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SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by downstream projects in the SciJava ecosystem, such as ImageJ and SCIFIO.
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/*
 * #%L
 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2016 Board of Regents of the University of
 * Wisconsin-Madison, Broad Institute of MIT and Harvard, and Max Planck
 * Institute of Molecular Cell Biology and Genetics.
 * %%
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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 * #L%
 */

package org.scijava.thread;

import java.awt.EventQueue;
import java.lang.reflect.InvocationTargetException;
import java.util.WeakHashMap;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

import org.scijava.log.LogService;
import org.scijava.plugin.Parameter;
import org.scijava.plugin.Plugin;
import org.scijava.service.AbstractService;
import org.scijava.service.Service;

/**
 * Default service for managing active threads.
 * 
 * @author Curtis Rueden
 */
@Plugin(type = Service.class)
public final class DefaultThreadService extends AbstractService implements
	ThreadService
{

	private static final String SCIJAVA_THREAD_PREFIX = "SciJava-";

	private static WeakHashMap parents =
		new WeakHashMap<>();

	@Parameter
	private LogService log;

	private ExecutorService executor;

	private int nextThread = 0;

	private boolean disposed;

	// -- ThreadService methods --

	@Override
	public  Future run(final Callable code) {
		if (disposed) return null;
		return executor().submit(wrap(code));
	}

	@Override
	public Future run(final Runnable code) {
		if (disposed) return null;
		return executor().submit(wrap(code));
	}

	@Override
	public ExecutorService getExecutorService() {
		return executor();
	}

	@Override
	public void setExecutorService(final ExecutorService executor) {
		this.executor = executor;
	}

	@Override
	public boolean isDispatchThread() {
		return EventQueue.isDispatchThread();
	}

	@Override
	public void invoke(final Runnable code) throws InterruptedException,
		InvocationTargetException
	{
		if (isDispatchThread()) {
			// just call the code
			code.run();
		}
		else {
			// invoke on the EDT
			EventQueue.invokeAndWait(wrap(code));
		}
	}

	@Override
	public void queue(final Runnable code) {
		EventQueue.invokeLater(wrap(code));
	}

	@Override
	public Thread getParent(final Thread thread) {
		return parents.get(thread != null ? thread : Thread.currentThread());
	}

	@Override
	public ThreadContext getThreadContext(final Thread thread) {
		final String name = thread.getName();

		// check for same context
		if (name.startsWith(contextThreadPrefix())) return ThreadContext.SAME;

		// check for different context
		if (name.startsWith(SCIJAVA_THREAD_PREFIX)) return ThreadContext.OTHER;

		// recursively check parent thread
		final Thread parent = getParent(thread);
		if (parent == thread || parent == null) return ThreadContext.NONE;
		return getThreadContext(parent);
	}

	// -- Disposable methods --

	@Override
	public void dispose() {
		disposed = true;
		if (executor != null) executor.shutdown();
	}

	// -- ThreadFactory methods --

	@Override
	public Thread newThread(final Runnable r) {
		final String threadName = contextThreadPrefix() + nextThread++;
		return new Thread(r, threadName);
	}

	// -- Helper methods --

	private ExecutorService executor() {
		if (executor == null) {
			executor = Executors.newCachedThreadPool(this);
		}
		return executor;
	}

	private Runnable wrap(final Runnable r) {
		final Thread parent = Thread.currentThread();
		return new Runnable() {
			@Override
			public void run() {
				final Thread thread = Thread.currentThread();
				try {
					if (parent != thread) parents.put(thread, parent);
					r.run();
				}
				finally {
					if (parent != thread) parents.remove(thread);
				}
			}
		};
	}

	private  Callable wrap(final Callable c) {
		final Thread parent = Thread.currentThread();
		return new Callable() {
			@Override
			public V call() throws Exception {
				final Thread thread = Thread.currentThread();
				try {
					if (parent != thread) parents.put(thread, parent);
					return c.call();
				}
				finally {
					if (parent != thread) parents.remove(thread);
				}
			}
		};
	}

	private String contextThreadPrefix() {
		final String contextHash = Integer.toHexString(context().hashCode());
		return SCIJAVA_THREAD_PREFIX + contextHash + "-Thread-";
	}

}