1. 前言
Boomvc完成已经有一段时间了，但拖延到现在才开始记录。写这篇文章主要是回忆和复盘一下思路。如题所讲，Boomvc是一个mvc框架，但是它自带http server功能，也就是说不需要tomcat之类的server，可以在一个jar包里启动而不需要其他的依赖，这就需要自己去写http server的实现，这一篇我就梳理一下实现。
2. server接口
首先定义一个server接口
public interface Server {
void init(Boom boom);
void start();
void stop();
}这个接口可以有多种实现，可以从nio socket开始写，也可以用netty这样的非常好用的network层的框架实现。在这里我实现了一个简易版的TinyServer。
public class TinyServer implements Server {
private static final Logger logger = LoggerFactory.getLogger(TinyServer.class);
private Boom boom;
private Ioc ioc;
private MvcDispatcher dispatcher;
private Environment environment;
private EventExecutorGroup boss;
private EventExecutorGroup workers;
private Thread cleanSession;
@Override
public void init(Boom boom) {
...
...
}
@Override
public void start() {
this.boss.start();
this.workers.start();
this.cleanSession.start();
}
@Override
public void stop() {
this.boss.stop();
this.workers.stop();
}
}在这里要关注这个地方
private EventExecutorGroup boss;
private EventExecutorGroup workers;这是我抽象出来的表示线程组，一个EventExecuteGroup持有多个EventExecute，boss接受连接请求，workers执行业务逻辑。看一下EventExecuteGroup的实现。
public class EventExecutorGroup implements Task {
private int threadNum;
private List<EventExecutor> executorList;
private int index;
private ThreadFactory threadName;
private EventExecutorGroup childGroup;
private MvcDispatcher dispatcher;
public EventExecutorGroup(int threadNum, ThreadFactory threadName, EventExecutorGroup childGroup, MvcDispatcher dispatcher, SessionManager sessionManager) {
this.threadNum = threadNum;
this.threadName = threadName;
this.childGroup = childGroup;
this.dispatcher = dispatcher;
this.executorList = new ArrayList<>(this.threadNum);
IntStream.of(this.threadNum)
.forEach(i-> {
try {
this.executorList.add(new EventExecutor(this.threadName, this.childGroup, this.dispatcher, sessionManager));
} catch (IOException e) {
throw new RuntimeException(e);
}
});
this.index = 0;
}
public void register(SelectableChannel channel, int ops) throws ClosedChannelException {
int index1 = 0;
synchronized (this){
index1 = this.index%this.threadNum;
this.index++;
}
this.executorList.get(index1).register(channel, ops);
}
public void register(SelectableChannel channel, int ops, Object att) throws ClosedChannelException {
int index1 = 0;
synchronized (this){
index1 = this.index%this.threadNum;
this.index++;
}
this.executorList.get(index1).register(channel, ops, att);
}
@Override
public void start() {
this.executorList.forEach(e->e.start());
}
@Override
public void stop() {
this.executorList.forEach(e->e.stop());
}
}3. EventExecutor
EventExecutor就是一个io线程，它持有一个selector，selector是Java NIO核心组件中的一个，用于检查一个或多个Channel（通道）的状态是否处于可读、可写。如此可以实现单线程管理多个channels,也就是可以管理多个网络链接。io线程就不断轮询这个selector，获取多个selector key，根据这个key的状态，比如accept，read，write执行不同的逻辑。在这里EventExecutor是有多个的，也就是说selector有多个，boss EventExecutorGroup只有一个EventExecutor，它负责accept连接请求，并把接受的连接注册到workers EventExecutorGroup里，由worker线程处理read和write。
public class EventExecutor {
private static final Logger logger = LoggerFactory.getLogger(EventExecutor.class);
private ThreadFactory threadName;
private EventExecutorGroup childGroup;
private Selector selector;
private Thread ioThread;
private MvcDispatcher dispatcher;
private Runnable task;
private Semaphore semaphore = new Semaphore(1);
public EventExecutor(ThreadFactory threadName, EventExecutorGroup childGroup, MvcDispatcher dispatcher, SessionManager sessionManager) throws IOException {
this.threadName = threadName;
this.childGroup = childGroup;
this.dispatcher = dispatcher;
this.selector = Selector.open();
this.task = new EventLoop(selector, this.childGroup, this.dispatcher, sessionManager, semaphore);
this.ioThread = threadName.newThread(this.task);
}
public void register(SelectableChannel channel, int ops) throws ClosedChannelException {
channel.register(this.selector, ops);
}
public void register(SelectableChannel channel, int ops, Object att) throws ClosedChannelException {
/* 将接收的连接注册到selector上
// 发现无法直接注册，一直获取不到锁
// 这是由于 io 线程正阻塞在 select() 方法上，直接注册会造成死锁
// 如果这时直接调用 wakeup，有可能还没有注册成功又阻塞了，可以使用信号量从 select 返回后先阻塞，等注册完后在执行
*/
try {
this.semaphore.acquire();
this.selector.wakeup();
channel.register(this.selector, ops, att);
}catch (InterruptedException e){
logger.error("", e);
}finally {
this.semaphore.release();
}
}
public void start(){
((Task)this.task).start();
this.ioThread.start();
}
public void stop(){
((Task)this.task).stop();
}
}selector轮询是在EventLoop这里实现的。
3. EventLoop
public class EventLoop implements Runnable, Task {
private static final Logger logger = LoggerFactory.getLogger(EventLoop.class);
private Selector selector;
private EventExecutorGroup childGroup;
private MvcDispatcher dispatcher;
private FilterMapping filterMapping;
private volatile boolean isStart = false;
private Semaphore semaphore;
private SessionManager sessionManager;
public EventLoop(Selector selector, EventExecutorGroup childGroup, MvcDispatcher dispatcher, SessionManager sessionManager, Semaphore semaphore) {
...
}
@Override
public void run() {
while(this.isStart){
try {
int n = -1;
try {
n = selector.select(1000);
semaphore.acquire();
} catch (InterruptedException e) {
logger.error("", e);
} finally {
semaphore.release();
}
if(n<=0)
continue;
} catch (IOException e) {
logger.error("", e);
continue;
}
Iterator<SelectionKey> iterator = selector.selectedKeys().iterator();
while(iterator.hasNext()){
SelectionKey key = iterator.next();
iterator.remove();
if(!key.isValid())
continue;
try {
if (key.isAcceptable()) {
accept(key);
}
if (key.isReadable()) {
read(key);
}
if (key.isWritable()) {
write(key);
}
}catch (Exception e){
if(key!=null&&key.isValid()){
try {
key.channel().close();
} catch (IOException e1) {
e1.printStackTrace();
}
}
logger.error("", e);
}
}
}
}
private void accept(SelectionKey key) throws IOException {
ServerSocketChannel serverSocketChannel = (ServerSocketChannel) key.channel();
SocketChannel socketChannel = serverSocketChannel.accept();
socketChannel.configureBlocking(false);
this.childGroup.register(socketChannel, SelectionKey.OP_READ, new HttpProtocolParser(socketChannel));
}
private void read(SelectionKey key) throws Exception{
...
}
private void write(SelectionKey key) throws IOException {
...
}
@Override
public void start() {
this.isStart = true;
}
@Override
public void stop() {
this.filterMapping.distory();
this.isStart = false;
}
public Semaphore semaphore(){
return this.semaphore;
}
}这就是一个经典的nio程序模式，要注意这里
this.childGroup.register(socketChannel, SelectionKey.OP_READ, new HttpProtocolParser(socketChannel));这就把接受的连接注册到其他selector了。
这里我用了一个nio程序的多reactor模式，主线程中EventLoop对象通过 select监控连接建立事件，收到事件后通过 Acceptor接收，将新的连接分配给某个子EventLoop。
子线程中的EventLoop完成 read -> 业务处理 -> send 的完整流程。这种模式主线程和子线程的职责非常明确，主线程只负责接收新连接，子线程负责完成后续的业务处理，并且使用多个selector，read，业务处理，write不会影响accept，这对于大量并发连接可以提高accept的速度，不会因业务处理使大量连接堆积，这里其实参考了netty的思想。如下图
3. 遇到的坑
在写EventExecutor的register方法是，发现如果直接在selector上调用register的话，可能会造成死锁。因为selector被多个线程访问，当其中一个线程调用selector.select()方法时发生阻塞，这个线程会一直持有selector的锁，这时另一个线程的register方法会被阻塞。如果这时直接调用 wakeup，有可能还没有注册成功又阻塞了，可以使用信号量从 select 返回后先阻塞，等注册完后在执行。具体实现如下
try {
this.semaphore.acquire();
this.selector.wakeup();
channel.register(this.selector, ops, att);
}catch (InterruptedException e){
logger.error("", e);
}finally {
this.semaphore.release();
} try {
n = selector.select(1000);
semaphore.acquire();
} catch (InterruptedException e) {
logger.error("", e);
} finally {
semaphore.release();
}这里semaphore就起到一个阻塞EventLoop在被唤醒时继续执行的作用，当注册完成时才继续执行。
好了，关于server的线程部分就写到这，下一篇写http协议解析部分。
