SingleThreadEventExecutor ignores startThread failures

Motivation:

When doStartThread throws an exception, e.g. due to the actual executor being depleted of threads and throwing in its rejected execution handler, the STEE ends up in started state anyway. If we try to execute another task in this executor, it will be queued but the thread won't be started anymore and the task will linger forever.

Modifications:

- Ensure we not update the internal state if the startThread() method throws.
- Add testcase

Result:

Fixes [#7483]

common/src/main/java/io/netty/util/concurrent/SingleThreadEventExecutor.java

@@ -16,6 +16,7 @@
 package io.netty.util.concurrent;
 
 import io.netty.util.internal.ObjectUtil;
+import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.SystemPropertyUtil;
 import io.netty.util.internal.UnstableApi;
 import io.netty.util.internal.logging.InternalLogger;
@@ -582,7 +583,18 @@ public abstract class SingleThreadEventExecutor extends AbstractScheduledEventEx
         gracefulShutdownTimeout = unit.toNanos(timeout);
 
         if (oldState == ST_NOT_STARTED) {
-            doStartThread();
+            try {
+                doStartThread();
+            } catch (Throwable cause) {
+                STATE_UPDATER.set(this, ST_TERMINATED);
+                terminationFuture.tryFailure(cause);
+
+                if (!(cause instanceof Exception)) {
+                    // Also rethrow as it may be an OOME for example
+                    PlatformDependent.throwException(cause);
+                }
+                return terminationFuture;
+            }
         }
 
         if (wakeup) {
@@ -634,7 +646,18 @@ public abstract class SingleThreadEventExecutor extends AbstractScheduledEventEx
         }
 
         if (oldState == ST_NOT_STARTED) {
-            doStartThread();
+            try {
+                doStartThread();
+            } catch (Throwable cause) {
+                STATE_UPDATER.set(this, ST_TERMINATED);
+                terminationFuture.tryFailure(cause);
+
+                if (!(cause instanceof Exception)) {
+                    // Also rethrow as it may be an OOME for example
+                    PlatformDependent.throwException(cause);
+                }
+                return;
+            }
         }
 
         if (wakeup) {
@@ -837,7 +860,12 @@ public abstract class SingleThreadEventExecutor extends AbstractScheduledEventEx
     private void startThread() {
         if (state == ST_NOT_STARTED) {
             if (STATE_UPDATER.compareAndSet(this, ST_NOT_STARTED, ST_STARTED)) {
-                doStartThread();
+                try {
+                    doStartThread();
+                } catch (Throwable cause) {
+                    STATE_UPDATER.set(this, ST_NOT_STARTED);
+                    PlatformDependent.throwException(cause);
+                }
             }
         }
     }

common/src/test/java/io/netty/util/concurrent/SingleThreadEventExecutorTest.java

@@ -21,6 +21,8 @@ import org.junit.Test;
 import java.util.Collections;
 import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.RejectedExecutionException;
 import java.util.concurrent.TimeUnit;
@@ -28,6 +30,48 @@ import java.util.concurrent.atomic.AtomicReference;
 
 public class SingleThreadEventExecutorTest {
 
+    @Test
+    public void testWrappedExecutureIsShutdown() {
+        ExecutorService executorService = Executors.newSingleThreadExecutor();
+
+        SingleThreadEventExecutor executor = new SingleThreadEventExecutor(null, executorService, false) {
+            @Override
+            protected void run() {
+                while (!confirmShutdown()) {
+                    Runnable task = takeTask();
+                    if (task != null) {
+                        task.run();
+                    }
+                }
+            }
+        };
+
+        executorService.shutdownNow();
+        executeShouldFail(executor);
+        executeShouldFail(executor);
+        try {
+            executor.shutdownGracefully().syncUninterruptibly();
+            Assert.fail();
+        } catch (RejectedExecutionException expected) {
+            // expected
+        }
+        Assert.assertTrue(executor.isShutdown());
+    }
+
+    private static void executeShouldFail(Executor executor) {
+        try {
+            executor.execute(new Runnable() {
+                @Override
+                public void run() {
+                    // Noop.
+                }
+            });
+            Assert.fail();
+        } catch (RejectedExecutionException expected) {
+            // expected
+        }
+    }
+
     @Test
     public void testThreadProperties() {
         final AtomicReference<Thread> threadRef = new AtomicReference<Thread>();