Selector监听的事件
NIO事件/感兴趣事件
OP_REGISTER = 0 通道注册事件
OP_READ = 1 << 0
OP_WRITE = 1 << 2
OP_CONNECT = 1 << 3
OP_ACCEPT = 1 << 4
执行流程
1、客户端与服务器建立连接， BossGroupNioEventLoop 监听到有IO事件，那么处理选择的key ----processSelectedKeys（）
/**
* NIOEventLoop执行核心
*/
@Override
protected void run() {
int selectCnt = 0; // 阻塞选择次数
// 从NioEventLoop中的 taskQueue中 判断是否存在事件
for (;;) { // 轮训注册到selector的IO事件 为什么for(;;)比while(1)好？因为for(;;)底层的指令更少，效率更高
try {
int strategy; // strategy = 0 default
try {
strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks()); // 获取策略。如果有任务则使用非阻塞方式
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: // select事件执行
long curDeadlineNanos = nextScheduledTaskDeadlineNanos(); // 当前截止时间
if (curDeadlineNanos == -1L) { // 表明没有定时任务
curDeadlineNanos = NONE; // nothing on the calendar
}
nextWakeupNanos.set(curDeadlineNanos);
try {
if (!hasTasks()) { // 如果没有任务，则select阻塞等待任务 任务存放在SingleThreadEventLoop
// TODO 测试
System.err.println("[CurrentThread = " + Thread.currentThread().getName() + "]I'm selecting... waiting for selectKey or tasks!");
strategy = select(curDeadlineNanos);
}
} finally {
// This update is just to help block unnecessary selector wakeups
// so use of lazySet is ok (no race condition)
// 标记未唤醒状态
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;
}
System.err.println("[CurrentThread = " + Thread.currentThread().getName() + "] select() 调用完了，此时已经有事件进来了？");
selectCnt++; // 选择次数+1
cancelledKeys = 0;
needsToSelectAgain = false;
final int ioRatio = this.ioRatio; // 这里的ioRatio默认是50
boolean ranTasks;
if (ioRatio == 100) {
try {
if (strategy > 0) {
processSelectedKeys(); // 处理选择key，处理io相关的逻辑
}
} finally {
ranTasks = runAllTasks(); // 处理外部线程扔到taskQueue里的任务，这里的taskQueue是一个mpscQueue
}
} else if (strategy > 0) {
final long ioStartTime = System.nanoTime(); // 计算处理选择key的时间
try {
processSelectedKeys();
} finally {
// Ensure we always run tasks.
final long ioTime = System.nanoTime() - ioStartTime;
ranTasks = runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
}
} else {
/**
* 在Netty中，有两种任务，普通任务和定时任务。在执行任务的时候，会把定时任务队列里的task扔进普通任务队列里，
* 这里的普通任务队列就是mpscQueue，接着就挨个执行mpscQueue里的任务。
*
* 任务：普通任务 、定时任务
* 队列：普通任务队列mpscQueue 、 定时任务队列
*
*/
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) 解决空轮训Bug，重置selectCnt，重新生成selector
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 (Error) 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 (Error) e;
} catch (Throwable t) {
handleLoopException(t);
}
}
}
}2、获取到当前NioEventLoop中 通道（ServerSocketChannel）注册到selector 产生的所有令牌 SelectionKeySet，获取到ServerSocketChannel，来处理这个IO事件（建立连接事件）
* 优化过后处理SelectedKey方法
*/
private void processSelectedKeysOptimized() {
// 迭代selectedKey数组
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/236
// 这种感兴趣的事件只处理一次就行
selectedKeys.keys[i] = null;
// 获取注册到NioEventLoop里的channel
// 获取出 attachment,默认情况下就是注册进Selector时,传入的第三个参数 this===> NioServerSocketChannel
// 一个Selector中可能被绑定上了成千上万个Channel, 通过K+attachment 的手段, 精确的取出发生指定事件的channel, 进而获取channel中的unsafe类进行下一步处理
final Object a = k.attachment();
if (a instanceof AbstractNioChannel) {
// 这里为啥要将NioServerSocketChannel强转为AbstractNioChannel呢？
// 这里强转为AbstractNioChannel是为了准备调用jdk channel的accept方法
processSelectedKey(k, (AbstractNioChannel) a);
} else {
@SuppressWarnings("unchecked")
NioTask<SelectableChannel> task = (NioTask<SelectableChannel>) a;
processSelectedKey(k, task);
}
// 疑问：什么情况下这里会出现true的情况，需要重新select？
// 答：每当256个channel从Selector上移除时，就标记needsToSelectAgain为true，表示需要再次轮询
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;
}
}
}private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe(); // 获取channel内部的unsafe方法
if (!k.isValid()) { // 如果key不合法
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
// 关闭通道，如果key是非法的
unsafe.close(unsafe.voidPromise());
}
return;
}
try {
int readyOps = k.readyOps(); // 获取感兴趣的IO事件
// 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) { // 如果当前感兴趣事件不是连接事件
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
/**
* 将ops事件设置成OP_CONNECT事件
* 另外一种写法为：
*
* k.interestOps(readyOps & ~SelectionKey.OP_CONNECT)
* OP_CONNECT是8，即1000，取反则为：111，如果k是0，则 000 & 111 = 000
*
*/
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
// readyOps = 0 表示的是channel注册事件
// 如果是workerGroup，可能是OP_READ的IO事件，如果是bossGroup，可能是OP_ACCEPT的IO事件
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
// 负责读，接受连接事件
unsafe.read();
}
} catch (CancelledKeyException ignored) {
unsafe.close(unsafe.voidPromise());
}
}
感兴趣事件 16
1、获取通道 NioMessageUnsafe 主要负责服务端读写数据的 非常重要
2、判断ServerSocketChannel是否合法，不合法关闭
3、获取 channel 注册到 Selector 指定监听的事件，这里是 ON_ACCEPT 建立连接事件
4、调用NioMessageUnsafe 处理事件
/**
* read()方法的核心三个步骤：
* 1. doReadMessages(readBuf)
* 2. allocHandle.incMessagesRead(localRead)
* 3. pipeline.fireChannelRead(readBuf.get(i))
*
*/
@Override
public void read() {
assert eventLoop().inEventLoop();
final ChannelConfig config = config(); // 服务端的Config
final ChannelPipeline pipeline = pipeline(); // pipleline管道
final RecvByteBufAllocator.Handle allocHandle = unsafe().recvBufAllocHandle(); // 用于查看服务端接受的速率, 说白了就是控制服务端是否接着read 客户端的IO事件
allocHandle.reset(config); // 重置配置
boolean closed = false;
Throwable exception = null;
try {
try {
do {
// 往readBuf 添加客户端socketChannel
int localRead = doReadMessages(readBuf);
if (localRead == 0) {
break;
}
if (localRead < 0) {
closed = true;
break;
}
// 简单的计数
allocHandle.incMessagesRead(localRead);
} while (allocHandle.continueReading());
} catch (Throwable t) {
exception = t;
}
int size = readBuf.size();
for (int i = 0; i < size; i ++) {
readPending = false;
// 处理新的连接之后，让pipeline中发生事件传播
// 这里的pipeline是服务端的
// 事件是如何传播的？head --> ServerBootStrapAcceptor --> tail 依次传播
// 这里传播的什么事件? ChannelRead, 也就是说,会去调用 ServerBootStraptAcceptor的ChannelRead方法
// readBuf.get(i)这里获取到的是NioSocketChannel对象
// TODO 是这里把新的NioSocketChannel注册进workerGroup里的，需要注意的是workerGroup注册完之后，只有16个NioEventLoop，但是
// TODO 没有NioSocketChannel
pipeline.fireChannelRead(readBuf.get(i)); // 链式调用channelRead
}
readBuf.clear();
allocHandle.readComplete();
// 传播channelReadComplete事件
pipeline.fireChannelReadComplete(); // 链式调用ChannelReadComplete
if (exception != null) {
closed = closeOnReadError(exception);
// 传播exceptionCaught事件
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();
}
}
}
}1、NioEventLoop Selector监听到有连接事件，调用ServerSocketChannel accpt方法接收封装成NioSocketChannel到list中，这不会堵塞当前线程，没有客户端建立连接直接返回null，普通的accept方法会堵塞当前线程。
2、获取ServerSocketChannel的pipeline，通过 ServerBootstrapAcceptor （ChannelHandler）将客户端SocketChannel 注册到workerGroup中
客户端SocketChannel 注册流程 跟 ServerSocketChannel一致，这里就不赘述了
ServerBootstrapAcceptor 负责将客户端SocketChannel 交由 workGroup线程组处理
childGroup 就是 WorkerGroup，内部会遍历选出一个WorkerNioEventLoop，获取其中的Selector ，将当前客户端SocketChannel绑定上去，并监听 read/write 事件
后续客户端SocketChannel 数据通信 交由服务器端WorkerNioEevntLoop进行数据处理
3、WorkerNioEevntLoop读取SocketChannel 数据
Selector 监听到 通道有IO事件，处理选择的key
private void processSelectedKey(SelectionKey k, AbstractNioChannel ch) {
final AbstractNioChannel.NioUnsafe unsafe = ch.unsafe(); // 获取channel内部的unsafe方法
if (!k.isValid()) { // 如果key不合法
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
// 关闭通道，如果key是非法的
unsafe.close(unsafe.voidPromise());
}
return;
}
try {
int readyOps = k.readyOps(); // 获取感兴趣的IO事件
// 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) { // 如果当前感兴趣事件不是连接事件
// remove OP_CONNECT as otherwise Selector.select(..) will always return without blocking
// See https://github.com/netty/netty/issues/924
int ops = k.interestOps();
/**
* 将ops事件设置成OP_CONNECT事件
* 另外一种写法为：
*
* k.interestOps(readyOps & ~SelectionKey.OP_CONNECT)
* OP_CONNECT是8，即1000，取反则为：111，如果k是0，则 000 & 111 = 000
*
*/
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
// readyOps = 0 表示的是channel注册事件
// 如果是workerGroup，可能是OP_READ的IO事件，如果是bossGroup，可能是OP_ACCEPT的IO事件
if ((readyOps & (SelectionKey.OP_READ | SelectionKey.OP_ACCEPT)) != 0 || readyOps == 0) {
// 负责读，接受连接事件
unsafe.read();
}
} catch (CancelledKeyException ignored) {
unsafe.close(unsafe.voidPromise());
}
}SelectionKey 中存储的感兴趣的事件 1 ，及读取数据事件，通知WorkerNioSocketChannel中的NioSocketChannelUnsafe读取数据。
NioSocketChannelUnsafe主要负责读取客户端的数据，想客户端写数据。
ServerSocketChannel数据读写类是NioMessageUnsafe 注意这两个不一样哦！！！
/**
* 客户端channel的读，读取的是数据
* 如果数据量大，数据会分为多次读，最多为16次
*/
@Override
public final void read() {
final ChannelConfig config = config();
if (shouldBreakReadReady(config)) {
clearReadPending();
return;
}
final ChannelPipeline pipeline = pipeline();
final ByteBufAllocator allocator = config.getAllocator();
// 自适应数据大小的分配器，在io.netty.channel.DefaultChannelConfig中设置的RecvByteBufAllocator，默认是AdaptiveRecvByteBufAllocator
final RecvByteBufAllocator.Handle allocHandle = recvBufAllocHandle();
allocHandle.reset(config);
ByteBuf byteBuf = null;
boolean close = false;
try {
do {
byteBuf = allocHandle.allocate(allocator); // 尽可能分配合适的大小: guess()方法很形象，猜下系统分配了多少？
allocHandle.lastBytesRead(doReadBytes(byteBuf)); // 读并且记录读了多少，如果读满了，下次continue的话就直接扩容
if (allocHandle.lastBytesRead() <= 0) {
// nothing was read. release the buffer.
byteBuf.release();
byteBuf = null;
close = allocHandle.lastBytesRead() < 0;
if (close) {
// There is nothing left to read as we received an EOF.
readPending = false;
}
break;
}
allocHandle.incMessagesRead(1); // 表示读了一次
readPending = false;
/**
* 触发pipeline中的chanelRead，把读取到的数据传播出去
*/
pipeline.fireChannelRead(byteBuf);
byteBuf = null;
} while (allocHandle.continueReading());
allocHandle.readComplete(); // 记录这次读事件总共读了多少数据，计算下次分配大小
pipeline.fireChannelReadComplete(); // 相当于完成本次读事件的处理
if (close) {
closeOnRead(pipeline);
}
} catch (Throwable t) {
handleReadException(pipeline, byteBuf, t, close, allocHandle);
} 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();
}
}
}
}1、 allocHandle.allocate(allocator); 拿到分配处理器，获取一个大小为2048 的 byteBuf 来存放客户端发送来的数据
内存缓存区分配器netty具体实现有两种：
- 堆内字节缓冲分配器
- 堆外字节缓冲分配器
默认使用的好像是堆外内存
那么堆内堆外内存区别在哪？？？，先留着
2、记录读取的数据量，方便扩容
3、记录数据读取次数
4、调用workerNioEventLoop的 pipeLine 链式调用 channelRead
这里会走到我们定义的ChannelHandler ChannelRead 方法哦
这里会通过while判断是否继续读，没读完继续读，最多读16次
5、链式调用 ChannelReadComplete()
表示客户端的数据读完了
4、WorkerNioEevntLoop 向 SocketChannel 写数据
我们通过ChannelHandlerContext 来向通道写数据
Unpooled.copiedBuffer("叫我靓仔！！！".getBytes()) 数据转字节数组，通过Unpooled封装成 堆内缓冲区 heapByteBuf
写数据本质上就是获取到当前NioSocketChannelUnsafe 往通道写数据
/**
* 向客户端socket最终写的方法，底层调用的是JDK底层的IOUtil#write
* @param in
* @throws Exception
*/
@Override
protected void doWrite(ChannelOutboundBuffer in) throws Exception {
// jdk channel
SocketChannel ch = javaChannel();
// 写自旋次数，默认为16次
int writeSpinCount = config().getWriteSpinCount();
do {
if (in.isEmpty()) {
// All written so clear OP_WRITE
clearOpWrite();
// Directly return here so incompleteWrite(...) is not called.
return;
}
// Ensure the pending writes are made of ByteBufs only.
int maxBytesPerGatheringWrite = ((NioSocketChannelConfig) config).getMaxBytesPerGatheringWrite();
/**
* 将ChannelOutboundBuffer中的ByteBuf转为ByteBuffer数组
*/
ByteBuffer[] nioBuffers = in.nioBuffers(1024, maxBytesPerGatheringWrite);
int nioBufferCnt = in.nioBufferCount();
// Always use nioBuffers() to workaround data-corruption.
// See https://github.com/netty/netty/issues/2761
switch (nioBufferCnt) {
case 0:
// We have something else beside ByteBuffers to write so fallback to normal writes.
writeSpinCount -= doWrite0(in);
break;
case 1: {
// Only one ByteBuf so use non-gathering write
// Zero length buffers are not added to nioBuffers by ChannelOutboundBuffer, so there is no need
// to check if the total size of all the buffers is non-zero.
ByteBuffer buffer = nioBuffers[0];
int attemptedBytes = buffer.remaining();
/**
* 调用jdk底层channel的write
*/
final int localWrittenBytes = ch.write(buffer);
if (localWrittenBytes <= 0) {
incompleteWrite(true);
return;
}
adjustMaxBytesPerGatheringWrite(attemptedBytes, localWrittenBytes, maxBytesPerGatheringWrite);
in.removeBytes(localWrittenBytes);
--writeSpinCount;
break;
}
default: {
// Zero length buffers are not added to nioBuffers by ChannelOutboundBuffer, so there is no need
// to check if the total size of all the buffers is non-zero.
// We limit the max amount to int above so cast is safe
long attemptedBytes = in.nioBufferSize();
final long localWrittenBytes = ch.write(nioBuffers, 0, nioBufferCnt);
if (localWrittenBytes <= 0) {
incompleteWrite(true);
return;
}
// Casting to int is safe because we limit the total amount of data in the nioBuffers to int above.
adjustMaxBytesPerGatheringWrite((int) attemptedBytes, (int) localWrittenBytes,
maxBytesPerGatheringWrite);
in.removeBytes(localWrittenBytes);
--writeSpinCount;
break;
}
}
} while (writeSpinCount > 0);
incompleteWrite(writeSpinCount < 0);
}写完后将数据刷新出去就行了
问题
1、workerGroup如果定义了16个NioEvetLoop ，在创建NioEvetLoop中会直接创建线程执行嘛？
我的理解是不会！只有当客户端与服务端建立连接的时候，ServerSocketChannel所在NioEventLoop将 接收到的SocketChannel通过 ServerBootAcceptor 交由 WorkerGroup NioEventLoop注册通道的时候，才会拿到这个WorkerNioEventLoop 创建线程，进行Selector监听。
2、netty服务端数据 怎么接收，数据存放的内存通过什么分配？怎么分配？
/**
* 内存分配管理器接口抽象，负责分配所有的内存
*
* 在Netty中可以分为两类内存缓冲分配器：1. 基于内存池的字节缓冲区分配器；2. 非内存池的字节缓冲区分配器；
*
* Implementations are responsible to allocate buffers. Implementations of this interface are expected to be
* thread-safe.
*/
public interface ByteBufAllocator {
ByteBufAllocator DEFAULT = ByteBufUtil.DEFAULT_ALLOCATOR;
/**
* 负责分配一块内存
* 具体分配一块堆内存还是堆外内存，由具体的实现类来决定
*
* Allocate a {@link ByteBuf}. If it is a direct or heap buffer
* depends on the actual implementation.
*/
ByteBuf buffer();
/**
* 分配一个初始化容量为initialCapacity的字节缓冲区
* Allocate a {@link ByteBuf} with the given initial capacity.
* If it is a direct or heap buffer depends on the actual implementation.
*/
ByteBuf buffer(int initialCapacity);
/**
* Allocate a {@link ByteBuf} with the given initial capacity and the given
* maximal capacity. If it is a direct or heap buffer depends on the actual
* implementation.
*/
ByteBuf buffer(int initialCapacity, int maxCapacity);
/**
* 分配一个DirectByteBuffer，因为DirectByteBuffer的IO操作性能更高
* Allocate a {@link ByteBuf}, preferably a direct buffer which is suitable for I/O.
*/
ByteBuf ioBuffer();
/**
* 负责分配一块指定容量initialCapacity的DirectByteBuffer区域用于IO
*
* Allocate a {@link ByteBuf}, preferably a direct buffer which is suitable for I/O.
*/
ByteBuf ioBuffer(int initialCapacity);
/**
* 负责分配一块directBuf区域用于IO
*
* Allocate a {@link ByteBuf}, preferably a direct buffer which is suitable for I/O.
*/
ByteBuf ioBuffer(int initialCapacity, int maxCapacity);
/**
* Allocate a heap {@link ByteBuf}.
*/
ByteBuf heapBuffer();
/**
* Allocate a heap {@link ByteBuf} with the given initial capacity.
*/
ByteBuf heapBuffer(int initialCapacity);
/**
* Allocate a heap {@link ByteBuf} with the given initial capacity and the given
* maximal capacity.
*/
ByteBuf heapBuffer(int initialCapacity, int maxCapacity);
/**
* Allocate a direct {@link ByteBuf}.
*/
ByteBuf directBuffer();
/**
* Allocate a direct {@link ByteBuf} with the given initial capacity.
*/
ByteBuf directBuffer(int initialCapacity);
/**
* Allocate a direct {@link ByteBuf} with the given initial capacity and the given
* maximal capacity.
*/
ByteBuf directBuffer(int initialCapacity, int maxCapacity);
/**
* 可以将heapBuf和DirectBuf合并到一个地方去使用，既CompositeByteBuf
*
* Allocate a {@link CompositeByteBuf}.
* If it is a direct or heap buffer depends on the actual implementation.
*/
CompositeByteBuf compositeBuffer();
/**
* Allocate a {@link CompositeByteBuf} with the given maximum number of components that can be stored in it.
* If it is a direct or heap buffer depends on the actual implementation.
*/
CompositeByteBuf compositeBuffer(int maxNumComponents);
/**
* Allocate a heap {@link CompositeByteBuf}.
*/
CompositeByteBuf compositeHeapBuffer();
/**
* Allocate a heap {@link CompositeByteBuf} with the given maximum number of components that can be stored in it.
*/
CompositeByteBuf compositeHeapBuffer(int maxNumComponents);
/**
* Allocate a direct {@link CompositeByteBuf}.
*/
CompositeByteBuf compositeDirectBuffer();
/**
* Allocate a direct {@link CompositeByteBuf} with the given maximum number of components that can be stored in it.
*/
CompositeByteBuf compositeDirectBuffer(int maxNumComponents);
/**
* Returns {@code true} if direct {@link ByteBuf}'s are pooled
*/
boolean isDirectBufferPooled();
/**
* Calculate the new capacity of a {@link ByteBuf} that is used when a {@link ByteBuf} needs to expand by the
* {@code minNewCapacity} with {@code maxCapacity} as upper-bound.
*/
int calculateNewCapacity(int minNewCapacity, int maxCapacity);
}总结
总体流程图(缺少一部分)
