consumer的DubboClientHandler线程池

1. 创建线程池

创建线程池的调用栈如下：

SimpleDataStore把线程池存放在map中。

public class NettyClient extends AbstractClient {
   public NettyClient(final URL url, final ChannelHandler handler) throws RemotingException{
        //首先调用父类的wrapChannelHandler方法，创建DubboClientHandler线程池
        super(url, wrapChannelHandler(url, handler));
   }
}

public abstract class AbstractClient extends AbstractEndpoint implements Client {
    protected static final String CLIENT_THREAD_POOL_NAME = "DubboClientHandler";
    //DubboClientHandler线程池
    protected volatile ExecutorService executor;
    public AbstractClient(URL url, ChannelHandler handler) throws RemotingException {
        //省略其他非相关代码
        //从SimpleDataStore中获取线程池
        executor = (ExecutorService) ExtensionLoader.getExtensionLoader(DataStore.class)
            .getDefaultExtension().get(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
        ExtensionLoader.getExtensionLoader(DataStore.class)
            .getDefaultExtension().remove(Constants.CONSUMER_SIDE, Integer.toString(url.getPort()));
    }

    protected static ChannelHandler wrapChannelHandler(URL url, ChannelHandler handler){
        //给线程命名
        url = ExecutorUtil.setThreadName(url, CLIENT_THREAD_POOL_NAME);
        url = url.addParameterIfAbsent(Constants.THREADPOOL_KEY, Constants.DEFAULT_CLIENT_THREADPOOL);
        return ChannelHandlers.wrap(handler, url);
    }
}

public class WrappedChannelHandler implements ChannelHandlerDelegate {
    protected final ExecutorService executor;
    public WrappedChannelHandler(ChannelHandler handler, URL url) {
        this.handler = handler;
        this.url = url;
        //此处创建了线程池
        executor = (ExecutorService) ExtensionLoader.getExtensionLoader(ThreadPool.class)
　　　　　　　　　　　.getAdaptiveExtension().getExecutor(url);
        String componentKey = Constants.EXECUTOR_SERVICE_COMPONENT_KEY;
        if (Constants.CONSUMER_SIDE.equalsIgnoreCase(url.getParameter(Constants.SIDE_KEY))) {
            componentKey = Constants.CONSUMER_SIDE;
        }
        DataStore dataStore = ExtensionLoader.getExtensionLoader(DataStore.class).getDefaultExtension();
        dataStore.put(componentKey, Integer.toString(url.getPort()), executor);
    }
}

executor = (ExecutorService) ExtensionLoader.getExtensionLoader(ThreadPool.class).getAdaptiveExtension().getExecutor(url);

ThreadPool$Adpative代码如下：

package com.alibaba.dubbo.common.threadpool;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
public class ThreadPool$Adpative implements com.alibaba.dubbo.common.threadpool.ThreadPool {
    public java.util.concurrent.Executor getExecutor(
            com.alibaba.dubbo.common.URL arg0) {
        if (arg0 == null)
            throw new IllegalArgumentException("url == null");
        com.alibaba.dubbo.common.URL url = arg0;
        // url中的默认参数threadpool=cached
        String extName = url.getParameter("threadpool", "fixed");
        if (extName == null)
            throw new IllegalStateException(
                    "Fail to get extension(com.alibaba.dubbo.common.threadpool.ThreadPool) name from url("
                            + url.toString() + ") use keys([threadpool])");
        com.alibaba.dubbo.common.threadpool.ThreadPool extension =
　　　　　　　　　 (com.alibaba.dubbo.common.threadpool.ThreadPool) ExtensionLoader
                .getExtensionLoader(com.alibaba.dubbo.common.threadpool.ThreadPool.class)
                .getExtension(extName);
        return extension.getExecutor(arg0);
    }
}

CachedThreadPool类：

/**
 * 此线程池可伸缩，线程空闲一分钟后回收，新请求重新创建线程
 *
 */
public class CachedThreadPool implements ThreadPool {
    public Executor getExecutor(URL url) {
        String name = url.getParameter(Constants.THREAD_NAME_KEY, Constants.DEFAULT_THREAD_NAME);
        int cores = url.getParameter(Constants.CORE_THREADS_KEY, Constants.DEFAULT_CORE_THREADS);
        int threads = url.getParameter(Constants.THREADS_KEY, Integer.MAX_VALUE);
        int queues = url.getParameter(Constants.QUEUES_KEY, Constants.DEFAULT_QUEUES);
        int alive = url.getParameter(Constants.ALIVE_KEY, Constants.DEFAULT_ALIVE);
        return new ThreadPoolExecutor(cores, threads, alive, TimeUnit.MILLISECONDS,
                queues == 0 ? new SynchronousQueue<Runnable>() :
                    (queues < 0 ? new LinkedBlockingQueue<Runnable>()
                            : new LinkedBlockingQueue<Runnable>(queues)),
                new NamedThreadFactory(name, true), new AbortPolicyWithReport(name, url));
    }
}

2. 往线程池投送任务

线程池创建之后，是谁在什么时候往里面扔任务呢？

public class AllChannelHandler extends WrappedChannelHandler {
    public void received(Channel channel, Object message) throws RemotingException {
        ExecutorService cexecutor = getExecutorService();
        try {
            //往线程池扔任务
            cexecutor.execute(new ChannelEventRunnable(channel, handler, ChannelState.RECEIVED, message));
        } catch (Throwable t) {
            throw new ExecutionException(message, channel, getClass() + " error when process received event .", t);
        }
    }
    private ExecutorService getExecutorService() {
        //executor在父类WrappedChannelHandler中
        ExecutorService cexecutor = executor;
        if (cexecutor == null || cexecutor.isShutdown()) {
            cexecutor = SHARED_EXECUTOR;
        }
        return cexecutor;
    }
}

也就是说nio线程往DubboClientHandler线程池扔任务，DubboClientHandler线程再唤醒等待的consumer调用线程。

3. 线程池执行任务