Use static exceptions for closing websocket flushers.

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/exception/SentinelWebSocketCloseException.java

@@ -0,0 +1,32 @@
+//
+// ========================================================================
+// Copyright (c) 1995-2022 Mort Bay Consulting Pty Ltd and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
+// which is available at https://www.apache.org/licenses/LICENSE-2.0.
+//
+// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
+// ========================================================================
+//
+
+package org.eclipse.jetty.websocket.core.exception;
+
+/**
+ * Suppressed exceptions are disabled for this implementation,
+ * meaning calling {@link #addSuppressed(Throwable)} has no effect.
+ * This means instances of {@link SentinelWebSocketCloseException} are suitable to be kept as static fields.
+ */
+public class SentinelWebSocketCloseException extends Exception
+{
+    public SentinelWebSocketCloseException()
+    {
+        this(null);
+    }
+
+    public SentinelWebSocketCloseException(String message)
+    {
+        super(message, null, false, true);
+    }
+}

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/internal/DemandingFlusher.java

@@ -23,6 +23,7 @@
 import org.eclipse.jetty.websocket.core.Extension;
 import org.eclipse.jetty.websocket.core.Frame;
 import org.eclipse.jetty.websocket.core.IncomingFrames;
+import org.eclipse.jetty.websocket.core.exception.SentinelWebSocketCloseException;
 
 /**
  * <p>This flusher can be used to mutated and fragment {@link Frame}s and forwarded them on towards the application using the
@@ -38,6 +39,8 @@
  */
 public abstract class DemandingFlusher extends IteratingCallback implements DemandChain
 {
+    private static final Throwable SENTINEL_CLOSE_EXCEPTION = new SentinelWebSocketCloseException();
+
     private final IncomingFrames _emitFrame;
     private final AtomicLong _demand = new AtomicLong();
     private final AtomicReference<Throwable> _failure = new AtomicReference<>();
@@ -101,6 +104,18 @@ public void onFrame(Frame frame, Callback callback)
         succeeded();
     }
 
+    /**
+     * Used to close this flusher when there is no explicit failure.
+     */
+    public void closeFlusher()
+    {
+        if (_failure.compareAndSet(null, SENTINEL_CLOSE_EXCEPTION))
+        {
+            failed(SENTINEL_CLOSE_EXCEPTION);
+            iterate();
+        }
+    }
+
     /**
      * Used to fail this flusher possibly from an external event such as a callback.
      * @param t the failure.

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/internal/FrameFlusher.java

@@ -35,6 +35,7 @@
 import org.eclipse.jetty.websocket.core.CloseStatus;
 import org.eclipse.jetty.websocket.core.Frame;
 import org.eclipse.jetty.websocket.core.OpCode;
+import org.eclipse.jetty.websocket.core.exception.SentinelWebSocketCloseException;
 import org.eclipse.jetty.websocket.core.exception.WebSocketException;
 import org.eclipse.jetty.websocket.core.exception.WebSocketWriteTimeoutException;
 import org.slf4j.Logger;
@@ -44,6 +45,7 @@ public class FrameFlusher extends IteratingCallback
 {
     public static final Frame FLUSH_FRAME = new Frame(OpCode.BINARY);
     private static final Logger LOG = LoggerFactory.getLogger(FrameFlusher.class);
+    private static final Throwable CLOSED_CHANNEL = new SentinelWebSocketCloseException();
 
     private final AutoLock lock = new AutoLock();
     private final LongAdder messagesOut = new LongAdder();
@@ -184,15 +186,7 @@ public void onClose(Throwable cause)
     {
         try (AutoLock l = lock.lock())
         {
-            // TODO: find a way to not create exception if cause is null.
-            closedCause = cause == null ? new ClosedChannelException()
-            {
-                @Override
-                public Throwable fillInStackTrace()
-                {
-                    return this;
-                }
-            } : cause;
+            closedCause = cause == null ? CLOSED_CHANNEL : cause;
         }
         iterate();
     }

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/internal/PerMessageDeflateExtension.java

@@ -14,7 +14,6 @@
 package org.eclipse.jetty.websocket.core.internal;
 
 import java.nio.ByteBuffer;
-import java.nio.channels.ClosedChannelException;
 import java.util.HashMap;
 import java.util.Map;
 import java.util.concurrent.atomic.AtomicReference;
@@ -150,17 +149,8 @@ public void init(final ExtensionConfig config, WebSocketComponents components)
     @Override
     public void close()
     {
-        // TODO: use IteratingCallback.close() instead of creating exception with failFlusher methods.
-        ClosedChannelException exception = new ClosedChannelException()
-        {
-            @Override
-            public Throwable fillInStackTrace()
-            {
-                return this;
-            }
-        };
-        incomingFlusher.failFlusher(exception);
-        outgoingFlusher.failFlusher(exception);
+        incomingFlusher.closeFlusher();
+        outgoingFlusher.closeFlusher();
         releaseInflater();
         releaseDeflater();
     }

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/internal/TransformingFlusher.java

@@ -20,6 +20,7 @@
 import org.eclipse.jetty.util.IteratingCallback;
 import org.eclipse.jetty.util.thread.AutoLock;
 import org.eclipse.jetty.websocket.core.Frame;
+import org.eclipse.jetty.websocket.core.exception.SentinelWebSocketCloseException;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -33,6 +34,7 @@
 public abstract class TransformingFlusher
 {
     private final Logger log = LoggerFactory.getLogger(this.getClass());
+    private static final Throwable SENTINEL_CLOSE_EXCEPTION = new SentinelWebSocketCloseException();
 
     private final AutoLock lock = new AutoLock();
     private final Queue<FrameEntry> entries = new ArrayDeque<>();
@@ -77,13 +79,20 @@ public final void sendFrame(Frame frame, Callback callback, boolean batch)
             notifyCallbackFailure(callback, failure);
     }
 
+    /**
+     * Used to close this flusher when there is no explicit failure.
+     */
+    public void closeFlusher()
+    {
+        failFlusher(SENTINEL_CLOSE_EXCEPTION);
+    }
+
     /**
      * Used to fail this flusher possibly from an external event such as a callback.
      * @param t the failure.
      */
     public void failFlusher(Throwable t)
     {
-        // TODO: find a way to close the flusher in non error case without exception.
         boolean failed = false;
         try (AutoLock l = lock.lock())
         {