Check stop condition under lock. Use emplace instead of push.

ThreadPool.h

@@ -60,10 +60,6 @@ auto ThreadPool::enqueue(F&& f, Args&&... args)
     -> std::future<typename std::result_of<F(Args...)>::type>
 {
     typedef typename std::result_of<F(Args...)>::type return_type;
-    
-    // don't allow enqueueing after stopping the pool
-    if(stop)
-        throw std::runtime_error("enqueue on stopped ThreadPool");
 
     auto task = std::make_shared< std::packaged_task<return_type()> >(
             std::bind(std::forward<F>(f), std::forward<Args>(args)...)
@@ -72,7 +68,12 @@ auto ThreadPool::enqueue(F&& f, Args&&... args)
     std::future<return_type> res = task->get_future();
     {
         std::unique_lock<std::mutex> lock(queue_mutex);
-        tasks.push([task](){ (*task)(); });
+
+        // don't allow enqueueing after stopping the pool
+        if(stop)
+            throw std::runtime_error("enqueue on stopped ThreadPool");
+
+        tasks.emplace([task](){ (*task)(); });
     }
     condition.notify_one();
     return res;