Avoid CancellationException construction in DefaultPromise (#9534)

Motivation

problem with Throwable#addSuppressed() raised in #9151. This introduced
a performance issue when promises are cancelled at a high frequency due
to the construction cost of CancellationException at the time that
DefaultPromise#cancel() is called.

Modifications

- Reinstate the prior static CANCELLATION_CAUSE_HOLDER but use it just
as a sentinel to indicate cancellation, constructing a new
CancellationException only if/when one needs to be explicitly
returned/thrown
- Subclass CancellationException, overriding fillInStackTrace() to
minimize the construction cost in these cases

Result

Promises are much cheaper to cancel. Fixes #9522.

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

@@ -19,6 +19,7 @@ import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.PlatformDependent;
 import io.netty.util.internal.StringUtil;
 import io.netty.util.internal.SystemPropertyUtil;
+import io.netty.util.internal.ThrowableUtil;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -41,6 +42,9 @@ public class DefaultPromise<V> implements Promise<V> {
             AtomicReferenceFieldUpdater.newUpdater(DefaultPromise.class, Object.class, "result");
     private static final Object SUCCESS = new Object();
     private static final Object UNCANCELLABLE = new Object();
+    private static final CauseHolder CANCELLATION_CAUSE_HOLDER = new CauseHolder(ThrowableUtil.unknownStackTrace(
+            new CancellationException(), DefaultPromise.class, "cancel(...)"));
+    private static final StackTraceElement[] CANCELLATION_STACK = CANCELLATION_CAUSE_HOLDER.cause.getStackTrace();
 
     private volatile Object result;
     private final EventExecutor executor;
@@ -124,10 +128,32 @@ public class DefaultPromise<V> implements Promise<V> {
         return result == null;
     }
 
+    private static final class LeanCancellationException extends CancellationException {
+        private static final long serialVersionUID = 2794674970981187807L;
+
+        @Override
+        public Throwable fillInStackTrace() {
+            setStackTrace(CANCELLATION_STACK);
+            return this;
+        }
+
+        @Override
+        public String toString() {
+            return CancellationException.class.getName();
+        }
+    }
+
     @Override
     public Throwable cause() {
         Object result = this.result;
-        return (result instanceof CauseHolder) ? ((CauseHolder) result).cause : null;
+        if (result != CANCELLATION_CAUSE_HOLDER) {
+            return (result instanceof CauseHolder) ? ((CauseHolder) result).cause : null;
+        }
+        CancellationException ce = new LeanCancellationException();
+        if (RESULT_UPDATER.compareAndSet(this, CANCELLATION_CAUSE_HOLDER, new CauseHolder(ce))) {
+            return ce;
+        }
+        return ((CauseHolder) this.result).cause;
     }
 
     @Override
@@ -294,8 +320,7 @@ public class DefaultPromise<V> implements Promise<V> {
      */
     @Override
     public boolean cancel(boolean mayInterruptIfRunning) {
-        if (RESULT_UPDATER.get(this) == null &&
-                RESULT_UPDATER.compareAndSet(this, null, new CauseHolder(new CancellationException()))) {
+        if (RESULT_UPDATER.compareAndSet(this, null, CANCELLATION_CAUSE_HOLDER)) {
             if (checkNotifyWaiters()) {
                 notifyListeners();
             }

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

@@ -38,6 +38,7 @@ import java.util.concurrent.TimeoutException;
 import java.util.concurrent.atomic.AtomicInteger;
 
 import static java.lang.Math.max;
+import static org.hamcrest.Matchers.instanceOf;
 import static org.hamcrest.Matchers.lessThan;
 import static org.junit.Assert.*;
 
@@ -71,7 +72,7 @@ public class DefaultPromiseTest {
         Mockito.when(executor.inEventLoop()).thenReturn(false);
 
         Promise<Void> promise = new DefaultPromise<Void>(executor);
-        promise.cancel(false);
+        assertTrue(promise.cancel(false));
         Mockito.verify(executor, Mockito.never()).execute(Mockito.any(Runnable.class));
         assertTrue(promise.isCancelled());
     }
@@ -103,7 +104,7 @@ public class DefaultPromiseTest {
     @Test(expected = CancellationException.class)
     public void testCancellationExceptionIsThrownWhenBlockingGet() throws InterruptedException, ExecutionException {
         final Promise<Void> promise = new DefaultPromise<>(ImmediateEventExecutor.INSTANCE);
-        promise.cancel(false);
+        assertTrue(promise.cancel(false));
         promise.get();
     }
 
@@ -111,10 +112,18 @@ public class DefaultPromiseTest {
     public void testCancellationExceptionIsThrownWhenBlockingGetWithTimeout() throws InterruptedException,
             ExecutionException, TimeoutException {
         final Promise<Void> promise = new DefaultPromise<>(ImmediateEventExecutor.INSTANCE);
-        promise.cancel(false);
+        assertTrue(promise.cancel(false));
         promise.get(1, TimeUnit.SECONDS);
     }
 
+    @Test
+    public void testCancellationExceptionIsReturnedAsCause() throws InterruptedException,
+    ExecutionException, TimeoutException {
+        final Promise<Void> promise = new DefaultPromise<>(ImmediateEventExecutor.INSTANCE);
+        assertTrue(promise.cancel(false));
+        assertThat(promise.cause(), instanceOf(CancellationException.class));
+    }
+
     @Test
     public void testStackOverflowWithImmediateEventExecutorA() throws Exception {
         testStackOverFlowChainedFuturesA(stackOverflowTestDepth(), ImmediateEventExecutor.INSTANCE, true);