/*
* org.openmicroscopy.shoola.util.concur.tasks.ExecutionMonitor
*
*------------------------------------------------------------------------------
* Copyright (C) 2006 University of Dundee. All rights reserved.
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*
*------------------------------------------------------------------------------
*/
package org.openmicroscopy.shoola.util.concur.tasks;
//Java imports
//Third-party libraries
//Application-internal dependencies
/**
* Defines the callbacks that the {@link CmdProcessor} uses to notify observers
* about the state of a given computation.
* The {@link CmdProcessor} allows to register an observer object (observers
* have to implement this interface obviously) for monitoring the execution
* of a computation when the computation is triggered by one of the
* <code>exec</code> methods.
* <p>Notifications are dispatched <i>within the same thread that executes the
* computation</i> and as follows:</p>
* <ol>
* <li>The {@link #onStart() onStart} method is invoked at the beginning
* of the computation before performing the first step in the computation.
* </li>
* <li>The {@link #update(int) update} method is invoked after performing a
* step in the computation.</li>
* <li>Finally when the computation is finished one out of the
* {@link #onEnd(Object) onEnd}, {@link #onAbort(Throwable) onAbort}, or
* {@link #onCancel() onCancel} methods is called, depending on the outcome
* of the computation. If the computation terminates normally, then the
* {@link #onEnd(Object) onEnd} method is called, passing in the result
* of the computation. In the case of failure, the
* {@link #onAbort(Throwable) onAbort} method is called instead, passing
* along the exception that caused the failure. If the computation is
* cancelled, then {@link #onCancel() onCancel} method is called.</li>
* </ol>
* <p>If the {@link CmdProcessor} is executing a {@link java.lang.Runnable} or
* an {@link Invocation}, the computation only consists of one step — the
* execution of the <code>run</code> or <code>call</code> method, respectively.
* In the case of an {@link Invocation} chain or {@link MultiStepTask} a step
* correspond to an invocation of the <code>call</code> or <code>doStep</code>
* method, respectively.</p>
* <p>One thing to keep in mind is that cancelling execution <i>does not</i>
* imply that the {@link #onCancel() onCancel} method will be called. In fact,
* execution could well complete before the cancel signal is detected, in which
* case the {@link #onEnd(Object) onEnd} method would be called instead.</p>
*
* @author Jean-Marie Burel
* <a href="mailto:j.burel@dundee.ac.uk">j.burel@dundee.ac.uk</a>
* @author <br>Andrea Falconi
* <a href="mailto:a.falconi@dundee.ac.uk">
* a.falconi@dundee.ac.uk</a>
* @version 2.2
* <small>
* (<b>Internal version:</b> $Revision$ $Date$)
* </small>
* @since OME2.2
*/
public interface ExecMonitor
{
/**
* Called just before executing the first step in the computation.
*/
public void onStart();
/**
* Called after each step in the computation.
* The passed argument will be <code>1</code> after the first step,
* <code>2</code> after the second step, and so on.
* Note that if the {@link CmdProcessor} is executing a
* {@link java.lang.Runnable} or an {@link Invocation}, the computation
* only consists of one step. In this case, this method is only called
* once with <code>1</code> as argument.
*
* @param step Which step has been executed.
*/
public void update(int step);
/**
* Notifies cancellation.
* The execution terminated because a cancellation signal was received or
* has never started at all.
*/
public void onCancel();
/**
* Notifies failure.
* The execution terminated because of an error.
*
* @param cause The cause of failure.
*/
public void onAbort(Throwable cause);
/**
* Notifies the end of the computation.
* The execution terminated normally. If a result was computed, it is
* passed in — this is the same object that can be retrieved via
* the {@link Future}. Otherwise, <code>null</code> is passed in —
* in the case the computation was encoded as a {@link java.lang.Runnable}.
*
* @param result The result of the computation or <code>null</code> if
* no result was produced.
*/
public void onEnd(Object result);
}