From e76fd99c472237125f03d46ed7bff915e2d6a20b Mon Sep 17 00:00:00 2001
From: glx <glx@openttd.org>
Date: Fri, 25 Jan 2019 21:22:49 +0100
Subject: [PATCH] Fix #7007: deadlock when launched with -n switch

---
 src/gfx.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/gfx.cpp b/src/gfx.cpp
index 605ff7664b..85cd3bfb59 100644
--- a/src/gfx.cpp
+++ b/src/gfx.cpp
@@ -1317,7 +1317,11 @@ void DrawDirtyBlocks()
 		/* Wait a while and update _realtime_tick so we are given the rights */
 		if (!IsFirstModalProgressLoop()) CSleep(MODAL_PROGRESS_REDRAW_TIMEOUT);
 		_realtime_tick += MODAL_PROGRESS_REDRAW_TIMEOUT;
+
+		/* Modal progress thread may need blitter access while we are waiting for it. */
+		VideoDriver::GetInstance()->ReleaseBlitterLock();
 		_modal_progress_paint_mutex->BeginCritical();
+		VideoDriver::GetInstance()->AcquireBlitterLock();
 		_modal_progress_work_mutex->BeginCritical();
 
 		/* When we ended with the modal progress, do not draw the blocks.