Fix a race condition where we might get updates thrown at us right after a
framebuffer switch, but before we've been given the pointer to the new
framebuffer.


git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4839 3789f03b-4d11-0410-bbf8-ca57d06f2519
diff --git a/common/rfb/VNCServer.h b/common/rfb/VNCServer.h
index 4e55479..280b68b 100644
--- a/common/rfb/VNCServer.h
+++ b/common/rfb/VNCServer.h
@@ -30,6 +30,13 @@
 
   class VNCServer : public UpdateTracker {
   public:
+    // blockUpdates()/unblockUpdates() tells the server that the pixel buffer
+    // is currently in flux and may not be accessed. The attributes of the
+    // pixel buffer may still be accessed, but not the frame buffer itself.
+    // Note that access must be unblocked the exact same number of times it
+    // was blocked.
+    virtual void blockUpdates() = 0;
+    virtual void unblockUpdates() = 0;
 
     // setPixelBuffer() tells the server to use the given pixel buffer (and
     // optionally a modified screen layout).  If this differs in size from