[dataflow] Add a flag to indicate that some nodes cannot be put on se…

…parate task threads

src/ossia/dataflow/graph/graph_parallel_impl.hpp

@@ -154,6 +154,20 @@ class executor
 
   void set_task_executor(task_function f) { m_func = std::move(f); }
 
+  void enqueue_task(task& task)
+  {
+    if(task.m_node->not_threadable())
+    {
+      [[unlikely]];
+      m_not_threadsafe_tasks.enqueue(&task);
+    }
+    else
+    {
+      [[likely]];
+      m_tasks.enqueue(&task);
+    }
+  }
+
   void run(taskflow& tf)
   {
     m_tf = &tf;
@@ -199,7 +213,7 @@ class executor
           assert(task.m_dependencies == 0);
 #endif
           std::atomic_thread_fence(std::memory_order_release);
-          m_tasks.enqueue(&task);
+          enqueue_task(task);
         }
 #if defined(DISABLE_DONE_TASKS)
         else
@@ -221,6 +235,11 @@ class executor
     while(m_doneTasks.load(std::memory_order_relaxed) != m_toDoTasks)
     {
       task* t{};
+      if(m_not_threadsafe_tasks.wait_dequeue_timed(t, 1))
+      {
+        execute(*t);
+      }
+
       if(m_tasks.wait_dequeue_timed(t, 1))
       {
         execute(*t);
@@ -266,7 +285,7 @@ class executor
           }
 #endif
           std::atomic_thread_fence(std::memory_order_release);
-          m_tasks.enqueue(&nextTask);
+          enqueue_task(nextTask);
         }
 #if defined(DISABLE_DONE_TASKS)
         else
@@ -336,6 +355,7 @@ class executor
   std::size_t m_toDoTasks = 0;
 
   moodycamel::BlockingConcurrentQueue<task*> m_tasks;
+  moodycamel::BlockingConcurrentQueue<task*> m_not_threadsafe_tasks;
 
 #if defined(CHECK_EXEC_COUNTS)
   std::array<std::atomic_int, 5000> m_checkVec;

src/ossia/dataflow/graph_node.hpp

@@ -154,6 +154,16 @@ class OSSIA_EXPORT graph_node
   void set_mute(bool b) noexcept { m_muted = b; }
   [[nodiscard]] bool muted() const noexcept { return m_muted; }
 
+  /**
+   * Indicates that the node implementation must always be scheduled on the same thread.
+   * Main use case: QJSEngine which is not thread-safe.
+   */
+  [[nodiscard]]
+  bool not_threadable() const noexcept
+  {
+    return m_not_threadable;
+  }
+
   virtual void all_notes_off() noexcept;
   token_request_vec requested_tokens;
 
@@ -162,6 +172,7 @@ class OSSIA_EXPORT graph_node
   outlets m_outlets;
 
   bool m_executed{};
+  bool m_not_threadable{};
 
 private:
   bool m_start_discontinuous{};