com.amazonaws.services.simpleworkflow.flow.WorkflowExecutionLocal Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of aws-java-sdk Show documentation

The Amazon Web Services SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

The newest version!

/*
 * Copyright 2012-2014 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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.amazonaws.services.simpleworkflow.flow;

import java.util.ArrayList;
import java.util.List;

/**
 * Contains value that is bound to a currently executing workflow. Has the same
 * purpose as {@link ThreadLocal} which bounds value to a particular thread. It
 * is subject to the same replay rules as the rest of the workflow definition.
 */
public class WorkflowExecutionLocal {

    private static class Wrapper {

        public T wrapped;
    }

    /**
     * It is not good idea to rely on the fact that implementation relies on
     * ThreadLocal as it is subject to change.
     */
    private final ThreadLocal> value = new ThreadLocal>();

    private final static List> locals = new ArrayList>();

    /**
     * Must be called before each decision. It is not a good idea to call this
     * method from non framework code for non testing scenarios.
     */
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static void before() {
        List> currentLocals;
        synchronized (locals) {
            currentLocals = new ArrayList>(locals);
        }
        for (WorkflowExecutionLocal local : currentLocals) {
            Wrapper w = new Wrapper();
            w.wrapped = local.initialValue();
            local.set(w);
        }
    }

    /**
     * Must be called at the end of each decision. It is not a good idea to call
     * this method from non framework code for non testing scenarios.
     */
    public static void after() {
        List> currentLocals;
        synchronized (locals) {
            currentLocals = new ArrayList>(locals);
        }
        for (WorkflowExecutionLocal local : currentLocals) {
            local.removeAfter();
        }
    }

    @SuppressWarnings({ "unchecked", "rawtypes" })
    public WorkflowExecutionLocal() {
        Wrapper w = new Wrapper();
        w.wrapped = initialValue();
        set(w);
        synchronized (locals) {
            locals.add(this);
        }
    }

    public T get() {
        Wrapper w = getWrapped();
        return w.wrapped;
    }

    private Wrapper getWrapped() {
        Wrapper w = value.get();
        if (w == null) {
            throw new IllegalStateException("Called outside of the workflow definition code.");
        }
        return w;
    }

    public int hashCode() {
        Wrapper w = getWrapped();
        return w.wrapped.hashCode();
    }

    public void remove() {
        Wrapper w = getWrapped();
        w.wrapped = null;
    }

    public void set(T v) {
        Wrapper w = getWrapped();
        w.wrapped = v;
    }

    private void set(Wrapper w) {
        value.set(w);
    }
    
    private void removeAfter() {
        value.remove();
    }
    
    protected T initialValue() {
        return null;
    }

}