From 42780874e9e326a221c9477a20611187346c364a Mon Sep 17 00:00:00 2001
From: Daniel Garcia-Sanchez <daniel.garcia-sanchez@insp.upmc.fr>
Date: Fri, 10 Apr 2020 12:29:30 +0200
Subject: [PATCH] Use #ifdef to guard std::async

---
 examples/step-69/step-69.cc | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/examples/step-69/step-69.cc b/examples/step-69/step-69.cc
index caa9eba2b8..8e9e27ec7a 100644
--- a/examples/step-69/step-69.cc
+++ b/examples/step-69/step-69.cc
@@ -2509,7 +2509,11 @@ namespace Step69
                   output_granularity,
                   "time interval for output");
 
+#ifdef DEAL_II_WITH_THREADS
     asynchronous_writeback = true;
+#else
+    asynchronous_writeback = false;
+#endif
     add_parameter("asynchronous writeback",
                   asynchronous_writeback,
                   "Write out solution in a background thread performing IO");
@@ -2865,7 +2869,15 @@ namespace Step69
     // run in the background.
     if (!asynchronous_writeback)
       {
+#ifdef DEAL_II_WITH_THREADS
         background_thread_state = std::async(std::launch::async, output_worker);
+#else
+        AssertThrow(
+          false,
+          ExcMessage(
+            "\"asynchronous_writeback\" was set to true but deal.II was built "
+            "without thread support (\"DEAL_II_WITH_THREADS=false\")."));
+#endif
       }
     else
       {
-- 
2.39.5