/* * Copyright 1999-2011 Alibaba Group. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.alibaba.dubbo.rpc.cluster.support; import java.util.ArrayList; import java.util.List; import java.util.concurrent.BlockingQueue; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.LinkedBlockingQueue; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicInteger; import com.alibaba.dubbo.common.Constants; import com.alibaba.dubbo.common.utils.NamedThreadFactory; import com.alibaba.dubbo.rpc.Invocation; import com.alibaba.dubbo.rpc.Invoker; import com.alibaba.dubbo.rpc.Result; import com.alibaba.dubbo.rpc.RpcContext; import com.alibaba.dubbo.rpc.RpcException; import com.alibaba.dubbo.rpc.cluster.Directory; import com.alibaba.dubbo.rpc.cluster.LoadBalance; /** * 并行调用,只要一个成功即返回,通常用于实时性要求较高的操作,但需要浪费更多服务资源。 * * <a href="http://en.wikipedia.org/wiki/Fork_(topology)">Fork</a> * * @author william.liangf */ public class ForkingClusterInvoker<T> extends AbstractClusterInvoker<T>{ private final ExecutorService executor = Executors.newCachedThreadPool(new NamedThreadFactory("forking-cluster-timer", true)); public ForkingClusterInvoker(Directory<T> directory) { super(directory); } @SuppressWarnings({ "unchecked", "rawtypes" }) public Result doInvoke(final Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException { checkInvokers(invokers, invocation); final List<Invoker<T>> selected; final int forks = getUrl().getParameter(Constants.FORKS_KEY, Constants.DEFAULT_FORKS); final int timeout = getUrl().getParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT); if (forks <= 0 || forks >= invokers.size()) { selected = invokers; } else { selected = new ArrayList<Invoker<T>>(); for (int i = 0; i < forks; i++) { //在invoker列表(排除selected)后,如果没有选够,则存在重复循环问题.见select实现. Invoker<T> invoker = select(loadbalance, invocation, invokers, selected); if(!selected.contains(invoker)){//防止重复添加invoker selected.add(invoker); } } } RpcContext.getContext().setInvokers((List)selected); final AtomicInteger count = new AtomicInteger(); final BlockingQueue<Object> ref = new LinkedBlockingQueue<Object>(); for (final Invoker<T> invoker : selected) { executor.execute(new Runnable() { public void run() { try { Result result = invoker.invoke(invocation); ref.offer(result); } catch(Throwable e) { int value = count.incrementAndGet(); if (value >= selected.size()) { ref.offer(e); } } } }); } try { Object ret = ref.poll(timeout, TimeUnit.MILLISECONDS); if (ret instanceof Throwable) { Throwable e = (Throwable) ret; throw new RpcException(e instanceof RpcException ? ((RpcException)e).getCode() : 0, "Failed to forking invoke provider " + selected + ", but no luck to perform the invocation. Last error is: " + e.getMessage(), e.getCause() != null ? e.getCause() : e); } return (Result) ret; } catch (InterruptedException e) { throw new RpcException("Failed to forking invoke provider " + selected + ", but no luck to perform the invocation. Last error is: " + e.getMessage(), e); } } }