溫馨提示×
您好，登錄后才能下訂單哦！
點(diǎn)擊 登錄注冊(cè) 即表示同意《億速云用戶服務(wù)條款》
您好，登錄后才能下訂單哦！
Netty代碼下載和編譯參考前一篇Netty文章
https://blog.51cto.com/483181/2112163
一般Netty服務(wù)器端這樣編寫
EventLoopGroup bossGroup = new NioEventLoopGroup(); //1. 實(shí)例化NioEventLoopGroup對(duì)象
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap(); //2.
b.group(bossGroup, workerGroup) //3.
.channel(NioServerSocketChannel.class)
.option(ChannelOption.SO_BACKLOG, 100)
.handler(new LoggingHandler(LogLevel.INFO))
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new FixedLengthFrameDecoder(20));
}
});
ChannelFuture f = b.bind(port).sync(); //4.
f.channel().closeFuture().sync();
} catch (Exception e) {
e.printStackTrace();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
一步步來(lái)看，首先看第一個(gè)注釋，初始化NioEventLoopGroup對(duì)象
EventLoopGroup bossGroup = new NioEventLoopGroup(); //1. 實(shí)例化NioEventLoopGroup對(duì)象下圖是NioEventLoopGroup的類繼承圖，包含類成員和方法，比較詳細(xì)。 這個(gè)功能是IntelliJ 自帶的。
右擊NioEventLoopGroup類名，選擇Diagrams->Show Diagram->上面有f，m的按鈕，分別對(duì)應(yīng)field和method。
如下：
public NioEventLoopGroup() {
this(0);
}
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());
}
我們可以看到幾點(diǎn)
private static SelectorProvider provider = null;
public static SelectorProvider provider() {
synchronized (lock) {
if (provider != null)
return provider;
return AccessController.doPrivileged(
new PrivilegedAction<SelectorProvider>() {
public SelectorProvider run() {
if (loadProviderFromProperty())
return provider;
if (loadProviderAsService())
return provider;
provider = sun.nio.ch.DefaultSelectorProvider.create();
return provider;
}
});
}
}
public class DefaultSelectorProvider {
private DefaultSelectorProvider() {
}
public static SelectorProvider create() {
return new KQueueSelectorProvider();
}
}
public class KQueueSelectorProvider extends SelectorProviderImpl {
public KQueueSelectorProvider() {
}
public AbstractSelector openSelector() throws IOException {
return new KQueueSelectorImpl(this);
}
}
這段代碼我們也可以看到幾點(diǎn):
這個(gè)先記下來(lái)，也許后面分析會(huì)有用，繼續(xù)分析MultithreadEventLoopGroup的構(gòu)造函數(shù)。
protected MultithreadEventLoopGroup(int nThreads, ThreadFactory threadFactory, Object... args) {
super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, threadFactory, args);
}
private static final int DEFAULT_EVENT_LOOP_THREADS;
static {
DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt(
"io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2));
} 上面這段代碼我們可以看到這幾點(diǎn)：
繼續(xù)父類MultithreadEventExecutorGroup
protected MultithreadEventExecutorGroup(int nThreads, Executor executor,
EventExecutorChooserFactory chooserFactory, Object... args) {
...
children = new EventExecutor[nThreads]; //1. 實(shí)例化children數(shù)組
for (int i = 0; i < nThreads; i ++) { //2. 循環(huán)初始化children
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 {
...
}
}
chooser = chooserFactory.newChooser(children); //3. 實(shí)例化chooser
final FutureListener<Object> terminationListener = new FutureListener<Object>() {
@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);
}上面這段代碼可以從下面幾個(gè)點(diǎn)分析：
private final EventExecutor[] children;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的繼承關(guān)系是這樣的，繼承于SingleThreadEventLoop，別忘了上面我們看到NioEventLoopGroup繼承自MultithreadEventLoopGroup.(看名字是單線程和多線程的區(qū)別？)
繼續(xù)看NioEventLoop的構(gòu)造函數(shù)
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider,
SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler) {
super(parent, executor, false, DEFAULT_MAX_PENDING_TASKS, rejectedExecutionHandler);
provider = selectorProvider;
final SelectorTuple selectorTuple = openSelector();
selector = selectorTuple.selector;
unwrappedSelector = selectorTuple.unwrappedSelector;
selectStrategy = strategy;
}
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_KEYSET_OPTIMIZATION) {
return new SelectorTuple(unwrappedSelector);
}
...
}
從上面這段代碼我們可以看出這幾點(diǎn)
selector, unwrappedSelector是通過(guò)provider.openSelector()打開的.
根據(jù)2.3段的介紹，provider之前介紹的類型是KQueueSelectorProvider，然后它的openSelector會(huì)生成一個(gè)KQueueSelectorImpl
所以provider.openSelector()得到是KQueueSelectorImpl，KQueueSelectorImpl的繼承關(guān)系如下：
繼續(xù)往回看，看MultithreadEventExecutorGroup的構(gòu)造函數(shù)。
EventExecutorChooserFactory.EventExecutorChooser chooser;
protected MultithreadEventExecutorGroup(int nThreads, Executor executor, Object... args) {
this(nThreads, executor, DefaultEventExecutorChooserFactory.INSTANCE, args);
}
chooser = chooserFactory.newChooser(children);上面代碼我們可以看到：
public EventExecutorChooser newChooser(EventExecutor[] executors) {
if (isPowerOfTwo(executors.length)) {
return new PowerOfTwoEventExecutorChooser(executors);
} else {
return new GenericEventExecutorChooser(executors);
}
}public static final DefaultEventExecutorChooserFactory INSTANCE = new DefaultEventExecutorChooserFactory();
繼續(xù)看newChooser的實(shí)現(xiàn)
newChooser的代碼就不貼了，上面就有，從上面代碼可以看到：
private static boolean isPowerOfTwo(int val) {
return (val & -val) == val;
}
private static final class PowerOfTwoEventExecutorChooser implements EventExecutorChooser {
private final AtomicInteger idx = new AtomicInteger();
private final EventExecutor[] executors;
PowerOfTwoEventExecutorChooser(EventExecutor[] executors) {
this.executors = executors;
}
@Override
public EventExecutor next() {
return executors[idx.getAndIncrement() & executors.length - 1];
}
}
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)];
}
} 這種實(shí)現(xiàn)方法感覺比較優(yōu)雅和高效，首先拿到-val，也就是val的二進(jìn)制倒轉(zhuǎn)，然后+1。再做&運(yùn)算。
大家自己可以拿到數(shù)字舉個(gè)例子，比較巧妙。后續(xù)自己寫代碼可以借鑒，這是讀源碼的一個(gè)好處，可以學(xué)習(xí)到別人很多優(yōu)秀的寫法。
但是說(shuō)實(shí)話，我沒(méi)有想到這兩種算法有什么區(qū)別，如果誰(shuí)知道，請(qǐng)告訴我，謝謝。
return executors[idx.getAndIncrement() & executors.length - 1];
return executors[Math.abs(idx.getAndIncrement() % executors.length)];繼續(xù)往回走，MultithreadEventExecutorGroup的構(gòu)造函數(shù)就基本看完了。
我們來(lái)總結(jié)下NioEventLoopGroup的實(shí)例化過(guò)程，可以得到以下幾點(diǎn)。
1. NioEventLoopGroup的父類MultithreadEventExecutorGroup包含一個(gè)NioEventLoop數(shù)組children，數(shù)組的大小等于nThreads線程數(shù)目。如果沒(méi)有指定，默認(rèn)一般是cpu核數(shù) x 2
2. NioEventLoopGroup和NioEventLoop一樣都是繼承自Executor，但是NioEventLoopGroup又包含多個(gè)NioEventLoop(children數(shù)組)，這種關(guān)系有點(diǎn)像android里面ViewGroup和View的關(guān)系?；蛘哐b飾者模式？
3. NioEventLoopGroup繼承自MultithreadEventLoopGroup，而NioEventLoop繼承自SingleThreadEventLoop，從名字看，不知道和多線程，單線程有沒(méi)有關(guān)系。
4. MultithreadEventLoopGroup有個(gè)chooser，執(zhí)行next方法的時(shí)候，會(huì)選擇下一個(gè)NioEventLoop對(duì)象，雖然并不知道兩個(gè)chooser算法有何區(qū)別。
5. NioEventLoopGroup里面重寫了newChild方法，里面實(shí)例化NioEventLoop。
6. NioEventLoop里面包含了Selector，類型是KQueueSelectorImpl
SelectorProvider provider
SelectStrategy selectStrategy
SelectStrategy這個(gè)我們上面我們沒(méi)有關(guān)注，其實(shí)它是NioEventLoopGroup構(gòu)造函數(shù)傳進(jìn)去的，如下：
public NioEventLoopGroup(
int nThreads, Executor executor, final SelectorProvider selectorProvider) {
this(nThreads, executor, selectorProvider, DefaultSelectStrategyFactory.INSTANCE);
}
public final class DefaultSelectStrategyFactory implements SelectStrategyFactory {
public static final SelectStrategyFactory INSTANCE = new DefaultSelectStrategyFactory();
private DefaultSelectStrategyFactory() { }
@Override
public SelectStrategy newSelectStrategy() {
return DefaultSelectStrategy.INSTANCE;
}
}
final class DefaultSelectStrategy implements SelectStrategy {
static final SelectStrategy INSTANCE = new DefaultSelectStrategy();
private DefaultSelectStrategy() { }
@Override
public int calculateStrategy(IntSupplier selectSupplier, boolean hasTasks) throws Exception {
return hasTasks ? selectSupplier.get() : SelectStrategy.SELECT;
}
}所以SelectStrategy的實(shí)現(xiàn)類是DefaultSelectStrategy.
在理清楚NioEventLoopGroup實(shí)例化的過(guò)程之后，我們下一篇繼續(xù)按照源代碼分析Netty服務(wù)器端的源代碼。
免責(zé)聲明：本站發(fā)布的內(nèi)容（圖片、視頻和文字）以原創(chuàng)、轉(zhuǎn)載和分享為主，文章觀點(diǎn)不代表本網(wǎng)站立場(chǎng)，如果涉及侵權(quán)請(qǐng)聯(lián)系站長(zhǎng)郵箱：is@yisu.com進(jìn)行舉報(bào)，并提供相關(guān)證據(jù)，一經(jīng)查實(shí)，將立刻刪除涉嫌侵權(quán)內(nèi)容。
億速云公眾號(hào)
手機(jī)網(wǎng)站二維碼