protected MultithreadEventExecutorGroup(int nThreads, Executor executor, 
                                        EventExecutorChooserFactory chooserFactory, Object... args) {
    //代碼省略
    if (executor == null) {
        //創(chuàng)建一個(gè)新的線程執(zhí)行器(1)
        executor = new ThreadPerTaskExecutor(newDefaultThreadFactory());
    }
    //構(gòu)造NioEventLoop(2)
    children = new EventExecutor[nThreads];
    for (int i = 0; i < nThreads; i ++) {
        boolean success = false;
        try {
            children[i] = newChild(executor, args);
            success = true;
        } catch (Exception e) {
            throw new IllegalStateException("failed to create a child event loop", e);
        } finally {
           //代碼省略
        }
    }
    //創(chuàng)建線程選擇器(3)
    chooser = chooserFactory.newChooser(children);
    //代碼省略
}

我們看第三步, 創(chuàng)建線程選擇器:

chooser = chooserFactory.newChooser(children);

NioEventLoop都綁定一個(gè)chooser對(duì)象, 作為線程選擇器, 通過這個(gè)線程選擇器, 為每一個(gè)channel分配不同的線程

我們看到newChooser(children)傳入了NioEventLoop數(shù)組

我們跟到DefaultEventExecutorChooserFactory類中的newChooser方法:

public EventExecutorChooser newChooser(EventExecutor[] executors) { 
    if (isPowerOfTwo(executors.length)) { 
        return new PowerOfTowEventExecutorChooser(executors);
    } else {
        return new GenericEventExecutorChooser(executors);
    }
}

這里通過 isPowerOfTwo(executors.length) 判斷NioEventLoop的線程數(shù)是不是2的倍數(shù), 然后根據(jù)判斷結(jié)果返回兩種選擇器對(duì)象, 這里使用到j(luò)ava設(shè)計(jì)模式的策略模式

根據(jù)這兩個(gè)類的名字不難看出, 如果是2的倍數(shù), 使用的是一種高性能的方式選擇線程, 如果不是2的倍數(shù), 則使用一種比較普通的線程選擇方式

我們簡單跟進(jìn)這兩種策略的選擇器對(duì)象中看一下, 首先看一下PowerOfTowEventExecutorChooser這個(gè)類:

private static final class PowerOfTowEventExecutorChooser implements EventExecutorChooser {
    private final AtomicInteger idx = new AtomicInteger();
    private final EventExecutor[] executors;
    PowerOfTowEventExecutorChooser(EventExecutor[] executors) {
        this.executors = executors;
    }
    @Override
    public EventExecutor next() {
        return executors[idx.getAndIncrement() & executors.length - 1];
    }
}

這個(gè)類實(shí)現(xiàn)了線程選擇器的接口EventExecutorChooser, 構(gòu)造方法中初始化了NioEventLoop線程數(shù)組

重點(diǎn)關(guān)注下next()方法, next()方法就是選擇下一個(gè)線程的方法, 如果線程數(shù)是2的倍數(shù), 這里通過按位與進(jìn)行計(jì)算, 所以效率極高

再看一下GenericEventExecutorChooser這個(gè)類:

private static final class GenericEventExecutorChooser implements EventExecutorChooser {
    private final AtomicInteger idx = new AtomicInteger();
    private final EventExecutor[] executors;
    GenericEventExecutorChooser(EventExecutor[] executors) {
        this.executors = executors;
    }
    @Override
    public EventExecutor next() {
        return executors[Math.abs(idx.getAndIncrement() % executors.length)];
    }
}

這個(gè)類同樣實(shí)現(xiàn)了線程選擇器的接口EventExecutorChooser, 并在造方法中初始化了NioEventLoop線程數(shù)組

再看這個(gè)類的next()方法, 如果線程數(shù)不是2的倍數(shù), 則用絕對(duì)值和取模的這種效率一般的方式進(jìn)行線程選擇

這樣, 我們就初始化了線程選擇器對(duì)象

以上就是Netty源碼分析NioEventLoop初始化線程選擇器創(chuàng)建的詳細(xì)內(nèi)容，更多關(guān)于Netty線程選擇器NioEventLoop的資料請(qǐng)關(guān)注腳本之家其它相關(guān)文章！

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