本文对Netty源码进行了深入剖析，透过Netty源码来理解Netty框架背后的原理。
Nety源码剖析 下载netty源码https://github.com/netty/netty
导入netty源码直接IDEA导入Maven项目选择 pom.xml 即可。
新建demo项目在example项目下面新建最简单的demo
EventLoop事件循环组（线程组）源码EventLoopGroup 是一组 EventLoop 的抽象，Netty 为了更好的利用多核 CPU 资源，一般会有多
个 EventLoop 同时工作，每个 EventLoop 维护着一个 Selector 实例。
线程组源码流程分析[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-QJVPxCCW-1651644412171)(https://cdn.jsdelivr.net/gh/terwer/upload/img/image-20220502225316981.png)]
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-KmXSKjIt-1651644412171)(https://cdn.jsdelivr.net/gh/terwer/upload/img/image-20220502225836471.png)]
线程组源码主要源码跟踪-
NioEventLoopGroup线程组的创建
static { DEFAULT_EVENT_LOOP_THREADS = Math.max(1, SystemPropertyUtil.getInt( "io.netty.eventLoopThreads", NettyRuntime.availableProcessors() * 2)); if (logger.isDebugEnabled()) { logger.debug("-Dio.netty.eventLoopThreads: {}", DEFAULT_EVENT_LOOP_THREADS); } } protected MultithreadEventLoopGroup(int nThreads, Executor executor, Object... args) { super(nThreads == 0 ? DEFAULT_EVENT_LOOP_THREADS : nThreads, executor, args); } -
NioEventLoop的创建
protected MultithreadEventExecutorGroup(int nThreads, Executor executor, EventExecutorChooserFactory chooserFactory, Object... args) { checkPositive(nThreads, "nThreads"); if (executor == null) { executor = new ThreadPerTaskExecutor(newDefaultThreadFactory()); } 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) { // 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); final FutureListenernewChild方法
@Override protected EventLoop newChild(Executor executor, Object... args) throws Exception { SelectorProvider selectorProvider = (SelectorProvider) args[0]; SelectStrategyFactory selectStrategyFactory = (SelectStrategyFactory) args[1]; RejectedExecutionHandler rejectedExecutionHandler = (RejectedExecutionHandler) args[2]; EventLoopTaskQueueFactory taskQueueFactory = null; EventLoopTaskQueueFactory tailTaskQueueFactory = null; int argsLength = args.length; if (argsLength > 3) { taskQueueFactory = (EventLoopTaskQueueFactory) args[3]; } if (argsLength > 4) { tailTaskQueueFactory = (EventLoopTaskQueueFactory) args[4]; } return new NioEventLoop(this, executor, selectorProvider, selectStrategyFactory.newSelectStrategy(), rejectedExecutionHandler, taskQueueFactory, tailTaskQueueFactory); }NioEventLoop
NioEventLoop(NioEventLoopGroup parent, Executor executor, SelectorProvider selectorProvider, SelectStrategy strategy, RejectedExecutionHandler rejectedExecutionHandler, EventLoopTaskQueueFactory taskQueueFactory, EventLoopTaskQueueFactory tailTaskQueueFactory) { super(parent, executor, false, newTaskQueue(taskQueueFactory), newTaskQueue(tailTaskQueueFactory), rejectedExecutionHandler); this.provider = ObjectUtil.checkNotNull(selectorProvider, "selectorProvider"); this.selectStrategy = ObjectUtil.checkNotNull(strategy, "selectStrategy"); final SelectorTuple selectorTuple = openSelector(); this.selector = selectorTuple.selector; this.unwrappedSelector = selectorTuple.unwrappedSelector; }
[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-jZtYYtwO-1651644412172)(https://cdn.jsdelivr.net/gh/terwer/upload/img/image-20220502234157772.png)]
主要源码跟踪-
initAndRegister
final ChannelFuture initAndRegister() { Channel channel = null; try { channel = channelFactory.newChannel(); init(channel); } catch (Throwable t) { if (channel != null) { // channel can be null if newChannel crashed (eg SocketException("too many open files")) channel.unsafe().closeForcibly(); // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor return new DefaultChannelPromise(channel, GlobalEventExecutor.INSTANCE).setFailure(t); } // as the Channel is not registered yet we need to force the usage of the GlobalEventExecutor return new DefaultChannelPromise(new FailedChannel(), GlobalEventExecutor.INSTANCE).setFailure(t); } ChannelFuture regFuture = config().group().register(channel); if (regFuture.cause() != null) { if (channel.isRegistered()) { channel.close(); } else { channel.unsafe().closeForcibly(); } } // If we are here and the promise is not failed, it's one of the following cases: // 1) If we attempted registration from the event loop, the registration has been completed at this point. // i.e. It's safe to attempt bind() or connect() now because the channel has been registered. // 2) If we attempted registration from the other thread, the registration request has been successfully // added to the event loop's task queue for later execution. // i.e. It's safe to attempt bind() or connect() now: // because bind() or connect() will be executed *after* the scheduled registration task is executed // because register(), bind(), and connect() are all bound to the same thread. return regFuture; } -
init方法
@Override void init(Channel channel) { setChannelOptions(channel, newOptionsArray(), logger); setAttributes(channel, newAttributesArray()); ChannelPipeline p = channel.pipeline(); final EventLoopGroup currentChildGroup = childGroup; final ChannelHandler currentChildHandler = childHandler; final Entry() { @Override public void initChannel(final Channel ch) { final ChannelPipeline pipeline = ch.pipeline(); ChannelHandler handler = config.handler(); if (handler != null) { pipeline.addLast(handler); } ch.eventLoop().execute(new Runnable() { @Override public void run() { pipeline.addLast(new ServerBootstrapAcceptor( ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)); } }); } }); } -
regidter方法
@Override public final void register(EventLoop eventLoop, final ChannelPromise promise) { ObjectUtil.checkNotNull(eventLoop, "eventLoop"); if (isRegistered()) { promise.setFailure(new IllegalStateException("registered to an event loop already")); return; } if (!isCompatible(eventLoop)) { promise.setFailure( new IllegalStateException("incompatible event loop type: " + eventLoop.getClass().getName())); return; } AbstractChannel.this.eventLoop = eventLoop; if (eventLoop.inEventLoop()) { register0(promise); } else { try { eventLoop.execute(new Runnable() { @Override public void run() { register0(promise); } }); } catch (Throwable t) { logger.warn( "Force-closing a channel whose registration task was not accepted by an event loop: {}", AbstractChannel.this, t); closeForcibly(); closeFuture.setClosed(); safeSetFailure(promise, t); } } } -
execute()方法
private void execute(Runnable task, boolean immediate) { boolean inEventLoop = inEventLoop(); addTask(task); if (!inEventLoop) { startThread(); if (isShutdown()) { boolean reject = false; try { if (removeTask(task)) { reject = true; } } catch (UnsupportedOperationException e) { // The task queue does not support removal so the best thing we can do is to just move on and // hope we will be able to pick-up the task before its completely terminated. // In worst case we will log on termination. } if (reject) { reject(); } } } if (!addTaskWakesUp && immediate) { wakeup(inEventLoop); } } -
startThread的run方法
for (;;) { try { int strategy; try { strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks()); switch (strategy) { case SelectStrategy.CONTINUE: continue; case SelectStrategy.BUSY_WAIT: // fall-through to SELECT since the busy-wait is not supported with NIO case SelectStrategy.SELECT: long curDeadlineNanos = nextScheduledTaskDeadlineNanos(); if (curDeadlineNanos == -1L) { curDeadlineNanos = NONE; // nothing on the calendar } nextWakeupNanos.set(curDeadlineNanos); try { if (!hasTasks()) { strategy = select(curDeadlineNanos); } } finally { // This update is just to help block unnecessary selector wakeups // so use of lazySet is ok (no race condition) nextWakeupNanos.lazySet(AWAKE); } // 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(); selectCnt = 0; handleLoopException(e); continue; } selectCnt++; cancelledKeys = 0; needsToSelectAgain = false; final int ioRatio = this.ioRatio; boolean ranTasks; if (ioRatio == 100) { try { if (strategy > 0) { processSelectedKeys(); } } finally { // Ensure we always run tasks. ranTasks = runAllTasks(); } } else if (strategy > 0) { final long ioStartTime = System.nanoTime(); try { processSelectedKeys(); } finally { // Ensure we always run tasks. final long ioTime = System.nanoTime() - ioStartTime; ranTasks = runAllTasks(ioTime * (100 - ioRatio) / ioRatio); } } else { ranTasks = runAllTasks(0); // This will run the minimum number of tasks } if (ranTasks || strategy > 0) { if (selectCnt > MIN_PREMATURE_SELECTOR_RETURNS && logger.isDebugEnabled()) { logger.debug("Selector.select() returned prematurely {} times in a row for Selector {}.", selectCnt - 1, selector); } selectCnt = 0; } else if (unexpectedSelectorWakeup(selectCnt)) { // Unexpected wakeup (unusual case) selectCnt = 0; } } catch (CancelledKeyException e) { // Harmless exception - log anyway if (logger.isDebugEnabled()) { logger.debug(CancelledKeyException.class.getSimpleName() + " raised by a Selector {} - JDK bug?", selector, e); } } catch (Error e) { throw e; } catch (Throwable t) { handleLoopException(t); } finally { // Always handle shutdown even if the loop processing threw an exception. try { if (isShuttingDown()) { closeAll(); if (confirmShutdown()) { return; } } } catch (Error e) { throw e; } catch (Throwable t) { handleLoopException(t); } } } } -
runAllTasks方法
protected boolean runAllTasks(long timeoutNanos) { fetchFromScheduledTaskQueue(); Runnable task = pollTask(); if (task == null) { afterRunningAllTasks(); return false; } final long deadline = timeoutNanos > 0 ? ScheduledFutureTask.nanoTime() + timeoutNanos : 0; long runTasks = 0; long lastExecutionTime; for (;;) { safeExecute(task); runTasks ++; // Check timeout every 64 tasks because nanoTime() is relatively expensive. // XXX: Hard-coded value - will make it configurable if it is really a problem. if ((runTasks & 0x3F) == 0) { lastExecutionTime = ScheduledFutureTask.nanoTime(); if (lastExecutionTime >= deadline) { break; } } task = pollTask(); if (task == null) { lastExecutionTime = ScheduledFutureTask.nanoTime(); break; } } afterRunningAllTasks(); this.lastExecutionTime = lastExecutionTime; return true; } -
register0方法
private void register0(ChannelPromise promise) { try { // check if the channel is still open as it could be closed in the mean time when the register // call was outside of the eventLoop if (!promise.setUncancellable() || !ensureOpen(promise)) { return; } boolean firstRegistration = neverRegistered; doRegister(); neverRegistered = false; registered = true; // Ensure we call handlerAdded(...) before we actually notify the promise. This is needed as the // user may already fire events through the pipeline in the ChannelFutureListener. pipeline.invokeHandlerAddedIfNeeded(); safeSetSuccess(promise); pipeline.fireChannelRegistered(); // Only fire a channelActive if the channel has never been registered. This prevents firing // multiple channel actives if the channel is deregistered and re-registered. if (isActive()) { if (firstRegistration) { pipeline.fireChannelActive(); } else if (config().isAutoRead()) { // This channel was registered before and autoRead() is set. This means we need to begin read // again so that we process inbound data. // // See https://github.com/netty/netty/issues/4805 beginRead(); } } } catch (Throwable t) { // Close the channel directly to avoid FD leak. closeForcibly(); closeFuture.setClosed(); safeSetFailure(promise, t); } } -
doRegister()方法
@Override protected void doRegister() throws Exception { boolean selected = false; for (;;) { try { selectionKey = javaChannel().register(eventLoop().unwrappedSelector(), 0, this); return; } 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. eventLoop().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; } } } -
invokeHandlerIfNeeded方法，就是initChannel方法
p.addLast(new ChannelInitializer
() { @Override public void initChannel(final Channel ch) { final ChannelPipeline pipeline = ch.pipeline(); ChannelHandler handler = config.handler(); if (handler != null) { pipeline.addLast(handler); } ch.eventLoop().execute(new Runnable() { @Override public void run() { pipeline.addLast(new ServerBootstrapAcceptor( ch, currentChildGroup, currentChildHandler, currentChildOptions, currentChildAttrs)); } }); } });
BossGroup主要负责监听，WorkerGroup负责消息处理。
入站就是BossGroup如何将通道交给WorkerGroup以及如何进行消息处理。
BossGroup/WorkerGroup源码分析 主要源码流程-
processSelectedKeysOptimized
private void processSelectedKeysOptimized() { 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; final Object a = k.attachment(); if (a instanceof AbstractNioChannel) { processSelectedKey(k, (AbstractNioChannel) a); } else { @SuppressWarnings("unchecked") NioTasktask = (NioTask ) a; processSelectedKey(k, task); } 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; } } } -
processSelectedKey
private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) { final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe(); if (!k.isValid()) { final EventLoop eventLoop; try { eventLoop = ch.eventLoop(); } catch (Throwable ignored) { // If the channel implementation throws an exception because there is no event loop, we ignore this // because we are only trying to determine if ch is registered to this event loop and thus has authority // to close ch. return; } // Only close ch if ch is still registered to this EventLoop. ch could have deregistered from the event loop // and thus the SelectionKey could be cancelled as part of the deregistration process, but the channel is // still healthy and should not be closed. // See https://github.com/netty/netty/issues/5125 if (eventLoop == this) { // close the channel if the key is not valid anymore unsafe.close(unsafe.voidPromise()); } return; } try { int readyOps = k.readyOps(); // We first need to call finishConnect() before try to trigger a read(...) or write(...) as otherwise // the NIO JDK channel implementation may throw a NotYetConnectedException. if ((readyOps & SelectionKey.OP_CONNECT) != 0) { // remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking // See https://github.com/netty/netty/issues/924 int ops = k.interestOps(); ops &= ~SelectionKey.OP_CONNECT; k.interestOps(ops); unsafe.finishConnect(); } // Process OP_WRITE first as we may be able to write some queued buffers and so free memory. if ((readyOps & SelectionKey.OP_WRITE) != 0) { // Call forceFlush which will also take care of clear the OP_WRITE once there is nothing left to write ch.unsafe().forceFlush(); } // Also check for readOps of 0 to workaround possible JDK bug which may otherwise lead // to a spin loop if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) { unsafe.read(); } } catch (CancelledKeyException ignored) { unsafe.close(unsafe.voidPromise()); } } -
Unsafe.read()
@Override public void read() { assert eventLoop().inEventLoop(); final ChannelConfig config = config(); final ChannelPipeline pipeline = pipeline(); final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle(); allocHandle.reset(config); boolean closed = false; Throwable exception = null; try { try { do { int localRead = doReadMessages(readBuf); if (localRead == 0) { break; } if (localRead < 0) { closed = true; break; } allocHandle.incMessagesRead(localRead); } while (continueReading(allocHandle)); } catch (Throwable t) { exception = t; } int size = readBuf.size(); for (int i = 0; i < size; i ++) { readPending = false; pipeline.fireChannelRead(readBuf.get(i)); } readBuf.clear(); allocHandle.readComplete(); pipeline.fireChannelReadComplete(); if (exception != null) { closed = closeOnReadError(exception); pipeline.fireExceptionCaught(exception); } if (closed) { inputShutdown = true; if (isOpen()) { close(voidPromise()); } } } finally { // Check if there is a readPending which was not processed yet. // This could be for two reasons: // * The user called Channel.read() or ChannelHandlerContext.read() in channelRead(...) method // * The user called Channel.read() or ChannelHandlerContext.read() in channelReadComplete(...) method // // See https://github.com/netty/netty/issues/2254 if (!readPending && !config.isAutoRead()) { removeReadOp(); } } }
private void write(Object msg, boolean flush, ChannelPromise promise) {
ObjectUtil.checkNotNull(msg, "msg");
try {
if (isNotValidPromise(promise, true)) {
ReferenceCountUtil.release(msg);
// cancelled
return;
}
} catch (RuntimeException e) {
ReferenceCountUtil.release(msg);
throw e;
}
final AbstractChannelHandlerContext next = findContextOutbound(flush ?
(MASK_WRITE | MASK_FLUSH) : MASK_WRITE);
final Object m = pipeline.touch(msg, next);
EventExecutor executor = next.executor();
if (executor.inEventLoop()) {
if (flush) {
next.invokeWriteAndFlush(m, promise);
} else {
next.invokeWrite(m, promise);
}
} else {
final WriteTask task = WriteTask.newInstance(next, m, promise, flush);
if (!safeExecute(executor, task, promise, m, !flush)) {
// We failed to submit the WriteTask. We need to cancel it so we decrement the pending bytes
// and put it back in the Recycler for re-use later.
//
// See https://github.com/netty/netty/issues/8343.
task.cancel();
}
}
}
