Netty源码分析-NioEventLoop

 

/*
 * Copyright 2012 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:
 *
 *   http://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.Channel;
import io.netty.channel.ChannelException;
import io.netty.channel.EventLoop;
import io.netty.channel.EventLoopException;
import io.netty.channel.EventLoopTaskQueueFactory;
import io.netty.channel.SelectStrategy;
import io.netty.channel.SingleThreadEventLoop;
import io.netty.util.IntSupplier;
import io.netty.util.concurrent.RejectedExecutionHandler;
import io.netty.util.internal.ObjectUtil;
import io.netty.util.internal.PlatformDependent;
import io.netty.util.internal.ReflectionUtil;
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.SelectableChannel;
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.Queue;
import java.util.Set;
import java.util.concurrent.Executor;
import java.util.concurrent.atomic.AtomicLong;

/**
 * {@link SingleThreadEventLoop} implementation which register the {@link Channel}'s to a
 * {@link Selector} and so does the multi-plexing of these in the event loop.
 *
 */
public final class NioEventLoop extends SingleThreadEventLoop {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(NioEventLoop.class);

    private static final int CLEANUP_INTERVAL = 256; // XXX Hard-coded value, but won't need customization.

    //是否禁止优化JDK原生的selector
    private static final boolean DISABLE_KEY_SET_OPTIMIZATION =
            SystemPropertyUtil.getBoolean("io.netty.noKeySetOptimization", false);

    private static final int MIN_PREMATURE_SELECTOR_RETURNS = 3;

    //默认值512
    private static final int SELECTOR_AUTO_REBUILD_THRESHOLD;

    //调用JDK的selector.selectNow()方法，返回IO事件的数量
    private final IntSupplier selectNowSupplier = new IntSupplier() {
        @Override
        public int get() throws Exception {
            return selectNow();
        }
    };

    // Workaround for JDK NIO bug.
    // 修复JDK空轮询的BUG
    // See:
    // - http://bugs.sun.com/view_bug.do?bug_id=6427854
    // - https://github.com/netty/netty/issues/203
    static {
        final String key = "sun.nio.ch.bugLevel";
        final String bugLevel = SystemPropertyUtil.get(key);
        if (bugLevel == null) {
            try {
                AccessController.doPrivileged(new PrivilegedAction() {
                    @Override
                    public Void run() {
                        System.setProperty(key, "");
                        return null;
                    }
                });
            } catch (final SecurityException e) {
                logger.debug("Unable to get/set System Property: " + key, e);
            }
        }

        //默认值512
        int selectorAutoRebuildThreshold = SystemPropertyUtil.getInt("io.netty.selectorAutoRebuildThreshold", 512);
        if (selectorAutoRebuildThreshold < MIN_PREMATURE_SELECTOR_RETURNS) {
            selectorAutoRebuildThreshold = 0;
        }

        //默认值512
        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}.
     */
    //优化后的事件选择器
    private Selector selector;
    //JDK-NIO的事件选择器
    private Selector unwrappedSelector;
    //优化了Set接口，内部使用数组
    private SelectedSelectionKeySet selectedKeys;

    //NIO的selector创建器
    private final SelectorProvider provider;

    private static final long AWAKE = -1L;
    private static final long NONE = Long.MAX_VALUE;

    // nextWakeupNanos is:
    //    AWAKE            when EL is awake
    //    NONE             when EL is waiting with no wakeup scheduled
    //    other value T    when EL is waiting with wakeup scheduled at time T
    private final AtomicLong nextWakeupNanos = new AtomicLong(AWAKE);

    //默认实现类DefaultSelectStrategy
    private final SelectStrategy selectStrategy;

    //IO使用比率
    private volatile int ioRatio = 50;
    private int cancelledKeys;
    private boolean needsToSelectAgain;

    NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
                 SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler,
                 EventLoopTaskQueueFactory queueFactory) {
        super(parent, executor, false, newTaskQueue(queueFactory), newTaskQueue(queueFactory),
                rejectedExecutionHandler);
        this.provider = ObjectUtil.checkNotNull(selectorProvider, "selectorProvider");
        this.selectStrategy = ObjectUtil.checkNotNull(strategy, "selectStrategy");
        final SelectorTuple selectorTuple = openSelector();
        //优化后的对象
        this.selector = selectorTuple.selector;
        //JDK原生对象
        this.unwrappedSelector = selectorTuple.unwrappedSelector;
    }

    private static Queue newTaskQueue(
            EventLoopTaskQueueFactory queueFactory) {
        if (queueFactory == null) {
            return newTaskQueue0(DEFAULT_MAX_PENDING_TASKS);
        }
        return queueFactory.newTaskQueue(DEFAULT_MAX_PENDING_TASKS);
    }

    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 {
            //JDK原生Selector
            unwrappedSelector = provider.openSelector();
        } catch (IOException e) {
            throw new ChannelException("failed to open a new selector", e);
        }

        //禁止优化JDK原生Selector
        if (DISABLE_KEY_SET_OPTIMIZATION) {
            //封装为SelectorTuple对象，内部原生JDK的Selector
            return new SelectorTuple(unwrappedSelector);
        }

        //反射获取JDK原生Selector的实现类sun.nio.ch.SelectorImpl
        Object maybeSelectorImplClass = AccessController.doPrivileged(new PrivilegedAction