(svn r27775) -Fix [FS#6510]: Insufficient thread synchronisation when switching blitters. (JGR)

src/video/video_driver.hpp

@@ -49,6 +49,7 @@ public:
 
 	/**
 	 * Callback invoked after the blitter was changed.
+	 * This may only be called between AcquireBlitterLock and ReleaseBlitterLock.
 	 * @return True if no error.
 	 */
 	virtual bool AfterBlitterChange()
@@ -56,6 +57,18 @@ public:
 		return true;
 	}
 
+	/**
+	 * Acquire any lock(s) required to be held when changing blitters.
+	 * These lock(s) may not be acquired recursively.
+	 */
+	virtual void AcquireBlitterLock() { }
+
+	/**
+	 * Release any lock(s) required to be held when changing blitters.
+	 * These lock(s) may not be acquired recursively.
+	 */
+	virtual void ReleaseBlitterLock() { }
+
 	virtual bool ClaimMousePointer()
 	{
 		return true;