/*
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 * SciJava Common shared library for SciJava software.
 * %%
 * Copyright (C) 2009 - 2026 SciJava developers.
 * %%
 * Redistribution and use in source and binary forms, with or without
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 *    this list of conditions and the following disclaimer in the documentation
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 */

package org.scijava.thread;

import java.lang.reflect.InvocationTargetException;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.ThreadFactory;

import org.scijava.Context;
import org.scijava.service.SciJavaService;

/**
 * Interface for the thread handling service.
 *
 * @author Curtis Rueden
 */
public interface ThreadService extends SciJavaService, ThreadFactory {

	public enum ThreadContext {
		/**
		 * The thread was spawned by this thread service; i.e., it belongs to the
		 * same {@link Context}.
		 */
		SAME,

		/**
		 * The thread was spawned by a SciJava thread service, but not this one;
		 * i.e., it belongs to a different {@link Context}.
		 */
		OTHER,

		/**
		 * The thread was not spawned via a SciJava thread service, and its
		 * {@link Context} is unknown or inapplicable.
		 */
		NONE
	}

	/**
	 * Asynchronously executes the given code in a new thread, as decided by the
	 * thread service. Typically this means that the service allocates a thread
	 * from its pool, but ultimately the behavior is implementation-dependent.
	 * This method returns immediately.
	 *
	 * @param code The code to execute.
	 * @return A {@link Future} that will contain the result once the execution
	 *         has finished. Call {@link Future#get()} to access to the return
	 *         value (which will block until execution has completed).
	 */
	<V> Future<V> run(Callable<V> code);

	/**
	 * Asynchronously executes the given code in a new thread, as decided by the
	 * thread service. Typically this means that the service allocates a thread
	 * from its pool, but ultimately the behavior is implementation-dependent.
	 * This method returns immediately.
	 *
	 * @param code The code to execute.
	 * @return A {@link Future} that can be used to block until the execution has
	 *         finished. Call {@link Future#get()} to do so.
	 */
	Future<?> run(Runnable code);

	/**
	 * Gets the {@link ExecutorService} object used when {@link #run} is called.
	 * 
	 * @return the {@link ExecutorService}, or null if an {@link ExecutorService}
	 *         is not used in this {@link ThreadService} implementation.
	 */
	ExecutorService getExecutorService();

	/**
	 * Sets the {@link ExecutorService} object used when {@link #run} is called.
	 * 
	 * @param executor The {@link ExecutorService} for this {@link ThreadService}
	 *          to use internally for {@link #run} calls.
	 * @throws UnsupportedOperationException if this {@link ThreadService} does
	 *           not use an {@link ExecutorService} to handle {@link #run} calls.
	 */
	void setExecutorService(ExecutorService executor);

	/**
	 * Gets whether the current thread is a dispatch thread for use with
	 * {@link #invoke(Runnable)} and {@link #queue(Runnable)}.
	 * <p>
	 * In the case of AWT-based applications (e.g., Java on the desktop), this is
	 * typically the AWT Event Dispatch Thread (EDT). However, ultimately the
	 * behavior is implementation-dependent.
	 * </p>
	 *
	 * @return True iff the current thread is considered a dispatch thread.
	 */
	boolean isDispatchThread();

	/**
	 * Executes the given code in a special dispatch thread, blocking until
	 * execution is complete.
	 * <p>
	 * In the case of AWT-based applications (e.g., Java on the desktop), this is
	 * typically the AWT Event Dispatch Thread (EDT). However, ultimately the
	 * behavior is implementation-dependent.
	 * </p>
	 *
	 * @param code The code to execute.
	 * @throws InterruptedException If the code execution is interrupted.
	 * @throws InvocationTargetException If an uncaught exception occurs in the
	 *           code during execution.
	 */
	void invoke(Runnable code) throws InterruptedException,
		InvocationTargetException;

	/**
	 * Queues the given code for later execution in a special dispatch thread,
	 * returning immediately.
	 * <p>
	 * In the case of AWT-based applications (e.g., Java on the desktop), this is
	 * typically the AWT Event Dispatch Thread (EDT). However, ultimately the
	 * behavior is implementation-dependent.
	 * </p>
	 *
	 * @param code The code to execute.
	 */
	void queue(Runnable code);

	/**
	 * Queues the given code for later execution in a dispatch thread associated
	 * with the specified ID, returning immediately.
	 *
	 * @param id The ID designating which dispatch thread will execute the code.
	 * @param code The code to execute.
	 * @return A {@link Future} whose {@link Future#get()} method blocks until the
	 *         queued code has completed executing and returns {@code null}.
	 * @see ExecutorService#submit(Runnable)
	 */
	Future<?> queue(String id, Runnable code);

	/**
	 * Queues the given code for later execution in a dispatch thread associated
	 * with the specified ID, returning immediately.
	 *
	 * @param id The ID designating which dispatch thread will execute the code.
	 * @param code The code to execute.
	 * @return A {@link Future} whose {@link Future#get()} method blocks until the
	 *         queued code has completed executing and returns the result of the
	 *         execution.
	 * @see ExecutorService#submit(Callable)
	 */
	<V> Future<V> queue(String id, Callable<V> code);

	/**
	 * Returns the thread that called the specified thread.
	 * <p>
	 * This works only on threads which the thread service knows about, of course.
	 * </p>
	 *
	 * @param thread the managed thread, null refers to the current thread
	 * @return the thread that asked the {@link ThreadService} to spawn the
	 *         specified thread
	 */
	Thread getParent(Thread thread);

	/**
	 * Analyzes the {@link Context} of the given thread.
	 *
	 * @param thread The thread to analyze.
	 * @return Information about the thread's {@link Context}. Either:
	 *         <ul>
	 *         <li>{@link ThreadContext#SAME} - The thread was spawned by this
	 *         very thread service, and thus shares the same {@link Context}.</li>
	 *         <li>{@link ThreadContext#OTHER} - The thread was spawned by a
	 *         different thread service, and thus has a different {@link Context}.
	 *         </li>
	 *         <li>{@link ThreadContext#NONE} - It is unknown what spawned the
	 *         thread, so it is effectively {@link Context}-free.</li>
	 *         </ul>
	 */
	ThreadContext getThreadContext(Thread thread);

}
