add feed refresh engine metrics

commafeed-client/src/pages/admin/MetricsPage.tsx

@@ -1,6 +1,7 @@
-import { Accordion, Tabs } from "@mantine/core"
+import { Accordion, Box, Tabs } from "@mantine/core"
 import { client } from "app/client"
 import { Loader } from "components/Loader"
+import { Gauge } from "components/metrics/Gauge"
 import { Meter } from "components/metrics/Meter"
 import { MetricAccordionItem } from "components/metrics/MetricAccordionItem"
 import { Timer } from "components/metrics/Timer"
@@ -15,11 +16,17 @@ const shownMeters: { [key: string]: string } = {
     "com.commafeed.backend.feed.FeedRefreshUpdater.entryCacheMiss": "Entry cache miss rate",
 }
 
+const shownGauges: { [key: string]: string } = {
+    "com.commafeed.backend.feed.FeedRefreshEngine.queue.size": "Queue size",
+    "com.commafeed.backend.feed.FeedRefreshEngine.worker.active": "Feed Worker active",
+    "com.commafeed.backend.feed.FeedRefreshEngine.updater.active": "Feed Updater active",
+}
+
 export function MetricsPage() {
     const query = useAsync(() => client.admin.getMetrics(), [])
 
     if (!query.result) return <Loader />
-    const { meters, timers } = query.result.data
+    const { meters, gauges, timers } = query.result.data
     return (
         <Tabs defaultValue="stats">
             <Tabs.List>
@@ -39,6 +46,15 @@ export function MetricsPage() {
                         </MetricAccordionItem>
                     ))}
                 </Accordion>
+
+                <Box pt="xs">
+                    {Object.keys(shownGauges).map(g => (
+                        <Box key={g}>
+                            <span>{shownGauges[g]}&nbsp;</span>
+                            <Gauge gauge={gauges[g]} />
+                        </Box>
+                    ))}
+                </Box>
             </Tabs.Panel>
 
             <Tabs.Panel value="timers" pt="xs">

commafeed-server/src/main/java/com/commafeed/backend/feed/FeedRefreshEngine.java

@@ -18,6 +18,7 @@ import javax.inject.Singleton;
 import org.apache.commons.lang3.time.DateUtils;
 import org.hibernate.SessionFactory;
 
+import com.codahale.metrics.Gauge;
 import com.codahale.metrics.Meter;
 import com.codahale.metrics.MetricRegistry;
 import com.commafeed.CommaFeedConfiguration;
@@ -45,8 +46,8 @@ public class FeedRefreshEngine implements Managed {
 	private final ExecutorService feedProcessingLoopExecutor;
 	private final ExecutorService refillLoopExecutor;
 	private final ExecutorService refillExecutor;
-	private final ExecutorService workerExecutor;
+	private final ThreadPoolExecutor workerExecutor;
-	private final ExecutorService databaseUpdaterExecutor;
+	private final ThreadPoolExecutor databaseUpdaterExecutor;
 
 	@Inject
 	public FeedRefreshEngine(SessionFactory sessionFactory, FeedDAO feedDAO, FeedRefreshWorker worker, FeedRefreshUpdater updater,
@@ -65,6 +66,10 @@ public class FeedRefreshEngine implements Managed {
 		this.refillExecutor = newDiscardingSingleThreadExecutorService();
 		this.workerExecutor = newBlockingExecutorService(config.getApplicationSettings().getBackgroundThreads());
 		this.databaseUpdaterExecutor = newBlockingExecutorService(config.getApplicationSettings().getDatabaseUpdateThreads());
+
+		metrics.register(MetricRegistry.name(getClass(), "queue", "size"), (Gauge<Integer>) queue::size);
+		metrics.register(MetricRegistry.name(getClass(), "worker", "active"), (Gauge<Integer>) workerExecutor::getActiveCount);
+		metrics.register(MetricRegistry.name(getClass(), "updater", "active"), (Gauge<Integer>) databaseUpdaterExecutor::getActiveCount);
 	}
 
 	@Override
@@ -185,7 +190,7 @@ public class FeedRefreshEngine implements Managed {
 	/**
 	 * returns an ExecutorService with a single thread that discards tasks if a task is already running
 	 */
-	private ExecutorService newDiscardingSingleThreadExecutorService() {
+	private ThreadPoolExecutor newDiscardingSingleThreadExecutorService() {
 		ThreadPoolExecutor pool = new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new SynchronousQueue<>());
 		pool.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());
 		return pool;
@@ -194,7 +199,7 @@ public class FeedRefreshEngine implements Managed {
 	/**
 	 * returns an ExecutorService that blocks submissions until a thread is available
 	 */
-	private ExecutorService newBlockingExecutorService(int threads) {
+	private ThreadPoolExecutor newBlockingExecutorService(int threads) {
 		ThreadPoolExecutor pool = new ThreadPoolExecutor(threads, threads, 0L, TimeUnit.MILLISECONDS, new SynchronousQueue<>());
 		pool.setRejectedExecutionHandler((r, e) -> {
 			if (e.isShutdown()) {