init: reduce report latency for resource requests

In contrast to most information of init's state reports, which can be
monitored at a relatively low rate (like 2 seconds in Sculpt's runtime),
resource requests call for an immediate response by the consumer of the
report. Otherwise the requesting child stays unnecessarily blocked until
the next rate-limited state report is due. This patch adds a fast lane
for such low-latency state updates to init.

repos/os/src/init/child.cc

@@ -641,7 +641,7 @@ void Init::Child::resource_request(Parent::Resource_args const &args)
 	log("child \"", name(), "\" requests resources: ", args);
 
 	_requested_resources.construct(args);
-	_report_update_trigger.trigger_report_update();
+	_report_update_trigger.trigger_immediate_report_update();
 }
 
 

repos/os/src/init/report.h

@@ -68,7 +68,20 @@ class Init::Report_detail : Genode::Noncopyable
 
 struct Init::Report_update_trigger : Interface
 {
+	/**
+	 * Trigger regular (rate-limited) report update
+	 */
 	virtual void trigger_report_update() = 0;
+
+	/**
+	 * Trigger immediate report update
+	 *
+	 * This method is intended for situations that require a timely response of
+	 * the consumer of the report. This is particularly important for resource
+	 * requests that would otherwise unnecessarily stall the execution of the
+	 * respective child.
+	 */
+	virtual void trigger_immediate_report_update() = 0;
 };
 
 #endif /* _SRC__INIT__REPORT_H_ */

repos/os/src/init/state_reporter.h

@@ -63,6 +63,9 @@ class Init::State_reporter : public Report_update_trigger
 		Signal_handler<State_reporter> _timer_periodic_handler {
 			_env.ep(), *this, &State_reporter::_handle_timer };
 
+		Signal_handler<State_reporter> _immediate_handler {
+			_env.ep(), *this, &State_reporter::_handle_timer };
+
 		bool _scheduled = false;
 
 		void _handle_timer()
@@ -183,6 +186,12 @@ class Init::State_reporter : public Report_update_trigger
 				_scheduled = true;
 			}
 		}
+
+		void trigger_immediate_report_update() override
+		{
+			if (_report_delay_ms)
+				Signal_transmitter(_immediate_handler).submit();
+		}
 };
 
 #endif /* _SRC__INIT__STATE_REPORTER_H_ */

repos/ports/src/app/gdb_monitor/app_child.h

@@ -172,9 +172,10 @@ class Gdb_monitor::App_child : public Child_policy,
 		}
 
 		/**
-		 * Init::Report_update_trigger callback
+		 * Init::Report_update_trigger callbacks
 		 */
 		void trigger_report_update() override { }
+		void trigger_immediate_report_update() override { }
 
 		/**
 		 * Init::Routed_service::Ram_accessor interface