Instrument rejected tasks in ThreadPoolExecutor

metrics-core/src/main/java/io/dropwizard/metrics5/InstrumentedExecutorService.java

@@ -9,6 +9,7 @@
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.ForkJoinPool;
 import java.util.concurrent.Future;
+import java.util.concurrent.RejectedExecutionHandler;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -30,6 +31,7 @@ public class InstrumentedExecutorService implements ExecutorService {
     private final Meter submitted;
     private final Counter running;
     private final Meter completed;
+    private final Counter rejected;
     private final Timer idle;
     private final Timer duration;
 
@@ -57,6 +59,7 @@ public InstrumentedExecutorService(ExecutorService delegate, MetricRegistry regi
         this.submitted = registry.meter(MetricRegistry.name(name, "submitted"));
         this.running = registry.counter(MetricRegistry.name(name, "running"));
         this.completed = registry.meter(MetricRegistry.name(name, "completed"));
+        this.rejected = registry.counter(MetricRegistry.name(name, "rejected"));
         this.idle = registry.timer(MetricRegistry.name(name, "idle"));
         this.duration = registry.timer(MetricRegistry.name(name, "duration"));
 
@@ -81,6 +84,8 @@ private void registerInternalMetrics() {
                     queue::size);
             registry.registerGauge(MetricRegistry.name(name, "tasks.capacity"),
                     queue::remainingCapacity);
+            RejectedExecutionHandler delegateHandler = executor.getRejectedExecutionHandler();
+            executor.setRejectedExecutionHandler(new InstrumentedRejectedExecutionHandler(delegateHandler));
         } else if (delegate instanceof ForkJoinPool) {
             ForkJoinPool forkJoinPool = (ForkJoinPool) delegate;
             registry.registerGauge(MetricRegistry.name(name, "tasks.stolen"),
@@ -223,6 +228,20 @@ public boolean awaitTermination(long l, TimeUnit timeUnit) throws InterruptedExc
         return delegate.awaitTermination(l, timeUnit);
     }
 
+    private class InstrumentedRejectedExecutionHandler implements RejectedExecutionHandler {
+        private final RejectedExecutionHandler delegateHandler;
+
+        public InstrumentedRejectedExecutionHandler(RejectedExecutionHandler delegateHandler) {
+            this.delegateHandler = delegateHandler;
+        }
+
+        @Override
+        public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
+            rejected.inc();
+            this.delegateHandler.rejectedExecution(r, executor);
+        }
+    }
+
     private class InstrumentedRunnable implements Runnable {
         private final Runnable task;
         private final Timer.Context idleContext;

metrics-core/src/test/java/io/dropwizard/metrics5/InstrumentedExecutorServiceTest.java

@@ -8,14 +8,17 @@
 
 import java.time.Duration;
 import java.util.concurrent.Callable;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.ThreadPoolExecutor;
 import java.util.concurrent.TimeUnit;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 class InstrumentedExecutorServiceTest {
 
@@ -166,6 +169,32 @@ void reportsTasksInformationForThreadPoolExecutor() throws Exception {
         assertThat(poolSize.getValue()).isEqualTo(1);
     }
 
+    @Test
+    public void reportsRejectedTasksForThreadPoolExecutor() throws Exception {
+        executor = new ThreadPoolExecutor(1, 1,
+                0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<>(1));
+        instrumentedExecutorService = new InstrumentedExecutorService(executor, registry, "tp");
+        final Counter rejected = registry.counter("tp.rejected");
+        assertThat(rejected.getCount()).isEqualTo(0);
+
+        final CountDownLatch latch = new CountDownLatch(1);
+
+        Runnable runnable = () -> {
+            try {
+                latch.await();
+            } catch (InterruptedException e) {
+                throw new RuntimeException(e);
+            }
+        };
+
+        Future<?> executingFuture = instrumentedExecutorService.submit(runnable);
+        Future<?> queuedFuture = instrumentedExecutorService.submit(runnable);
+        assertThatThrownBy(() -> instrumentedExecutorService.submit(runnable))
+                .isInstanceOf(RejectedExecutionException.class);
+        latch.countDown();
+        assertThat(rejected.getCount()).isEqualTo(1);
+    }
+
     @Test
     public void removesMetricsAfterShutdownForThreadPoolExecutor() {
         executor = new ThreadPoolExecutor(4, 16,

metrics-legacy-adapter/src/test/java/com/codahale/metrics/InstrumentedExecutorServiceTest.java

@@ -29,6 +29,6 @@ void testCreate() throws Exception {
 
         assertThat(registry.getMetrics()).containsOnlyKeys("test-instrumented.completed",
                 "test-instrumented.submitted", "test-instrumented.duration", "test-instrumented.idle",
-                "test-instrumented.running");
+                "test-instrumented.running", "test-instrumented.rejected");
     }
 }