From ddef1bbaf8ed7b106e1be10d12f1a4b6cebb77ca Mon Sep 17 00:00:00 2001
From: Timo Heister <timo.heister@gmail.com>
Date: Mon, 9 Apr 2018 16:24:19 -0400
Subject: [PATCH] make sure creating a task will initialize the thread_limit

---
 include/deal.II/base/multithread_info.h  |  5 +++++
 include/deal.II/base/thread_management.h |  2 ++
 source/base/multithread_info.cc          | 15 ++++++++++++++-
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/include/deal.II/base/multithread_info.h b/include/deal.II/base/multithread_info.h
index 97a9b6bb68..3f07766096 100644
--- a/include/deal.II/base/multithread_info.h
+++ b/include/deal.II/base/multithread_info.h
@@ -101,6 +101,11 @@ public:
    */
   static bool is_running_single_threaded ();
 
+  /**
+   * Make sure the multithreading API is initialized. This normally does not need to be called in usercode.
+   */
+  static void initialize_multithreading ();
+
 private:
 
   /**
diff --git a/include/deal.II/base/thread_management.h b/include/deal.II/base/thread_management.h
index b2f534225b..c507019309 100644
--- a/include/deal.II/base/thread_management.h
+++ b/include/deal.II/base/thread_management.h
@@ -20,6 +20,7 @@
 #include <deal.II/base/config.h>
 #include <deal.II/base/exceptions.h>
 #include <deal.II/base/template_constraints.h>
+#include <deal.II/base/multithread_info.h>
 
 #ifdef DEAL_II_WITH_THREADS
 #  include <thread>
@@ -1909,6 +1910,7 @@ namespace Threads
   -> Task<decltype(function_object())>
   {
     typedef decltype(function_object()) return_type;
+    dealii::MultithreadInfo::initialize_multithreading();
     return Task<return_type>(std::function<return_type ()>(function_object));
   }
 
diff --git a/source/base/multithread_info.cc b/source/base/multithread_info.cc
index e17e171a86..229a96db96 100644
--- a/source/base/multithread_info.cc
+++ b/source/base/multithread_info.cc
@@ -198,6 +198,19 @@ MultithreadInfo::memory_consumption ()
 }
 
 
+void
+MultithreadInfo::initialize_multithreading()
+{
+  static bool done = false;
+  if (done)
+    return;
+
+  MultithreadInfo::set_thread_limit (numbers::invalid_unsigned_int);
+  done = true;
+}
+
+
+
 const unsigned int MultithreadInfo::n_cpus = MultithreadInfo::get_n_cpus();
 unsigned int MultithreadInfo::n_max_threads = numbers::invalid_unsigned_int;
 
@@ -210,7 +223,7 @@ namespace
   {
     DoOnce ()
     {
-      MultithreadInfo::set_thread_limit (numbers::invalid_unsigned_int);
+      MultithreadInfo::initialize_multithreading();
     }
   } do_once;
 }
-- 
2.39.5