/*
    * Copyright 2024 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   https://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package io.netty.channel.nio;
  
  import io.netty.channel.ChannelException;
  import io.netty.channel.DefaultSelectStrategyFactory;
  import io.netty.channel.IoHandlerContext;
  import io.netty.channel.IoHandle;
  import io.netty.channel.IoHandler;
  import io.netty.channel.IoHandlerFactory;
  import io.netty.channel.IoOps;
  import io.netty.channel.IoRegistration;
  import io.netty.channel.SelectStrategy;
  import io.netty.channel.SelectStrategyFactory;
  import io.netty.util.IntSupplier;
  import io.netty.util.concurrent.ThreadAwareExecutor;
  import io.netty.util.internal.ObjectUtil;
  import io.netty.util.internal.PlatformDependent;
  import io.netty.util.internal.ReflectionUtil;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.SystemPropertyUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.io.IOException;
  import java.lang.reflect.Field;
  import java.nio.channels.CancelledKeyException;
  import java.nio.channels.Selector;
  import java.nio.channels.SelectionKey;
  
  import java.nio.channels.spi.SelectorProvider;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Iterator;
  import java.util.Set;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  
  /**
   * {@link IoHandler} implementation which register the {@link IoHandle}'s to a {@link Selector}.
   */
  public final class NioIoHandler implements IoHandler {
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioIoHandler.class);
  
      private static final int CLEANUP_INTERVAL = 256; // XXX Hard-coded value, but won't need customization.
  
      private static final boolean DISABLE_KEY_SET_OPTIMIZATION =
              SystemPropertyUtil.getBoolean("io.netty.noKeySetOptimization", false);
  
      private static final int MIN_PREMATURE_SELECTOR_RETURNS = 3;
      private static final int SELECTOR_AUTO_REBUILD_THRESHOLD;
  
      private final IntSupplier selectNowSupplier = new IntSupplier() {
          @Override
          public int get() throws Exception {
              return selectNow();
          }
      };
  
      // Workaround for JDK NIO bug.
      //
      // See:
      // - https://bugs.openjdk.java.net/browse/JDK-6427854 for first few dev (unreleased) builds of JDK 7
      // - https://bugs.openjdk.java.net/browse/JDK-6527572 for JDK prior to 5.0u15-rev and 6u10
      // - https://github.com/netty/netty/issues/203
      static {
          int selectorAutoRebuildThreshold = SystemPropertyUtil.getInt("io.netty.selectorAutoRebuildThreshold", 512);
          if (selectorAutoRebuildThreshold < MIN_PREMATURE_SELECTOR_RETURNS) {
              selectorAutoRebuildThreshold = 0;
          }
  
          SELECTOR_AUTO_REBUILD_THRESHOLD = selectorAutoRebuildThreshold;
  
          if (logger.isDebugEnabled()) {
              logger.debug("-Dio.netty.noKeySetOptimization: {}", DISABLE_KEY_SET_OPTIMIZATION);
              logger.debug("-Dio.netty.selectorAutoRebuildThreshold: {}", SELECTOR_AUTO_REBUILD_THRESHOLD);
          }
      }
  
      /**
       * The NIO {@link Selector}.
       */
      private Selector selector;
     private Selector unwrappedSelector;
     private SelectedSelectionKeySet selectedKeys;
 
     private final SelectorProvider provider;
 
     /**
      * Boolean that controls determines if a blocked Selector.select should
      * break out of its selection process. In our case we use a timeout for
      * the select method and the select method will block for that time unless
      * waken up.
      */
     private final AtomicBoolean wakenUp = new AtomicBoolean();
 
     private final SelectStrategy selectStrategy;
     private final ThreadAwareExecutor executor;
     private int cancelledKeys;
     private boolean needsToSelectAgain;
 
     private NioIoHandler(ThreadAwareExecutor executor, SelectorProvider selectorProvider,
                          SelectStrategy strategy) {
         this.executor = ObjectUtil.checkNotNull(executor, "executionContext");
         this.provider = ObjectUtil.checkNotNull(selectorProvider, "selectorProvider");
         this.selectStrategy = ObjectUtil.checkNotNull(strategy, "selectStrategy");
         final SelectorTuple selectorTuple = openSelector();
         this.selector = selectorTuple.selector;
         this.unwrappedSelector = selectorTuple.unwrappedSelector;
     }
 
     private static final class SelectorTuple {
         final Selector unwrappedSelector;
         final Selector selector;
 
         SelectorTuple(Selector unwrappedSelector) {
             this.unwrappedSelector = unwrappedSelector;
             this.selector = unwrappedSelector;
         }
 
         SelectorTuple(Selector unwrappedSelector, Selector selector) {
             this.unwrappedSelector = unwrappedSelector;
             this.selector = selector;
         }
     }
 
     private SelectorTuple openSelector() {
         final Selector unwrappedSelector;
         try {
             unwrappedSelector = provider.openSelector();
         } catch (IOException e) {
             throw new ChannelException("failed to open a new selector", e);
         }
 
         if (DISABLE_KEY_SET_OPTIMIZATION) {
             return new SelectorTuple(unwrappedSelector);
         }
 
         Object maybeSelectorImplClass = AccessController.doPrivileged(new PrivilegedAction<Object>() {
             @Override
             public Object run() {
                 try {
                     return Class.forName(
                             "sun.nio.ch.SelectorImpl",
                             false,
                             PlatformDependent.getSystemClassLoader());
                 } catch (Throwable cause) {
                     return cause;
                 }
             }
         });
 
         if (!(maybeSelectorImplClass instanceof Class) ||
                 // ensure the current selector implementation is what we can instrument.
                 !((Class<?>) maybeSelectorImplClass).isAssignableFrom(unwrappedSelector.getClass())) {
             if (maybeSelectorImplClass instanceof Throwable) {
                 Throwable t = (Throwable) maybeSelectorImplClass;
                 logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, t);
             }
             return new SelectorTuple(unwrappedSelector);
         }
 
         final Class<?> selectorImplClass = (Class<?>) maybeSelectorImplClass;
         final SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet();
 
         Object maybeException = AccessController.doPrivileged(new PrivilegedAction<Object>() {
             @Override
             public Object run() {
                 try {
                     Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
                     Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");
 
                     if (PlatformDependent.javaVersion() >= 9 && PlatformDependent.hasUnsafe()) {
                         // Let us try to use sun.misc.Unsafe to replace the SelectionKeySet.
                         // This allows us to also do this in Java9+ without any extra flags.
                         long selectedKeysFieldOffset = PlatformDependent.objectFieldOffset(selectedKeysField);
                         long publicSelectedKeysFieldOffset =
                                 PlatformDependent.objectFieldOffset(publicSelectedKeysField);
 
                         if (selectedKeysFieldOffset != -1 && publicSelectedKeysFieldOffset != -1) {
                             PlatformDependent.putObject(
                                     unwrappedSelector, selectedKeysFieldOffset, selectedKeySet);
                             PlatformDependent.putObject(
                                     unwrappedSelector, publicSelectedKeysFieldOffset, selectedKeySet);
                             return null;
                         }
                         // We could not retrieve the offset, lets try reflection as last-resort.
                     }
 
                     Throwable cause = ReflectionUtil.trySetAccessible(selectedKeysField, true);
                     if (cause != null) {
                         return cause;
                     }
                     cause = ReflectionUtil.trySetAccessible(publicSelectedKeysField, true);
                     if (cause != null) {
                         return cause;
                     }
 
                     selectedKeysField.set(unwrappedSelector, selectedKeySet);
                     publicSelectedKeysField.set(unwrappedSelector, selectedKeySet);
                     return null;
                 } catch (NoSuchFieldException | IllegalAccessException e) {
                     return e;
                 }
             }
         });
 
         if (maybeException instanceof Exception) {
             selectedKeys = null;
             Exception e = (Exception) maybeException;
             logger.trace("failed to instrument a special java.util.Set into: {}", unwrappedSelector, e);
             return new SelectorTuple(unwrappedSelector);
         }
         selectedKeys = selectedKeySet;
         logger.trace("instrumented a special java.util.Set into: {}", unwrappedSelector);
         return new SelectorTuple(unwrappedSelector,
                 new SelectedSelectionKeySetSelector(unwrappedSelector, selectedKeySet));
     }
 
     /**
      * Returns the {@link SelectorProvider} used by this {@link NioEventLoop} to obtain the {@link Selector}.
      */
     public SelectorProvider selectorProvider() {
         return provider;
     }
 
     Selector selector() {
         return selector;
     }
 
     int numRegistered() {
         return selector().keys().size() - cancelledKeys;
     }
 
     Set<SelectionKey> registeredSet() {
         return selector().keys();
     }
 
     void rebuildSelector0() {
         final Selector oldSelector = selector;
         final SelectorTuple newSelectorTuple;
 
         if (oldSelector == null) {
             return;
         }
 
         try {
             newSelectorTuple = openSelector();
         } catch (Exception e) {
             logger.warn("Failed to create a new Selector.", e);
             return;
         }
 
         // Register all channels to the new Selector.
         int nChannels = 0;
         for (SelectionKey key : oldSelector.keys()) {
             DefaultNioRegistration handle = (DefaultNioRegistration) key.attachment();
             try {
                 if (!key.isValid() || key.channel().keyFor(newSelectorTuple.unwrappedSelector) != null) {
                     continue;
                 }
 
                 handle.register(newSelectorTuple.unwrappedSelector);
                 nChannels++;
             } catch (Exception e) {
                 logger.warn("Failed to re-register a NioHandle to the new Selector.", e);
                 handle.cancel();
             }
         }
 
         selector = newSelectorTuple.selector;
         unwrappedSelector = newSelectorTuple.unwrappedSelector;
 
         try {
             // time to close the old selector as everything else is registered to the new one
             oldSelector.close();
         } catch (Throwable t) {
             if (logger.isWarnEnabled()) {
                 logger.warn("Failed to close the old Selector.", t);
             }
         }
 
         if (logger.isInfoEnabled()) {
             logger.info("Migrated " + nChannels + " channel(s) to the new Selector.");
         }
     }
 
     private static NioIoHandle nioHandle(IoHandle handle) {
         if (handle instanceof NioIoHandle) {
             return (NioIoHandle) handle;
         }
         throw new IllegalArgumentException("IoHandle of type " + StringUtil.simpleClassName(handle) + " not supported");
     }
 
     private static NioIoOps cast(IoOps ops) {
         if (ops instanceof NioIoOps) {
             return (NioIoOps) ops;
         }
         throw new IllegalArgumentException("IoOps of type " + StringUtil.simpleClassName(ops) + " not supported");
     }
 
     final class DefaultNioRegistration implements IoRegistration {
         private final AtomicBoolean canceled = new AtomicBoolean();
         private final NioIoHandle handle;
         private volatile SelectionKey key;
 
         DefaultNioRegistration(ThreadAwareExecutor executor, NioIoHandle handle, NioIoOps initialOps, Selector selector)
                 throws IOException {
             this.handle = handle;
             key = handle.selectableChannel().register(selector, initialOps.value, this);
         }
 
         NioIoHandle handle() {
             return handle;
         }
 
         void register(Selector selector) throws IOException {
             SelectionKey newKey = handle.selectableChannel().register(selector, key.interestOps(), this);
             key.cancel();
             key = newKey;
         }
 
         @SuppressWarnings("unchecked")
         @Override
         public <T> T attachment() {
             return (T) key;
         }
 
         @Override
         public boolean isValid() {
             return !canceled.get() && key.isValid();
         }
 
         @Override
         public long submit(IoOps ops) {
             int v = cast(ops).value;
             key.interestOps(v);
             return v;
         }
 
         @Override
         public boolean cancel() {
             if (!canceled.compareAndSet(false, true)) {
                 return false;
             }
             key.cancel();
             cancelledKeys++;
             if (cancelledKeys >= CLEANUP_INTERVAL) {
                 cancelledKeys = 0;
                 needsToSelectAgain = true;
             }
             return true;
         }
 
         void close() {
             cancel();
             try {
                 handle.close();
             } catch (Exception e) {
                 logger.debug("Exception during closing " + handle, e);
             }
         }
 
         void handle(int ready) {
             handle.handle(this, NioIoOps.eventOf(ready));
         }
     }
 
     @Override
     public IoRegistration register(IoHandle handle)
             throws Exception {
         NioIoHandle nioHandle = nioHandle(handle);
         NioIoOps ops = NioIoOps.NONE;
         boolean selected = false;
         for (;;) {
             try {
                 return new DefaultNioRegistration(executor, nioHandle, ops, unwrappedSelector());
             } catch (CancelledKeyException e) {
                 if (!selected) {
                     // Force the Selector to select now as the "canceled" SelectionKey may still be
                     // cached and not removed because no Select.select(..) operation was called yet.
                     selectNow();
                     selected = true;
                 } else {
                     // We forced a select operation on the selector before but the SelectionKey is still cached
                     // for whatever reason. JDK bug ?
                     throw e;
                 }
             }
         }
     }
 
     @Override
     public int run(IoHandlerContext context) {
         int handled = 0;
         try {
             try {
                 switch (selectStrategy.calculateStrategy(selectNowSupplier, !context.canBlock())) {
                     case SelectStrategy.CONTINUE:
                         return 0;
 
                     case SelectStrategy.BUSY_WAIT:
                         // fall-through to SELECT since the busy-wait is not supported with NIO
 
                     case SelectStrategy.SELECT:
                         select(context, wakenUp.getAndSet(false));
 
                         // 'wakenUp.compareAndSet(false, true)' is always evaluated
                         // before calling 'selector.wakeup()' to reduce the wake-up
                         // overhead. (Selector.wakeup() is an expensive operation.)
                         //
                         // However, there is a race condition in this approach.
                         // The race condition is triggered when 'wakenUp' is set to
                         // true too early.
                         //
                         // 'wakenUp' is set to true too early if:
                         // 1) Selector is waken up between 'wakenUp.set(false)' and
                         //    'selector.select(...)'. (BAD)
                         // 2) Selector is waken up between 'selector.select(...)' and
                         //    'if (wakenUp.get()) { ... }'. (OK)
                         //
                         // In the first case, 'wakenUp' is set to true and the
                         // following 'selector.select(...)' will wake up immediately.
                         // Until 'wakenUp' is set to false again in the next round,
                         // 'wakenUp.compareAndSet(false, true)' will fail, and therefore
                         // any attempt to wake up the Selector will fail, too, causing
                         // the following 'selector.select(...)' call to block
                         // unnecessarily.
                         //
                         // To fix this problem, we wake up the selector again if wakenUp
                         // is true immediately after selector.select(...).
                         // It is inefficient in that it wakes up the selector for both
                         // the first case (BAD - wake-up required) and the second case
                         // (OK - no wake-up required).
 
                         if (wakenUp.get()) {
                             selector.wakeup();
                         }
                         // fall through
                     default:
                 }
             } catch (IOException e) {
                 // If we receive an IOException here its because the Selector is messed up. Let's rebuild
                 // the selector and retry. https://github.com/netty/netty/issues/8566
                 rebuildSelector0();
                 handleLoopException(e);
                 return 0;
             }
 
             cancelledKeys = 0;
             needsToSelectAgain = false;
             handled = processSelectedKeys();
         } catch (Error e) {
             throw e;
         } catch (Throwable t) {
             handleLoopException(t);
         }
         return handled;
     }
 
     private static void handleLoopException(Throwable t) {
         logger.warn("Unexpected exception in the selector loop.", t);
 
         // Prevent possible consecutive immediate failures that lead to
         // excessive CPU consumption.
         try {
             Thread.sleep(1000);
         } catch (InterruptedException e) {
             // Ignore.
         }
     }
 
     private int processSelectedKeys() {
         if (selectedKeys != null) {
             return processSelectedKeysOptimized();
         } else {
             return processSelectedKeysPlain(selector.selectedKeys());
         }
     }
 
     @Override
     public void destroy() {
         try {
             selector.close();
         } catch (IOException e) {
             logger.warn("Failed to close a selector.", e);
         }
     }
 
     private int processSelectedKeysPlain(Set<SelectionKey> selectedKeys) {
         // check if the set is empty and if so just return to not create garbage by
         // creating a new Iterator every time even if there is nothing to process.
         // See https://github.com/netty/netty/issues/597
         if (selectedKeys.isEmpty()) {
             return 0;
         }
 
         Iterator<SelectionKey> i = selectedKeys.iterator();
         int handled = 0;
         for (;;) {
             final SelectionKey k = i.next();
             i.remove();
 
             processSelectedKey(k);
             ++handled;
 
             if (!i.hasNext()) {
                 break;
             }
 
             if (needsToSelectAgain) {
                 selectAgain();
                 selectedKeys = selector.selectedKeys();
 
                 // Create the iterator again to avoid ConcurrentModificationException
                 if (selectedKeys.isEmpty()) {
                     break;
                 } else {
                     i = selectedKeys.iterator();
                 }
             }
         }
         return handled;
     }
 
     private int processSelectedKeysOptimized() {
         int handled = 0;
         for (int i = 0; i < selectedKeys.size; ++i) {
             final SelectionKey k = selectedKeys.keys[i];
             // null out entry in the array to allow to have it GC'ed once the Channel close
             // See https://github.com/netty/netty/issues/2363
             selectedKeys.keys[i] = null;
 
             processSelectedKey(k);
             ++handled;
 
             if (needsToSelectAgain) {
                 // null out entries in the array to allow to have it GC'ed once the Channel close
                 // See https://github.com/netty/netty/issues/2363
                 selectedKeys.reset(i + 1);
 
                 selectAgain();
                 i = -1;
             }
         }
         return handled;
     }
 
     private void processSelectedKey(SelectionKey k) {
         final DefaultNioRegistration registration = (DefaultNioRegistration) k.attachment();
         if (!registration.isValid()) {
             try {
                 registration.handle.close();
             } catch (Exception e) {
                 logger.debug("Exception during closing " + registration.handle, e);
             }
             return;
         }
         registration.handle(k.readyOps());
     }
 
     @Override
     public void prepareToDestroy() {
         selectAgain();
         Set<SelectionKey> keys = selector.keys();
         Collection<DefaultNioRegistration> registrations = new ArrayList<>(keys.size());
         for (SelectionKey k: keys) {
             DefaultNioRegistration handle = (DefaultNioRegistration) k.attachment();
             registrations.add(handle);
         }
 
         for (DefaultNioRegistration reg: registrations) {
             reg.close();
         }
     }
 
     @Override
     public void wakeup() {
         if (!executor.isExecutorThread(Thread.currentThread()) && wakenUp.compareAndSet(false, true)) {
             selector.wakeup();
         }
     }
 
     @Override
     public boolean isCompatible(Class<? extends IoHandle> handleType) {
         return NioIoHandle.class.isAssignableFrom(handleType);
     }
 
     Selector unwrappedSelector() {
         return unwrappedSelector;
     }
 
     private void select(IoHandlerContext runner, boolean oldWakenUp) throws IOException {
         Selector selector = this.selector;
         try {
             int selectCnt = 0;
             long currentTimeNanos = System.nanoTime();
             long selectDeadLineNanos = currentTimeNanos + runner.delayNanos(currentTimeNanos);
 
             for (;;) {
                 long timeoutMillis = (selectDeadLineNanos - currentTimeNanos + 500000L) / 1000000L;
                 if (timeoutMillis <= 0) {
                     if (selectCnt == 0) {
                         selector.selectNow();
                         selectCnt = 1;
                     }
                     break;
                 }
 
                 // If a task was submitted when wakenUp value was true, the task didn't get a chance to call
                 // Selector#wakeup. So we need to check task queue again before executing select operation.
                 // If we don't, the task might be pended until select operation was timed out.
                 // It might be pended until idle timeout if IdleStateHandler existed in pipeline.
                 if (!runner.canBlock() && wakenUp.compareAndSet(false, true)) {
                     selector.selectNow();
                     selectCnt = 1;
                     break;
                 }
 
                 int selectedKeys = selector.select(timeoutMillis);
                 selectCnt ++;
 
                 if (selectedKeys != 0 || oldWakenUp || wakenUp.get() || !runner.canBlock()) {
                     // - Selected something,
                     // - waken up by user, or
                     // - the task queue has a pending task.
                     // - a scheduled task is ready for processing
                     break;
                 }
                 if (Thread.interrupted()) {
                     // Thread was interrupted so reset selected keys and break so we not run into a busy loop.
                     // As this is most likely a bug in the handler of the user or it's client library we will
                     // also log it.
                     //
                     // See https://github.com/netty/netty/issues/2426
                     if (logger.isDebugEnabled()) {
                         logger.debug("Selector.select() returned prematurely because " +
                                 "Thread.currentThread().interrupt() was called. Use " +
                                 "NioHandler.shutdownGracefully() to shutdown the NioHandler.");
                     }
                     selectCnt = 1;
                     break;
                 }
 
                 long time = System.nanoTime();
                 if (time - TimeUnit.MILLISECONDS.toNanos(timeoutMillis) >= currentTimeNanos) {
                     // timeoutMillis elapsed without anything selected.
                     selectCnt = 1;
                 } else if (SELECTOR_AUTO_REBUILD_THRESHOLD > 0 &&
                         selectCnt >= SELECTOR_AUTO_REBUILD_THRESHOLD) {
                     // The code exists in an extra method to ensure the method is not too big to inline as this
                     // branch is not very likely to get hit very frequently.
                     selector = selectRebuildSelector(selectCnt);
                     selectCnt = 1;
                     break;
                 }
 
                 currentTimeNanos = time;
             }
 
             if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS) {
                 if (logger.isDebugEnabled()) {
                     logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.",
                             selectCnt - 1, selector);
                 }
             }
         } catch (CancelledKeyException e) {
             if (logger.isDebugEnabled()) {
                 logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?",
                         selector, e);
             }
             // Harmless exception - log anyway
         }
     }
 
     int selectNow() throws IOException {
         try {
             return selector.selectNow();
         } finally {
             // restore wakeup state if needed
             if (wakenUp.get()) {
                 selector.wakeup();
             }
         }
     }
 
     private Selector selectRebuildSelector(int selectCnt) throws IOException {
         // The selector returned prematurely many times in a row.
         // Rebuild the selector to work around the problem.
         logger.warn(
                 "Selector.select() returned prematurely {} times in a row; rebuilding Selector {}.",
                 selectCnt, selector);
 
         rebuildSelector0();
         Selector selector = this.selector;
 
         // Select again to populate selectedKeys.
         selector.selectNow();
         return selector;
     }
 
     private void selectAgain() {
         needsToSelectAgain = false;
         try {
             selector.selectNow();
         } catch (Throwable t) {
             logger.warn("Failed to update SelectionKeys.", t);
         }
     }
 
     /**
      * Returns a new {@link IoHandlerFactory} that creates {@link NioIoHandler} instances
      *
      * @return factory                  the {@link IoHandlerFactory}.
      */
     public static IoHandlerFactory newFactory() {
         return newFactory(SelectorProvider.provider(), DefaultSelectStrategyFactory.INSTANCE);
     }
 
     /**
      * Returns a new {@link IoHandlerFactory} that creates {@link NioIoHandler} instances.
      *
      * @param selectorProvider          the {@link SelectorProvider} to use.
      * @return factory                  the {@link IoHandlerFactory}.
      */
     public static IoHandlerFactory newFactory(SelectorProvider selectorProvider) {
         return newFactory(selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
     }
 
     /**
      * Returns a new {@link IoHandlerFactory} that creates {@link NioIoHandler} instances.
      *
      * @param selectorProvider          the {@link SelectorProvider} to use.
      * @param selectStrategyFactory     the {@link SelectStrategyFactory} to use.
      * @return factory                  the {@link IoHandlerFactory}.
      */
     public static IoHandlerFactory newFactory(final SelectorProvider selectorProvider,
                                               final SelectStrategyFactory selectStrategyFactory) {
         ObjectUtil.checkNotNull(selectorProvider, "selectorProvider");
         ObjectUtil.checkNotNull(selectStrategyFactory, "selectStrategyFactory");
         return context ->  new NioIoHandler(context, selectorProvider, selectStrategyFactory.newSelectStrategy());
     }
 }