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package org.scijava.task;

import java.util.concurrent.ExecutionException;

import java.util.concurrent.Future;

import org.scijava.event.EventService;

import org.scijava.task.event.TaskEvent;

import org.scijava.thread.ThreadService;

/**

* Default implementation of {@link Task}. Throughout the task (or job),

* {@link Task#setProgressValue(long)} can be called to inform

* how the job is progressing.

* <p>

* Asynchronous case:

* A job (runnable) is sent for execution to the linked {@link ThreadService}.

* It reports status updates via the linked {@link EventService}.

* A {@link org.scijava.task.event.TaskEvent} is sent before the job

* is started and when finished.

* In the asynchronous case, upon task cancellation ({@link Task#cancel(String)} call),

* the runnable associated to the ThreadService is attempted to be stopped

* by calling {@link Future#cancel(boolean)}.

* This default behaviour can be supplemented by an additional

* custom callback which can be set in {@link Task#setCancelCallBack(Runnable)}.

* </p>

* <p>

* Synchronous case:

* A job that reports its status in between calls of {@link Task#start()},

* and {@link Task#finish()}. It also reports its status via

* the linked {@link EventService}.

* Start and finish calls allow publishing proper {@link org.scijava.task.event.TaskEvent}

* to subscribers (with the EventService).

* Upon cancellation of a synchronous task, it is the responsibility

* of the synchronous task to handle its own cancellation through

* a custom callback which can be set via {@link Task#setCancelCallBack(Runnable)}.

* </p>

*

* @author Curtis Rueden

* @author Nicolas Chiaruttini

*/

public class DefaultTask implements Task {

private final ThreadService threadService;

private final EventService eventService;

private Future<?> future;

private boolean canceled;

private String cancelReason;

volatile boolean isDone = false;

private String status;

private long step;

private long max;

private String name;

private Runnable cancelCallBack;

/**

* Creates a new task.

*

* @param threadService Service to use for launching the task in its own

* thread. Required.

* @param eventService Service to use for reporting status updates as

* {@link TaskEvent}s. May be null, in which case no events are

* reported.

*/

public DefaultTask(final ThreadService threadService,

final EventService eventService)

{

this.threadService = threadService;

this.eventService = eventService;

cancelCallBack = this::defaultCancelCallback;

}

// -- Task methods --

// - Asynchronous

@Override

public void run(final Runnable r) {

if (r == null) throw new NullPointerException();

future(r);

}

// - Asynchronous

@Override

public void waitFor() throws InterruptedException, ExecutionException {

future().get();

}

// - Synchronous

@Override

public void start() {

fireTaskEvent();

}

// - Synchronous

@Override

public void finish() {

isDone = true;

fireTaskEvent();

}

@Override

public boolean isDone() {

return (isDone) || (future != null && future.isDone());

}

@Override

public String getStatusMessage() {

return status;

}

@Override

public long getProgressValue() {

return step;

}

@Override

public long getProgressMaximum() {

return max;

}

@Override

public void setStatusMessage(final String status) {

this.status = status;

fireTaskEvent();

}

@Override

public void setProgressValue(final long step) {

this.step = step;

fireTaskEvent();

}

@Override

public void setProgressMaximum(final long max) {

this.max = max;

fireTaskEvent();

}

// -- Cancelable methods --

@Override

public boolean isCanceled() {

return canceled;

}

@Override

public void cancel(final String reason) {

canceled = true;

cancelReason = reason;

if (cancelCallBack != null) cancelCallBack.run();

fireTaskEvent();

}

void defaultCancelCallback() {

if (future != null) {

isDone = future.cancel(true);

}

}

@Override

public void setCancelCallBack(Runnable r) {

this.cancelCallBack = r;

}

@Override

public Runnable getCancelCallBack() {

return this.cancelCallBack;

}

@Override

public String getCancelReason() {

return cancelReason;

}

// -- Named methods --

@Override

public String getName() {

return name;

}

@Override

public void setName(final String name) {

this.name = name;

}

// -- Helper methods --

private Future<?> future() {

return future(null);

}

private Future<?> future(final Runnable r) {

if (future == null) initFuture(r);

return future;

}

private synchronized void initFuture(final Runnable r) {

if (future != null) return;

if (r == null) throw new IllegalArgumentException("Must call run first");

future = threadService.run(() -> {

try {

fireTaskEvent(); // Triggers an event just before the task is executed

r.run();

}

finally {

isDone = true;

fireTaskEvent(); // Triggers an event just after the task has

// successfully completed or failed

}

});

}

private void fireTaskEvent() {

if (eventService != null) eventService.publish(new TaskEvent(this));

}

}