Copyright 2012 Netflix, Inc.
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.
/**
 * Copyright 2012 Netflix, Inc.
 * 
 * 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.netflix.hystrix.strategy.concurrency;

import java.util.concurrent.Callable;

import com.netflix.hystrix.strategy.HystrixPlugins;

Wrapper around Callable that manages the HystrixRequestContext initialization and cleanup for the execution of the Callable 
Type parameters:
<K> –  Return type of Callable
@ExcludeFromJavadoc
/**
 * Wrapper around {@link Callable} that manages the {@link HystrixRequestContext} initialization and cleanup for the execution of the {@link Callable}
 * 
 * @param <K>
 *            Return type of {@link Callable}
 * 
 * @ExcludeFromJavadoc
 */
public class HystrixContextCallable<K> implements Callable<K> {

    private final Callable<K> actual;
    private final HystrixRequestContext parentThreadState;

    public HystrixContextCallable(Callable<K> actual) {
        this(HystrixPlugins.getInstance().getConcurrencyStrategy(), actual);
    }

    public HystrixContextCallable(HystrixConcurrencyStrategy concurrencyStrategy, Callable<K> actual) {
        this.actual = concurrencyStrategy.wrapCallable(actual);
        this.parentThreadState = HystrixRequestContext.getContextForCurrentThread();
    }

    @Override
    public K call() throws Exception {
        HystrixRequestContext existingState = HystrixRequestContext.getContextForCurrentThread();
        try {
            // set the state of this thread to that of its parent
            HystrixRequestContext.setContextOnCurrentThread(parentThreadState);
            // execute actual Callable with the state of the parent
            return actual.call();
        } finally {
            // restore this thread back to its original state
            HystrixRequestContext.setContextOnCurrentThread(existingState);
        }
    }

}