dubbo FutureContext 源码

dubbo FutureContext 代码

文件路径：/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/FutureContext.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.dubbo.rpc;

import org.apache.dubbo.common.constants.CommonConstants;
import org.apache.dubbo.common.threadlocal.InternalThreadLocal;
import org.apache.dubbo.rpc.protocol.dubbo.FutureAdapter;

import java.util.concurrent.CompletableFuture;

/**
 * Used for async call scenario. But if the method you are calling has a {@link CompletableFuture<?>} signature
 * you do not need to use this class since you will get a Future response directly.
 * <p>
 * Remember to save the Future reference before making another call using the same thread, otherwise,
 * the current Future will be override by the new one, which means you will lose the chance get the return value.
 */
public class FutureContext {

    private static InternalThreadLocal<FutureContext> futureTL = new InternalThreadLocal<FutureContext>() {
        @Override
        protected FutureContext initialValue() {
            return new FutureContext();
        }
    };

    public static FutureContext getContext() {
        return futureTL.get();
    }

    private CompletableFuture<?> future;
    private CompletableFuture<?> compatibleFuture;

    /**
     * Whether clear future once get
     */
    private final static boolean clearFutureAfterGet = Boolean.parseBoolean(System.getProperty(CommonConstants.CLEAR_FUTURE_AFTER_GET, "false"));

    /**
     * get future.
     *
     * @param <T>
     * @return future
     */
    @SuppressWarnings("unchecked")
    public <T> CompletableFuture<T> getCompletableFuture() {
        try {
            return (CompletableFuture<T>) future;
        } finally {
            if (clearFutureAfterGet) {
                this.future = null;
            }
        }
    }

    /**
     * set future.
     *
     * @param future
     */
    public void setFuture(CompletableFuture<?> future) {
        this.future = future;
    }

    @Deprecated
    @SuppressWarnings("unchecked")
    public <T> CompletableFuture<T> getCompatibleCompletableFuture() {
        try {
            return (CompletableFuture<T>) compatibleFuture;
        } finally {
            if (clearFutureAfterGet) {
                this.compatibleFuture = null;
            }
        }
    }

    /**
     * Guarantee 'using org.apache.dubbo.rpc.RpcContext.getFuture() before proxy returns' can work, a typical scenario is:
     * <pre>{@code
     *      public final class TracingFilter implements Filter {
     *          public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
     *              Result result = invoker.invoke(invocation);
     *              Future<Object> future = rpcContext.getFuture();
     *              if (future instanceof FutureAdapter) {
     *                  ((FutureAdapter) future).getFuture().setCallback(new FinishSpanCallback(span));
     *               }
     *              ......
     *          }
     *      }
     * }</pre>
     *
     * Start from 2.7.3, you don't have to get Future from RpcContext, we recommend using Result directly:
     * <pre>{@code
     *      public final class TracingFilter implements Filter {
     *          public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
     *              Result result = invoker.invoke(invocation);
     *              result.getResponseFuture().whenComplete(new FinishSpanCallback(span));
     *              ......
     *          }
     *      }
     * }</pre>
     *
     */
    @Deprecated
    public void setCompatibleFuture(CompletableFuture<?> compatibleFuture) {
        this.compatibleFuture = compatibleFuture;
        if (compatibleFuture != null) {
            this.setFuture(new FutureAdapter(compatibleFuture));
        }
    }

}

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