Add async.task.finished metric.

Author: ioquatix

lib/metrics/provider/async/task.rb

@@ -8,10 +8,15 @@
 
 Metrics::Provider(Async::Task) do
 	ASYNC_TASK_SCHEDULED = Metrics.metric("async.task.scheduled", :counter, description: "The number of tasks scheduled.")
+	ASYNC_TASK_FINISHED = Metrics.metric("async.task.finished", :counter, description: "The number of tasks finished.")
 
 	def schedule(&block)
 		ASYNC_TASK_SCHEDULED.emit(1)
 
 		super(&block)
+	rescue => error
+		raise
+	ensure
+		ASYNC_TASK_FINISHED.emit(1)
 	end
 end