3 files changed, 22 insertions, 8 deletions

diff --git a/source/blender/render/extern/include/RE_engine.h b/source/blender/render/extern/include/RE_engine.h
index 1331c287d7c..d2ffc3a0e26 100644
--- a/source/blender/render/extern/include/RE_engine.h
+++ b/source/blender/render/extern/include/RE_engine.h
@@ -60,6 +60,7 @@ struct Scene;
 #define RE_ENGINE_PREVIEW		2
 #define RE_ENGINE_DO_DRAW		4
 #define RE_ENGINE_DO_UPDATE		8
+#define RE_ENGINE_RENDERING		16
 
 extern ListBase R_engines;
 
diff --git a/source/blender/render/intern/source/external_engine.c b/source/blender/render/intern/source/external_engine.c
index 8bdb805ada2..9053bc84bbc 100644
--- a/source/blender/render/intern/source/external_engine.c
+++ b/source/blender/render/intern/source/external_engine.c
@@ -316,6 +316,7 @@ int RE_engine_render(Render *re, int do_all)
 {
 	RenderEngineType *type = RE_engines_find(re->r.engine);
 	RenderEngine *engine;
+	int persistent_data = re->r.mode & R_PERSISTENT_DATA;
 
 	/* verify if we can render */
 	if (!type->render)
@@ -349,11 +350,17 @@ int RE_engine_render(Render *re, int do_all)
 	re->i.totface = re->i.totvert = re->i.totstrand = re->i.totlamp = re->i.tothalo = 0;
 
 	/* render */
-	if (!re->engine)
-		re->engine = RE_engine_create(type);
-
 	engine = re->engine;
 
+	if (!engine) {
+		engine = RE_engine_create(type);
+
+		if (persistent_data)
+			re->engine = engine;
+	}
+
+	engine->flag |= RE_ENGINE_RENDERING;
+
 	/* TODO: actually link to a parent which shouldn't happen */
 	engine->re = re;
 
@@ -382,8 +389,13 @@ int RE_engine_render(Render *re, int do_all)
 	if (type->render)
 		type->render(engine, re->scene);
 
-	if (!(re->r.mode & R_PERSISTENT_DATA)) {
-		RE_engine_free(re->engine);
+	engine->tile_x = 0;
+	engine->tile_y = 0;
+	engine->flag &= ~RE_ENGINE_RENDERING;
+
+	/* re->engine becomes zero if user changed active render engine during render */
+	if (!persistent_data || !re->engine) {
+		RE_engine_free(engine);
 		re->engine = NULL;
 	}
 
@@ -393,8 +405,6 @@ int RE_engine_render(Render *re, int do_all)
 		BLI_rw_mutex_unlock(&re->resultmutex);
 	}
 
-	engine->tile_x = 0;
-	engine->tile_y = 0;
 	freeparts(re);
 
 	render_result_free_list(&engine->fullresult, engine->fullresult.first);
diff --git a/source/blender/render/intern/source/pipeline.c b/source/blender/render/intern/source/pipeline.c
index 85cafa07759..f2549f04659 100644
--- a/source/blender/render/intern/source/pipeline.c
+++ b/source/blender/render/intern/source/pipeline.c
@@ -432,7 +432,10 @@ void RE_FreePersistentData(void)
 	/* render engines can be kept around for quick re-render, this clears all */
 	for (re = RenderGlobal.renderlist.first; re; re = re->next) {
 		if (re->engine) {
-			RE_engine_free(re->engine);
+			/* if engine is currently rendering, just tag it to be freed when render is finished */
+			if (!(re->engine->flag & RE_ENGINE_RENDERING))
+				RE_engine_free(re->engine);
+
 			re->engine = NULL;
 		}
 	}