github上的esl-client已经N年未更新了，上面有一堆bug，记录一下：
一、内存泄露
org.freeswitch.esl.client.transport.message.EslFrameDecoder 这个类，使用了netty的ByteBuf，对netty有了解的同学应该知道，netty底层大量使用了堆外内存，建议开发人员及时手动释放。
https://github.com/esl-client/esl-client/issues/24 也有记载
参考下图，手动加上释放处理即可
二、线程池优化
org.freeswitch.esl.client.outbound.OutboundChannelInitializer 这个类，每次freeswitch有来电时，会以outbound外联模式，通过tcp连接到esl client，初始化channel。callbackExector是一个单线程池，正常情况下问题倒不大，但是jdk源码：
public static ExecutorService newSingleThreadExecutor() {
return new FinalizableDelegatedExecutorService
(new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>()));
}LinkedBlockingQueue默认是一个无界队列：
public LinkedBlockingQueue() {
this(Integer.MAX_VALUE);
}有点风险，改成下面这样更安全点：
private ThreadFactory namedThreadFactory = new ThreadFactoryBuilder()
.setNameFormat("outbound-pool-%d").build();
public ExecutorService callbackExecutor = new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<>(10000), namedThreadFactory);
这个单线程池的用法也顺带研究了下，它真正使用的地方在于org.freeswitch.esl.client.outbound.OutboundClientHandler，用于处理freeswitch发过来的事件
@Override
protected void handleEslEvent(final ChannelHandlerContext ctx, final EslEvent event) {
callbackExecutor.execute(() -> clientHandler.onEslEvent(
new Context(ctx.channel(), OutboundClientHandler.this), event));
}
大家知道Netty本身就有2个线程池：bossGroup，workerGroup，默认大小在io.netty.channel.MultithreadEventLoopGroup中
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);
}
}即：核数*2。 既然已经是线程池了，为啥这里esl的事件又单独交给1个单线程池来处理呢？ 先来看OutboundChannelInitializer实例化的地方，在org.freeswitch.esl.client.outbound.SocketClient的doStart里
@Override
protected void doStart() {
final ServerBootstrap bootstrap = new ServerBootstrap()
.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childOption(ChannelOption.TCP_NODELAY, true)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childHandler(new OutboundChannelInitializer(clientHandlerFactory));
serverChannel = bootstrap.bind(bindAddress).syncUninterruptibly().channel();
notifyStarted();
log.info("SocketClient waiting for connections on [{}] ...", bindAddress);
}
也就是说，只有outbound tcp server启用时，才会对OutboundChannelInitializer做1次初始化，言外之意，刚才的单线程池实例也只会实例化1次。
试想一下，如果在outbound的处理过程中，一通电话进来，我们订阅了一堆事件，这堆事件发过来后，如果让workerGroup并行处理，事件的处理顺序就得不到保证了，这在电话系统中是很重要的，比如：响铃->接听->挂断。肯定要有顺序的！所以为了保证事件处理的顺序性，强制让所有事件，都交给这个单线程池实例来处理，保证了顺序性。
其实不光是outbound，inbound也是类似机制，保证事件接收时按顺序处理。明白这个原理后，回过头来想想，这个单线程池的callbackExector实例，应该处理成static静态实例更稳妥，这样强制让jvm保证肯定只有一个实例，处理事件绝对有顺序。
另外，在outbound的onConnect事件里，如果尝试跟freeswitch发命令，会发现block住，后面的代码完全无法执行，这也是一个大坑。解决办法：
将onConnect的处理，放在另外1个专用线程池里
class OutboundClientHandler extends AbstractEslClientHandler {
//这是保证事件接收顺序的单线程池
private final ExecutorService onEslEventExecutor;
//这是用于并发处理onConnect的多线程池
private final ExecutorService onConnectExecutor;
public OutboundClientHandler(IClientHandler clientHandler, ExecutorService onEslEventExecutor, ExecutorService onConnectExecutor) {
this.clientHandler = clientHandler;
//构造函数里允许传入
this.onEslEventExecutor = onEslEventExecutor;
this.onConnectExecutor = onConnectExecutor;
}
@Override
public void channelActive(final ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
// Have received a connection from FreeSWITCH server, send connect response
long threadId = Thread.currentThread().getId();
log.debug("Received new connection from server, sending connect message,threadId:" + threadId);
sendApiSingleLineCommand(ctx.channel(), "connect")
.thenAccept(response ->
//这里改为线程池执行
onConnectExecutor.execute(() -> clientHandler.onConnect(
new Context(ctx.channel(), OutboundClientHandler.this),
new EslEvent(response, true)))
)
.exceptionally(throwable -> {
ctx.channel().close();
handleDisconnectionNotice();
return null;
});
}
@Override
protected void handleEslEvent(final ChannelHandlerContext ctx, final EslEvent event) {
//这里仍然用单一线程池处理，保证顺序
onEslEventExecutor.execute(() -> clientHandler.onEslEvent(
new Context(ctx.channel(), OutboundClientHandler.this), event));
}
...
}然后
public class OutboundChannelInitializer extends ChannelInitializer<SocketChannel> {
private final IClientHandlerFactory clientHandlerFactory;
private static ThreadFactory onEslThreadFactory = new ThreadFactoryBuilder()
.setNameFormat("outbound-onEsl-pool-%d").build();
//专门接收订阅事件的单一线程池(保证顺序)
private static ExecutorService onEslExecutor = new ThreadPoolExecutor(1, 1,
0L, TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<>(100000), onEslThreadFactory);
private static ThreadFactory onConnectThreadFactory = new ThreadFactoryBuilder()
.setNameFormat("outbound-onConnect-pool-%d").build();
//专用于处理新来电onConnect的多线程池
private static ExecutorService onConnectExecutor = new ThreadPoolExecutor(32, 512,
60L, TimeUnit.SECONDS,
new LinkedBlockingQueue<>(2048), onConnectThreadFactory);
public OutboundChannelInitializer(IClientHandlerFactory clientHandlerFactory) {
this.clientHandlerFactory = clientHandlerFactory;
}
/**
* 重载版本，允许开发人员初始化时，传入自己的线程池
* @param clientHandlerFactory
* @param connExecutor
* @param eslExecutor
*/
public OutboundChannelInitializer(IClientHandlerFactory clientHandlerFactory, ExecutorService connExecutor, ExecutorService eslExecutor) {
this.clientHandlerFactory = clientHandlerFactory;
onEslExecutor = eslExecutor;
onConnectExecutor = connExecutor;
}
@Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// Add the text line codec combination first
pipeline.addLast("encoder", new StringEncoder());
// Note that outbound mode requires the decoder to treat many 'headers' as body lines
pipeline.addLast("decoder", new EslFrameDecoder(8092, true));
// now the outbound client logic
//将2个线程池，传入实例
pipeline.addLast("clientHandler",
new OutboundClientHandler(clientHandlerFactory.createClientHandler(), onEslExecutor, onConnectExecutor));
}
}
三、源码上的Test示例代码各种错误
https://github.com/esl-client/esl-client/blob/master/src/test/java/OutboundTest.java 这是示例源码
String uuid = eslEvent.getEventHeaders().get("unique-id");45行，这里应该是"Unique-ID"，小写取不到值。
另外82行，outbound的onEslEvent方法，其实永远也不会被触发，因为根本没订阅任何事件，inbound的示例部分也有同样问题。
56行，执行后，实测下来，后面的操作其实都是阻塞的，代码无法向下执行，建议改在新线程里执行(或者参考上面的“线程池优化”分析，修改源码)。
上述这些问题，笔者已经fork了一份代码进行了修改，有兴趣的同学，欢迎fork，地址：https://github.com/yjmyzz/esl-client
作者：菩提树下的杨过
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