Netty4源碼分析--構造BossGroup和WorkerGroup

BossGroup和WorkerGroup都是NioEventLoopGroup，BossGroup用來處理nio的Accept，Worker處理nio的Read和Write事件

1 構造NioEventLoopGroup

public NioEventLoopGroup(int nThreads) {
        this(nThreads, (Executor) null);
    }

public NioEventLoopGroup(int nThreads, Executor executor) {
        this(nThreads, executor, SelectorProvider.provider());
    } 

public NioEventLoopGroup(
            int nThreads, Executor executor, final SelectorProvider selectorProvider) {
        this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
    }

public NioEventLoopGroup(int nThreads, Executor executor, final SelectorProvider selectorProvider,
                             final SelectStrategyFactory selectStrategyFactory) {
        super(nThreads, executor, selectorProvider, selectStrategyFactory, RejectedExecutionHandlers.reject());
    }

SelectorProvider是java Nio對IO多路復用機制的實現，與OS相關，對於Linux來說，就是利用了linux的epoll

DefaultSelectStrategyFactory

2 構造NioEventLoopGroup的父類MultithreadEventLoopGroup

protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) {
        super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args);
    }

DEFAULT_EVENT_LOOP_THREADS 默認為cpu核數 * 2

3 構造MultithreadEventLoopGroup的父類MultithreadEventExecutorGroup

protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
                                            EventExecutorChooserFactory chooserFactory, Object... args) {
        if (nThreads <= 0) {
            throw new IllegalArgumentException(String.format("nThreads: %d (expected: > 0)", nThreads));
        }

        if (executor == null) {
            executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());①
        }

        children = new EventExecutor[nThreads];

        for (int i = 0; i < nThreads; i ++) {
            boolean success = false;
            try {
                children[i] = newChild(executor, args);②
                success = true;
            } catch (Exception e) {
                // TODO: Think about if this is a good exception type
                throw new IllegalStateException("failed to create a child event loop", e);
            } finally {
                if (!success) {
                    for (int j = 0; j < i; j ++) {
                        children[j].shutdownGracefully();
                    }

                    for (int j = 0; j < i; j ++) {
                        EventExecutor e = children[j];
                        try {
                            while (!e.isTerminated()) {
                                e.awaitTermination(Integer.MAX_VALUE, TimeUnit.SECONDS);
                            }
                        } catch (InterruptedException interrupted) {
                            // Let the caller handle the interruption.
                            Thread.currentThread().interrupt();
                            break;
                        }
                    }
                }
            }
        }

        chooser = chooserFactory.newChooser(children);③

        final FutureListener<Object> terminationListener = new FutureListener<Object>() {④
            @Override
            public void operationComplete(Future<Object> future) throws Exception {
                if (terminatedChildren.incrementAndGet() == children.length) {
                    terminationFuture.setSuccess(null);
                }
            }
        };

        for (EventExecutor e: children) {
            e.terminationFuture().addListener(terminationListener);
        }

        Set<EventExecutor> childrenSet = new LinkedHashSet<EventExecutor>(children.length);
        Collections.addAll(childrenSet, children);
        readonlyChildren = Collections.unmodifiableSet(childrenSet);
    }

① executor--用來創建線程，默認實現ThreadPerTaskExecutor

public final class ThreadPerTaskExecutor implements Executor {
    private final ThreadFactory threadFactory;

    public ThreadPerTaskExecutor(ThreadFactory threadFactory) {
        if (threadFactory == null) {
            throw new NullPointerException("threadFactory");
        }
        this.threadFactory = threadFactory;
    }

    @Override
    public void execute(Runnable command) {
        threadFactory.newThread(command).start();
    }
}

protected ThreadFactory newDefaultThreadFactory() {
        return new DefaultThreadFactory(getClass()/*MultithreadEventExecutorGroup*/);
    }

public DefaultThreadFactory(String poolName, boolean daemon, int priority, ThreadGroup threadGroup) {
        if (poolName == null) {
            throw new NullPointerException("poolName");
        }
        if (priority < Thread.MIN_PRIORITY || priority > Thread.MAX_PRIORITY) {
            throw new IllegalArgumentException(
                    "priority: " + priority + " (expected: Thread.MIN_PRIORITY <= priority <= Thread.MAX_PRIORITY)");
        }

        prefix = poolName + '-' + poolId.incrementAndGet() + '-';
        this.daemon = daemon;
        this.priority = priority;
        this.threadGroup = ObjectUtil.checkNotNull(threadGroup, "threadGroup");
    }

    public DefaultThreadFactory(String poolName, boolean daemon, int priority) {
        this(poolName, daemon, priority, Thread.currentThread().getThreadGroup());
    }

    @Override
    public Thread newThread(Runnable r) {
        Thread t = newThread(new DefaultRunnableDecorator(r), prefix + nextId.incrementAndGet());
        try {
            if (t.isDaemon()) {
                if (!daemon) {
                    t.setDaemon(false);
                }
            } else {
                if (daemon) {
                    t.setDaemon(true);
                }
            }

            if (t.getPriority() != priority) {
                t.setPriority(priority);
            }
        } catch (Exception ignored) {
            // Doesn't matter even if failed to set.
        }
        return t;
    }

② newChild--創建EventLoop

// MultithreadEventExecutorGroup
children[i] = newChild(executor, args);

// NioEventLoopGroup
@Override
    protected EventLoop newChild(Executor executor, Object... args) throws Exception {
        return new NioEventLoop(this, executor, (SelectorProvider) args[0],
            ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
    }

③ chooser--根據EventLoop個數采用power of two方式或是隨機方式，選擇一個Worker EventLoop

④ 對每個EventLoop添加監聽器，何時調用，作用是notifylistener // TODO

3 構造EventLoop--打開一個selector

// NioEventLoopGroup
protected EventLoop newChild(Executor executor, Object... args) throws Exception {
        return new NioEventLoop(this, executor, (SelectorProvider) args[0],
            ((SelectStrategyFactory) args[1]).newSelectStrategy(), (RejectedExecutionHandler) args[2]);
    }

NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
                 SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
        super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
        if (selectorProvider == null) {
            throw new NullPointerException("selectorProvider");
        }
        if (strategy == null) {
            throw new NullPointerException("selectStrategy");
        }
        provider = selectorProvider;
        selector = openSelector();
        selectStrategy = strategy;
    }

private Selector openSelector() {
        final Selector selector;
        try {
            selector = provider.openSelector();
        } catch (IOException e) {
            throw new ChannelException("failed to open a new selector", e);
        }

        if (DISABLE_KEYSET_OPTIMIZATION) {
            return selector;
        }

        try {
            SelectedSelectionKeySet selectedKeySet = new SelectedSelectionKeySet();

            Class<?> selectorImplClass =
                    Class.forName("sun.nio.ch.SelectorImpl", false, PlatformDependent.getSystemClassLoader());

            // Ensure the current selector implementation is what we can instrument.
            if (!selectorImplClass.isAssignableFrom(selector.getClass())) {
                return selector;
            }

            Field selectedKeysField = selectorImplClass.getDeclaredField("selectedKeys");
            Field publicSelectedKeysField = selectorImplClass.getDeclaredField("publicSelectedKeys");

            selectedKeysField.setAccessible(true);
            publicSelectedKeysField.setAccessible(true);

            selectedKeysField.set(selector, selectedKeySet);
            publicSelectedKeysField.set(selector, selectedKeySet);

            selectedKeys = selectedKeySet;
            logger.trace("Instrumented an optimized java.util.Set into: {}", selector);
        } catch (Throwable t) {
            selectedKeys = null;
            logger.trace("Failed to instrument an optimized java.util.Set into: {}", selector, t);
        }

        return selector;
    }

構造NioEventLoop的父類SingleThreadEventLoop

protected SingleThreadEventLoop(EventLoopGroup parent, Executor executor,
                                    boolean addTaskWakesUp, int maxPendingTasks,
                                    RejectedExecutionHandler rejectedExecutionHandler) {
        super(parent, executor, addTaskWakesUp, maxPendingTasks, rejectedExecutionHandler);
    }

構造SingleThreadEventLoop的父類SingleThreadEventExecutor

protected SingleThreadEventExecutor(EventExecutorGroup parent, Executor executor,
                                        boolean addTaskWakesUp, int maxPendingTasks,
                                        RejectedExecutionHandler rejectedHandler) {
        super(parent);
        this.addTaskWakesUp = addTaskWakesUp;
        this.maxPendingTasks = Math.max(16, maxPendingTasks);
        this.executor = ObjectUtil.checkNotNull(executor, "executor");
        taskQueue = newTaskQueue(); // 一個LinkedBlockingQueue，用來存放Task
        rejectedExecutionHandler = ObjectUtil.checkNotNull(rejectedHandler, "rejectedHandler");
    }