[PATCH v2 1/4] winex11.drv: Call XFlush() right after XUngrabServer().

[Zhiyi Zhang]

XGrabServer() stops the processing of other display connections
until a XUngrabServer() call is actually processed by the X server.

Now consider the following scenario:
Thread 1: XGrabServer -> ... -> XUngrabServer -> Grab mutex A
Thread 2: Grab mutex A -> Do something with another display connection

Before the XUngrabServer() request is actually processed by the X server,
go on grabbing mutex A could trigger a lock because processing another
display connection in thread 2 is blocked by thread 1 calling XGrabServer
and thread 1 is blocked by thread 2 grabbing the same mutex.
With thread 1 freezed, the XUngrabServer may never reach the X server,
thus a deadlock.

By adding a XFlush() call right after XUngrabServer(), we avoid such a
race condition.

Signed-off-by: Zhiyi Zhang <zzhang at codeweavers.com>
---
v2: Fix a possible deadlock as described above. Supersede 171243~171245

 dlls/winex11.drv/palette.c | 1 +
 dlls/winex11.drv/xrandr.c  | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/dlls/winex11.drv/palette.c b/dlls/winex11.drv/palette.c
index bba2253264..073761a5ee 100644
--- a/dlls/winex11.drv/palette.c
+++ b/dlls/winex11.drv/palette.c
@@ -480,6 +480,7 @@ static BOOL X11DRV_PALETTE_BuildSharedMap( const PALETTEENTRY *sys_pal_template
         palette_size = c_min + NB_RESERVED_COLORS;
 
 	XUngrabServer(gdi_display);
+	XFlush(gdi_display);
 
 	TRACE("adjusted size %i colorcells\n", palette_size);
      }
diff --git a/dlls/winex11.drv/xrandr.c b/dlls/winex11.drv/xrandr.c
index 6bb2b18ce7..85da5efea3 100644
--- a/dlls/winex11.drv/xrandr.c
+++ b/dlls/winex11.drv/xrandr.c
@@ -419,6 +419,7 @@ static LONG xrandr12_set_current_mode( int mode )
     if (status != RRSetConfigSuccess)
     {
         XUngrabServer( gdi_display );
+        XFlush( gdi_display );
         ERR("Failed to disable CRTC.\n");
         pXRRFreeCrtcInfo( crtc_info );
         pXRRFreeScreenResources( resources );
@@ -440,6 +441,7 @@ static LONG xrandr12_set_current_mode( int mode )
                                 crtc_info->rotation, crtc_info->outputs, crtc_info->noutput );
 
     XUngrabServer( gdi_display );
+    XFlush( gdi_display );
 
     pXRRFreeCrtcInfo( crtc_info );
     pXRRFreeScreenResources( resources );
-- 
2.23.0