| /******************************************************************************* |
| * Copyright (c) 2012 Oracle. All rights reserved. |
| * This program and the accompanying materials are made available under the |
| * terms of the Eclipse Public License v1.0, which accompanies this distribution |
| * and is available at http://www.eclipse.org/legal/epl-v10.html. |
| * |
| * Contributors: |
| * Oracle - initial API and implementation |
| ******************************************************************************/ |
| package org.eclipse.jpt.common.utility.internal.command; |
| |
| import org.eclipse.jpt.common.utility.command.Command; |
| import org.eclipse.jpt.common.utility.command.StatefulCommandExecutor; |
| import org.eclipse.jpt.common.utility.internal.SimpleQueue; |
| import org.eclipse.jpt.common.utility.internal.StringTools; |
| |
| /** |
| * This is a command executor that queues up any commands that are |
| * {@link #execute(Command) executed} before the executor has been |
| * {@link #start() started} or while the executor is |
| * {@link #suspend() suspended}. These commands will be |
| * executed once the executor is {@link #start() started} or |
| * {@link #resume() resumed}. Once the executor is {@link #start() started}, |
| * all commands are executed <em>synchronously</em>. |
| * Once the executor is {@link #stop() stopped}, no further commands will be |
| * executed; and the executor can<em>not</em> be {@link #start() restarted}. |
| */ |
| public abstract class AbstractSingleUseQueueingCommandExecutor<E extends StatefulCommandExecutor> |
| implements StatefulCommandExecutor |
| { |
| protected final E commandExecutor; |
| private State state; |
| private SimpleQueue<Command> queue = new SimpleQueue<Command>(); |
| |
| private enum State { |
| PRE_START, |
| ACTIVE, |
| SUSPENDED, |
| DEAD |
| } |
| |
| |
| protected AbstractSingleUseQueueingCommandExecutor(E commandExecutor) { |
| super(); |
| if (commandExecutor == null) { |
| throw new NullPointerException(); |
| } |
| this.commandExecutor = commandExecutor; |
| this.state = State.PRE_START; |
| } |
| |
| /** |
| * Start the command executor, executing all the commands that were |
| * queued up since the executor was first constructed. |
| */ |
| public synchronized void start() { |
| if (this.state != State.PRE_START) { |
| throw this.buildISE(); |
| } |
| this.commandExecutor.start(); |
| while ( ! this.queue.isEmpty()) { |
| this.commandExecutor.execute(this.queue.dequeue()); |
| } |
| this.state = State.ACTIVE; |
| } |
| |
| public void execute(Command command) { |
| if (this.commandIsToBeExecuted(command)) { |
| this.commandExecutor.execute(command); |
| } |
| } |
| |
| /** |
| * If the command executor is active (i.e. it has been |
| * {@link #start() started}), execute the specified command. |
| * If the command executor has not been {@link #start() started} or it is |
| * {@link #suspend() suspended}, queue the |
| * command to be executed when the executor is {@link #start() started} or |
| * {@link #resume() resumed}. |
| * If the command executor is dead (i.e. it has been |
| * {@link #stop() stopped}), ignore the command. |
| */ |
| private synchronized boolean commandIsToBeExecuted(Command command) { |
| switch (this.state) { |
| case ACTIVE: |
| // execute the command outside the lock |
| return true; |
| case PRE_START: |
| case SUSPENDED: |
| this.queue.enqueue(command); |
| return false; |
| case DEAD: |
| // ignore |
| return false; |
| } |
| throw this.buildISE(); |
| } |
| |
| /** |
| * Suspend the command executor. Any further requests to |
| * {@link #execute(Command) execute} a command will result in the command |
| * being queued up to be executed once the command executor is |
| * {@link #resume() resumed}. |
| */ |
| public synchronized void suspend() { |
| if (this.state != State.ACTIVE) { |
| throw this.buildISE(); |
| } |
| this.state = State.SUSPENDED; |
| } |
| |
| /** |
| * Resume the command executor, executing all the commands that were |
| * queued up since the executor was {@link #suspend() suspended}. |
| */ |
| public synchronized void resume() { |
| if (this.state != State.SUSPENDED) { |
| throw this.buildISE(); |
| } |
| while ( ! this.queue.isEmpty()) { |
| this.commandExecutor.execute(this.queue.dequeue()); |
| } |
| this.state = State.ACTIVE; |
| } |
| |
| /** |
| * Stop the command executor. Any queued commands (i.e. the commands |
| * {@link #execute(Command) executed} while the command executor had not |
| * been {@link #start() started} or was |
| * {@link #suspend() suspended}) will be ignored. |
| * Any further requests to |
| * {@link #execute(Command) execute} a command will be ignored. |
| * The command executor <em>cannot</em> be {@link #start() restarted}, |
| * {@link #suspend() suspended} or {@link #resume() resumed} once it has |
| * been stopped. |
| */ |
| public synchronized void stop() throws InterruptedException { |
| switch (this.state) { |
| case ACTIVE: |
| // nothing to do |
| break; |
| case SUSPENDED: |
| // drain the queue |
| while ( ! this.queue.isEmpty()) { |
| this.queue.dequeue(); |
| } |
| break; |
| case PRE_START: |
| case DEAD: |
| throw this.buildISE(); |
| } |
| |
| this.commandExecutor.stop(); |
| this.state = State.DEAD; |
| } |
| |
| private IllegalStateException buildISE() { |
| return new IllegalStateException(String.valueOf(this.state)); |
| } |
| |
| @Override |
| public String toString() { |
| return StringTools.buildToStringFor(this, this.state); |
| } |
| } |