detach threads later

inst/include/utils.h

@@ -111,7 +111,10 @@ class ThreadPool {
   ~ThreadPool() {
     event_loop.stop();
     for(auto& thread : threads) {
-      thread.join();
+      // Ideally we would join those threads, but this deadlocks on Windows.
+      // Detaching seems fine as after `stop` we're making sure that all tasks
+      // are done.
+      thread.detach();
     }
   }
 };