Add DequeuePlusAction

src/threaded_queue.h

@@ -94,7 +94,9 @@ public:
   }
 
   // Get the first element from the queue. Blocks until one is available.
-  T Dequeue() {
+  // Executes |action| with an acquired |mutex_|.
+  template<typename TAction>
+  T DequeuePlusAction(TAction& action) {
     std::unique_lock<std::mutex> lock(mutex_);
     waiter_->cv.wait(lock, [&]() {
       return !priority_.empty() || !queue_.empty();
@@ -108,9 +110,17 @@ public:
 
     auto val = std::move(queue_.front());
     queue_.pop();
+
+    action();
+
     return std::move(val);
   }
 
+  // Get the first element from the queue. Blocks until one is available.
+  T Dequeue() {
+    return DequeuePlusAction([]() {});
+  }
+
   // Get the first element from the queue without blocking. Returns a null
   // value if the queue is empty.
   optional<T> TryDequeue() {