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Qetcher Java client, OSGi bundle, minimal dependencies

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//
//  ========================================================================
//  Copyright (c) 1995-2018 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.util.thread;

import java.util.concurrent.Callable;

/**
 * A task (typically either a {@link Runnable} or {@link Callable}
 * that declares how it will behave when invoked:
 * 
 * blocking, the invocation will certainly block (e.g. performs blocking I/O)
 * non-blocking, the invocation will certainly not block
 * either, the invocation may block
 * 
 * 
 * 
 * Static methods and are provided that allow the current thread to be tagged 
 * with a {@link ThreadLocal} to indicate if it has a blocking invocation type.
 * 
 * 
 */
public interface Invocable
{
    enum InvocationType
    {
        BLOCKING, NON_BLOCKING, EITHER
    }

    static ThreadLocal __nonBlocking = new ThreadLocal<>();

    /**
     * Test if the current thread has been tagged as non blocking
     * @return True if the task the current thread is running has
     * indicated that it will not block.
     */
    public static boolean isNonBlockingInvocation()
    {
        return Boolean.TRUE.equals(__nonBlocking.get());
    }

    /**
     * Invoke a task with the calling thread, tagged to indicate
     * that it will not block.
     * @param task The task to invoke.
     */
    public static void invokeNonBlocking(Runnable task)
    {
        Boolean was_non_blocking = __nonBlocking.get();
        try
        {
            __nonBlocking.set(Boolean.TRUE);
            task.run();
        }
        finally
        {
            __nonBlocking.set(was_non_blocking);
        }
    }

    /**
     * Get the invocation type of an Object.
     * @param o The object to check the invocation type of.
     * @return If the object is an Invocable, it is coerced and the {@link #getInvocationType()}
     * used, otherwise {@link InvocationType#BLOCKING} is returned.
     */
    public static InvocationType getInvocationType(Object o)
    {
        if (o instanceof Invocable)
            return ((Invocable)o).getInvocationType();
        return InvocationType.BLOCKING;
    }

    /**
     * @return The InvocationType of this object
     */
    default InvocationType getInvocationType()
    {
        return InvocationType.BLOCKING;
    }
}