hw/xwin: Fix clipboard thread restart

It seems that the clipboard thread restart mechanism has been broken for a
while, which can be demonstrated using XDMCP with KDM (e.g. to a Kubutunu 12.04
host)

KDM kills all attached clients, including the clipboard integration client,
which restarts, but then exits on WM_QUIT.

Using PostQuitMessage() in WM_DESTROY is unhelpful, as we may not actually be
quitting the thread, if we just destroyed the window because the clipboard
thread is about to retry, because he WM_QUIT message sticks around, and is
noticed the next time we look at the window message queue and confuses us into
thinking we need to quit.

Sending a WM_DESTROY is apparently never correct anyhow, see [1]

So:

1/ Use DestroyWindow() to destroy the clipboard messaging window when cleaning
up for retry or exit in winClipboardProc (the clipboard thread main proc)

2/ Send a special WM_WM_QUIT message in winClipboardWindowDestroy() from the X
server thread when the X server is resetting.

3/ When processing that WM_WM_QUIT message in the clipboard thread, cause the
clipboard window to PostQuitMessage(), which causes the clipboard thread to
exit.

[1] http://blogs.msdn.com/b/oldnewthing/archive/2011/09/26/10216420.aspx

Signed-off-by: Jon TURNEY <jon.turney@dronecode.org.uk>
Reviewed-by: Colin Harrison <colin.harrison@virgin.net>

3 files changed, 9 insertions, 2 deletions

diff --git a/hw/xwin/winclipboard/internal.h b/hw/xwin/winclipboard/internal.h
index bcf45ca4d..c6bde84af 100644
--- a/hw/xwin/winclipboard/internal.h
+++ b/hw/xwin/winclipboard/internal.h
@@ -44,6 +44,7 @@
 #define WIN_XEVENTS_NOTIFY_TARGETS		4
 
 #define WM_WM_REINIT                           (WM_USER + 1)
+#define WM_WM_QUIT                             (WM_USER + 2)
 
 /*
  * References to external symbols
diff --git a/hw/xwin/winclipboard/thread.c b/hw/xwin/winclipboard/thread.c
index 786b88972..50e1e8cb5 100644
--- a/hw/xwin/winclipboard/thread.c
+++ b/hw/xwin/winclipboard/thread.c
@@ -351,7 +351,7 @@ winClipboardProc(Bool fUseUnicode, char *szDisplay)
  winClipboardProc_Done:
     /* Close our Windows window */
     if (g_hwndClipboard) {
-        winClipboardWindowDestroy();
+        DestroyWindow(g_hwndClipboard);
     }
 
     /* Close our X window */
@@ -491,7 +491,7 @@ void
 winClipboardWindowDestroy(void)
 {
   if (g_hwndClipboard) {
-    SendMessage(g_hwndClipboard, WM_DESTROY, 0, 0);
+    SendMessage(g_hwndClipboard, WM_WM_QUIT, 0, 0);
   }
 }
 
diff --git a/hw/xwin/winclipboard/wndproc.c b/hw/xwin/winclipboard/wndproc.c
index b63a1dc5c..a17f8a900 100644
--- a/hw/xwin/winclipboard/wndproc.c
+++ b/hw/xwin/winclipboard/wndproc.c
@@ -154,6 +154,12 @@ winClipboardWindowProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
         ChangeClipboardChain(hwnd, s_hwndNextViewer);
 
         s_hwndNextViewer = NULL;
+    }
+        return 0;
+
+    case WM_WM_QUIT:
+    {
+        winDebug("winClipboardWindowProc - WM_WM_QUIT\n");
 
         PostQuitMessage(0);
     }