebugEventCode
-		      == EXCEPTION_DEBUG_EVENT
-		      && ((windows_process.current_event.u.Exception.ExceptionRecord.ExceptionCode
-			   == EXCEPTION_BREAKPOINT)
-			  || (windows_process.current_event.u.Exception.ExceptionRecord.ExceptionCode
-			      == STATUS_WX86_BREAKPOINT))
-		      && windows_process.windows_initialization_done)
-		    {
-		      th->stopped_at_software_breakpoint = true;
-		      th->pc_adjusted = false;
-		    }
+		  th->stopped_at_software_breakpoint = true;
+		  th->pc_adjusted = false;
 		}
 	    }