sequence: add keep-going feature

When enabling the 'keep_going' config attribute, the component will
carry on in case a child exited with an error. In addition, if the
'restart' attribute is set it will start executing the children from
the beginning.

repos/os/src/app/sequence/README

@@ -1,7 +1,7 @@
 This directory contains a simple utility to serialize the execution of
-multiple components. It is configured with "start" XML nodes much like
+multiple components. It is configured with '<start>' XML nodes much like
-_init_ however this component relies on its parent to manage all routing
+_init_. However, this component relies on its parent to manage all routing
-and resources, with the exception of a "config" ROM. No services are
+and resources, with the exception of a 'config' ROM. No services are
 propagated from children to the parent.
 
 A sample configuration to start a consumer after a producer has exited:
@@ -24,3 +24,17 @@ A sample configuration to start a consumer after a producer has exited:
 !     </start>
 !   </config>
 ! </start>
+
+There are a few optional '<config>' attributes that control the way the
+component operates:
+
+* 'repeat' will instruct the component to repeat the sequence again
+  starting from the first '<start>' node when it has reached the end.
+  The default is 'false'.
+
+* 'keep_going' will instruct the component to start the next child
+  in case the previous one exited with an error. The default is 'false'.
+
+* 'restart' instructs the component to start from the top of the
+  sequence. It is only evaluted when 'keep_going' is enabled. The
+  default is 'false'.

repos/os/src/app/sequence/main.cc

@@ -75,6 +75,8 @@ struct Sequence::Child : Genode::Child_policy
 
 	Genode::Child _child { _env.rm(), _env.ep().rpc_ep(), *this };
 
+	int _exit_value = -1;
+
 	Child(Genode::Env &env,
 	      Xml_node const &start_node,
 	      Signal_context_capability exit_handler)
@@ -96,6 +98,8 @@ struct Sequence::Child : Genode::Child_policy
 			destroy(_services_heap, &service); });
 	}
 
+	int exit_value() const { return _exit_value; }
+
 
 	/****************************
 	 ** Child_policy interface **
@@ -138,18 +142,14 @@ struct Sequence::Child : Genode::Child_policy
 	Pd_session_capability ref_pd_cap() const override { return _env.pd_session_cap(); }
 
 	/**
-	 * If the exit is successful then queue a child reload via a signal,
+	 * Always queue a reload signal and store the exit value. The
-	 * otherwise exit this parent component.
+	 * parent will then determine which action to take by looking
+	 * at the exit value.
 	 */
 	void exit(int exit_value) override
 	{
-		if (exit_value == 0)
+		_exit_value = exit_value;
-			_exit_transmitter.submit();
+		_exit_transmitter.submit();
-		else {
-			error("child \"", name(), "\" exited with exit value ", exit_value);
-			_env.parent().exit(exit_value);
-			sleep_forever();
-		}
 	}
 
 	/**
@@ -230,7 +230,31 @@ struct Sequence::Main
 
 void Sequence::Main::start_next_child()
 {
-	if (child.constructed())
+	bool const constructed = child.constructed();
+
+	/*
+	 * In case the child exited with an error check if we
+	 * still should keep-going and when doing so if the
+	 * sequence should be restarted.
+	 */
+	if (constructed && child->exit_value()) {
+		bool const keep_going = config_xml.attribute_value("keep_going", false);
+		bool const restart    = config_xml.attribute_value("restart", false);
+
+		warning("child \"", child->name(), "\" exited with exit value ",
+		        child->exit_value());
+
+		if (!keep_going) {
+			env.parent().exit(child->exit_value());
+			sleep_forever();
+		}
+
+		warning("keep-going", restart ? " starting from the beginning" : "");
+		if (restart)
+			next_xml_index = 0;
+	}
+
+	if (constructed)
 		child.destruct();
 
 	try { while (true) {