add example for guard conditions

rcldotnet_examples/CMakeLists.txt

@@ -45,9 +45,16 @@ add_dotnet_executable(rcldotnet_example_client
   ${_assemblies_dep_dlls}
 )
 
+add_dotnet_executable(rcldotnet_guard_condition
+  RCLDotnetGuardCondition.cs
+  INCLUDE_DLLS
+  ${_assemblies_dep_dlls}
+)
+
 install_dotnet(rcldotnet_talker DESTINATION lib/${PROJECT_NAME}/dotnet)
 install_dotnet(rcldotnet_listener DESTINATION lib/${PROJECT_NAME}/dotnet)
 install_dotnet(rcldotnet_example_service DESTINATION lib/${PROJECT_NAME}/dotnet)
 install_dotnet(rcldotnet_example_client DESTINATION lib/${PROJECT_NAME}/dotnet)
+install_dotnet(rcldotnet_guard_condition DESTINATION lib/${PROJECT_NAME}/dotnet)
 
 ament_package()

rcldotnet_examples/RCLDotnetGuardCondition.cs

@@ -0,0 +1,50 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+using ROS2;
+
+namespace ConsoleApplication
+{
+    public static class RCLDotnetGuardCondition
+    {
+        static GuardCondition _guardCondition = null;
+
+        public static void Main(string[] args)
+        {
+            RCLdotnet.Init();
+
+            var node = RCLdotnet.CreateNode("guard_condition_example");
+
+            _guardCondition = node.CreateGuardCondition(GuardConditionTriggered);
+
+            Console.WriteLine($"RMWIdentifier: {RCLdotnet.GetRMWIdentifier()}");
+
+            _guardCondition.Trigger();
+            Console.WriteLine($"{DateTimeOffset.Now:O} ThreadId: {Environment.CurrentManagedThreadId} - Initial trigger of GuardCondition.");
+
+            RCLdotnet.Spin(node);
+        }
+
+        static void GuardConditionTriggered()
+        {
+            Console.WriteLine($"{DateTimeOffset.Now:O} ThreadId: {Environment.CurrentManagedThreadId} - GuardCondition was triggered.");
+            _ = TriggerAfterSomeTime();
+        }
+
+        static async Task TriggerAfterSomeTime()
+        {
+            // This is a multiple of the 500ms used in the loop in
+            // RCLdotnet.Spin(). So the guard condition will be triggered nearly
+            // at the same time as the wait times out. This is to test/reproduce
+            // if the combination of rcldotnet and the rmw implementation have
+            // an race-conditions in that case.
+            await Task.Delay(TimeSpan.FromSeconds(1));
+
+            // This will be called in an background worker thread as console
+            // applications don't have an SynchronizationContext by default.
+            _guardCondition.Trigger();
+            Console.WriteLine($"{DateTimeOffset.Now:O} ThreadId: {Environment.CurrentManagedThreadId} - Triggered GuardCondition.");
+        }
+    }
+}