Make the subscriber_triggered_to_receive_message test more reliable. (#2584)

* Make the subscriber_triggered_to_receive_message test more reliable.

In the current code, inside of the timer we create the subscription
and the publisher, publish immediately, and expect the subscription
to get it immediately.  But it may be the case that discovery
hasn't even happened between the publisher and the subscription
by the time the publish call happens.

To make this more reliable, create the subscription and publish *before*
we ever create and spin on the timer.  This at least gives 100
milliseconds for discovery to happen.  That may not be quite enough
to make this reliable on all platforms, but in my local testing this
helps a lot.  Prior to this change I can make this fail one out of 10
times, and after the change I've run 100 times with no failures.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

Author: clalancette

rclcpp/test/rclcpp/test_add_callback_groups_to_executor.cpp

@@ -215,7 +215,6 @@ TYPED_TEST(TestAddCallbackGroupsToExecutor, add_callback_groups_after_add_node_t
   std::atomic_size_t timer_count {0};
   auto timer_callback = [&executor, &timer_count]() {
       auto cur_timer_count = timer_count++;
-      printf("in timer_callback(%zu)\n", cur_timer_count);
       if (cur_timer_count > 0) {
         executor.cancel();
       }
@@ -344,32 +343,30 @@ TYPED_TEST(TestAddCallbackGroupsToExecutorStable, subscriber_triggered_to_receiv
       received_message_promise.set_value(true);
     };
 
-  rclcpp::Subscription<test_msgs::msg::Empty>::SharedPtr subscription;
-  rclcpp::Publisher<test_msgs::msg::Empty>::SharedPtr publisher;
-  // to create a timer with a callback run on another executor
-  rclcpp::TimerBase::SharedPtr timer = nullptr;
   std::promise<void> timer_promise;
+  // create a subscription using the 'cb_grp' callback group
+  rclcpp::QoS qos = rclcpp::QoS(1).reliable();
+  auto options = rclcpp::SubscriptionOptions();
+  options.callback_group = cb_grp;
+  rclcpp::Subscription<test_msgs::msg::Empty>::SharedPtr subscription =
+    node->create_subscription<test_msgs::msg::Empty>("topic_name", qos, sub_callback, options);
+  // create a publisher to send data
+  rclcpp::Publisher<test_msgs::msg::Empty>::SharedPtr publisher =
+    node->create_publisher<test_msgs::msg::Empty>("topic_name", qos);
   auto timer_callback =
-    [&subscription, &publisher, &timer, &cb_grp, &node, &sub_callback, &timer_promise]() {
-      if (timer) {
-        timer.reset();
+    [&publisher, &timer_promise]() {
+      if (publisher->get_subscription_count() == 0) {
+        // If discovery hasn't happened yet, get out.
+        return;
       }
-
-      // create a subscription using the `cb_grp` callback group
-      rclcpp::QoS qos = rclcpp::QoS(1).reliable();
-      auto options = rclcpp::SubscriptionOptions();
-      options.callback_group = cb_grp;
-      subscription =
-        node->create_subscription<test_msgs::msg::Empty>("topic_name", qos, sub_callback, options);
-      // create a publisher to send data
-      publisher =
-        node->create_publisher<test_msgs::msg::Empty>("topic_name", qos);
       publisher->publish(test_msgs::msg::Empty());
       timer_promise.set_value();
     };
 
+  // Another executor to run the timer with a callback
   ExecutorType timer_executor;
-  timer = node->create_wall_timer(100ms, timer_callback);
+
+  rclcpp::TimerBase::SharedPtr timer = node->create_wall_timer(100ms, timer_callback);
   timer_executor.add_node(node);
   auto future = timer_promise.get_future();
   timer_executor.spin_until_future_complete(future);