Add supervisor/task library in.

pom.xml

@@ -199,15 +199,6 @@
       <optional>true</optional>
     </dependency>
 
-    <dependency>
-      <groupId>com.sk89q</groupId>
-      <artifactId>odeum</artifactId>
-      <version>0.2.0-SNAPSHOT</version>
-      <scope>compile</scope>
-      <type>jar</type>
-      <optional>true</optional>
-    </dependency>
-
     <dependency>
       <groupId>junit</groupId>
       <artifactId>junit</artifactId>
@@ -400,7 +391,6 @@
                   <include>com.jolbox:bonecp</include>
                   <include>org.flywaydb:flyway-core</include>
                   <include>com.sk89q:squirrelid</include>
-                  <include>com.sk89q:odeum</include>
                 </includes>
               </artifactSet>
               <relocations>
@@ -416,10 +406,6 @@
                   <pattern>com.sk89q.squirrelid</pattern>
                   <shadedPattern>com.sk89q.worldguard.util.profile</shadedPattern>
                 </relocation>
-                <relocation>
-                  <pattern>com.sk89q.odeum</pattern>
-                  <shadedPattern>com.sk89q.worldguard.internal.odeum</shadedPattern>
-                </relocation>
               </relocations>
             </configuration>
           </execution>

src/main/java/com/sk89q/worldguard/bukkit/WorldGuardPlugin.java

@@ -30,10 +30,10 @@
 import com.sk89q.minecraft.util.commands.MissingNestedCommandException;
 import com.sk89q.minecraft.util.commands.SimpleInjector;
 import com.sk89q.minecraft.util.commands.WrappedCommandException;
-import com.sk89q.odeum.concurrent.EvenMoreExecutors;
-import com.sk89q.odeum.task.SimpleSupervisor;
-import com.sk89q.odeum.task.Supervisor;
-import com.sk89q.odeum.task.Task;
+import com.sk89q.worldguard.util.concurrent.EvenMoreExecutors;
+import com.sk89q.worldguard.util.task.SimpleSupervisor;
+import com.sk89q.worldguard.util.task.Supervisor;
+import com.sk89q.worldguard.util.task.Task;
 import com.sk89q.squirrelid.cache.HashMapCache;
 import com.sk89q.squirrelid.cache.ProfileCache;
 import com.sk89q.squirrelid.cache.SQLiteCache;

src/main/java/com/sk89q/worldguard/bukkit/commands/AsyncCommandHelper.java

@@ -21,7 +21,7 @@
 
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
-import com.sk89q.odeum.task.FutureForwardingTask;
+import com.sk89q.worldguard.util.task.FutureForwardingTask;
 import com.sk89q.worldguard.bukkit.WorldGuardPlugin;
 import org.bukkit.World;
 import org.bukkit.command.CommandSender;

src/main/java/com/sk89q/worldguard/bukkit/commands/WorldGuardCommands.java

@@ -23,14 +23,13 @@
 import com.sk89q.minecraft.util.commands.CommandContext;
 import com.sk89q.minecraft.util.commands.CommandException;
 import com.sk89q.minecraft.util.commands.CommandPermissions;
-import com.sk89q.odeum.task.Task;
-import com.sk89q.odeum.task.TaskStateComparator;
+import com.sk89q.worldguard.util.task.Task;
+import com.sk89q.worldguard.util.task.TaskStateComparator;
 import com.sk89q.worldguard.bukkit.util.LoggerToChatHandler;
 import com.sk89q.worldguard.bukkit.util.ReportWriter;
 import com.sk89q.worldguard.bukkit.WorldGuardPlugin;
 import com.sk89q.worldguard.util.PastebinPoster;
 import com.sk89q.worldguard.util.PastebinPoster.PasteCallback;
-import org.bukkit.Bukkit;
 import org.bukkit.ChatColor;
 import org.bukkit.command.CommandSender;
 import org.bukkit.entity.Player;

src/main/java/com/sk89q/worldguard/protection/managers/index/ChunkHashTable.java

@@ -23,7 +23,7 @@
 import com.google.common.base.Supplier;
 import com.google.common.util.concurrent.ListeningExecutorService;
 import com.google.common.util.concurrent.MoreExecutors;
-import com.sk89q.odeum.concurrent.EvenMoreExecutors;
+import com.sk89q.worldguard.util.concurrent.EvenMoreExecutors;
 import com.sk89q.worldedit.Vector;
 import com.sk89q.worldedit.Vector2D;
 import com.sk89q.worldguard.protection.managers.RegionDifference;

src/main/java/com/sk89q/worldguard/util/concurrent/EvenMoreExecutors.java

@@ -0,0 +1,54 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.concurrent;
+
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.LinkedBlockingDeque;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Provides additional executors.
+ */
+public final class EvenMoreExecutors {
+
+    private EvenMoreExecutors() {
+    }
+
+    /**
+     * Creates a thread pool that creates new threads as needed up to
+     * a maximum number of threads, but will reuse previously constructed
+     * threads when they are available.
+     *
+     * @param minThreads the minimum number of threads to have at a given time
+     * @param maxThreads the maximum number of threads to have at a given time
+     * @param queueSize the size of the queue before new submissions are rejected
+     * @return the newly created thread pool
+     */
+    public static ExecutorService newBoundedCachedThreadPool(int minThreads, int maxThreads, int queueSize) {
+        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(
+                minThreads, maxThreads,
+                60L, TimeUnit.SECONDS,
+                new LinkedBlockingDeque<Runnable>(queueSize));
+        threadPoolExecutor.allowCoreThreadTimeOut(true);
+        return threadPoolExecutor;
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/AbstractTask.java

@@ -0,0 +1,74 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import com.google.common.util.concurrent.AbstractFuture;
+
+import javax.annotation.Nullable;
+import java.util.Date;
+import java.util.UUID;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * An abstract task that stores a name and owner.
+ *
+ * @param <V> the type returned
+ */
+public abstract class AbstractTask<V> extends AbstractFuture<V> implements Task<V> {
+
+    private final UUID uniqueId = UUID.randomUUID();
+    private final String name;
+    private final Object owner;
+    private final Date creationDate = new Date();
+
+    /**
+     * Create a new instance.
+     *
+     * @param name the name
+     * @param owner the owner
+     */
+    protected AbstractTask(String name, @Nullable Object owner) {
+        checkNotNull(name);
+        this.name = name;
+        this.owner = owner;
+    }
+
+    @Override
+    public UUID getUniqueId() {
+        return uniqueId;
+    }
+
+    @Override
+    public String getName() {
+        return name;
+    }
+
+    @Nullable
+    @Override
+    public Object getOwner() {
+        return owner;
+    }
+
+    @Override
+    public Date getCreationDate() {
+        return creationDate;
+    }
+}

src/main/java/com/sk89q/worldguard/util/task/FutureForwardingTask.java

@@ -0,0 +1,121 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.sk89q.worldguard.util.task.progress.Progress;
+
+import javax.annotation.Nullable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Executor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * A task that wraps a {@code ListenableFuture}.
+ *
+ * <p>{@link State#SCHEDULED} is never returned because it is not possible
+ * to test whether the future has "started," so {@link State#RUNNING} is
+ * returned in its place.</p>
+ *
+ * <p>Use {@link #create(ListenableFuture, String, Object)} to create a new
+ * instance.</p>
+ *
+ * @param <V> the type returned
+ */
+public class FutureForwardingTask<V> extends AbstractTask<V> {
+
+    private final ListenableFuture<V> future;
+
+    private FutureForwardingTask(ListenableFuture<V> future, String name, @Nullable Object owner) {
+        super(name, owner);
+        checkNotNull(future);
+        this.future = future;
+    }
+
+    @Override
+    public void addListener(Runnable listener, Executor executor) {
+        future.addListener(listener, executor);
+    }
+
+    @Override
+    public boolean cancel(boolean mayInterruptIfRunning) {
+        return future.cancel(mayInterruptIfRunning);
+    }
+
+    @Override
+    public boolean isCancelled() {
+        return future.isCancelled();
+    }
+
+    @Override
+    public boolean isDone() {
+        return future.isDone();
+    }
+
+    @Override
+    public V get() throws InterruptedException, ExecutionException {
+        return future.get();
+    }
+
+    @Override
+    public V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
+        return future.get(timeout, unit);
+    }
+
+    @Override
+    public State getState() {
+        if (isCancelled()) {
+            return State.CANCELLED;
+        } else if (isDone()) {
+            try {
+                get();
+                return State.SUCCEEDED;
+            } catch (InterruptedException e) {
+                return State.CANCELLED;
+            } catch (ExecutionException e) {
+                return State.FAILED;
+            }
+        } else {
+            return State.RUNNING;
+        }
+    }
+
+    @Override
+    public Progress getProgress() {
+        return Progress.indeterminate();
+    }
+
+    /**
+     * Create a new instance.
+     *
+     * @param future the future
+     * @param name the name of the task
+     * @param owner the owner of the task, or {@code null}
+     * @param <V> the type returned by the future
+     * @return a new instance
+     */
+    public static <V> com.sk89q.worldguard.util.task.FutureForwardingTask<V> create(ListenableFuture<V> future, String name, @Nullable Object owner) {
+        return new com.sk89q.worldguard.util.task.FutureForwardingTask<V>(future, name, owner);
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/SimpleSupervisor.java

@@ -0,0 +1,62 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import com.google.common.util.concurrent.MoreExecutors;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * An implementation of a {@code Supervisor}.
+ */
+public class SimpleSupervisor implements Supervisor {
+
+    private final List<Task<?>> monitored = new ArrayList<Task<?>>();
+    private final Object lock = new Object();
+
+    @Override
+    public List<Task<?>> getTasks() {
+        synchronized (lock) {
+            return new ArrayList<Task<?>>(monitored);
+        }
+    }
+
+    @Override
+    public void monitor(final Task<?> task) {
+        checkNotNull(task);
+
+        synchronized (lock) {
+            monitored.add(task);
+        }
+
+        task.addListener(new Runnable() {
+            @Override
+            public void run() {
+                synchronized (lock) {
+                    monitored.remove(task);
+                }
+            }
+        }, MoreExecutors.sameThreadExecutor());
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/Supervisor.java

@@ -0,0 +1,44 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import java.util.List;
+
+/**
+ * Manages running tasks and informs users of their progress, but does not
+ * execute the task.
+ */
+public interface Supervisor {
+
+    /**
+     * Get a list of running or queued tasks.
+     *
+     * @return a list of tasks
+     */
+    List<Task<?>> getTasks();
+
+    /**
+     * Monitor the given task.
+     *
+     * @param task the task
+     */
+    void monitor(Task<?> task);
+
+}

src/main/java/com/sk89q/worldguard/util/task/Task.java

@@ -0,0 +1,97 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.sk89q.worldguard.util.task.progress.ProgressObservable;
+
+import javax.annotation.Nullable;
+import java.util.Date;
+import java.util.UUID;
+
+/**
+ * A task is a job that can be scheduled, run, or cancelled. Tasks can report
+ * on their own status. Tasks have owners.
+ */
+public interface Task<V> extends ListenableFuture<V>, ProgressObservable {
+
+    /**
+     * Get the unique ID of this task.
+     *
+     * @return this task's unique ID
+     */
+    UUID getUniqueId();
+
+    /**
+     * Get the name of the task so it can be printed to the user.
+     *
+     * @return the name of the task
+     */
+    String getName();
+
+    /**
+     * Get the owner of the task.
+     *
+     * @return an owner object, if one is known or valid, otherwise {@code null}
+     */
+    @Nullable
+    Object getOwner();
+
+    /**
+     * Get the state of the task.
+     *
+     * @return the state of the task
+     */
+    State getState();
+
+    /**
+     * Get the time at which the task was created.
+     *
+     * @return a date
+     */
+    Date getCreationDate();
+
+    /**
+     * Represents the state of a task.
+     */
+    public enum State {
+        /**
+         * The task has been scheduled to run but is not running yet.
+         */
+        SCHEDULED,
+        /**
+         * The task has been cancelled and may be stopped or will stop.
+         */
+        CANCELLED,
+        /**
+         * The task is currently running.
+         */
+        RUNNING,
+        /**
+         * The task has failed.
+         */
+        FAILED,
+        /**
+         * The task has succeeded.
+         */
+        SUCCEEDED
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/TaskStateComparator.java

@@ -0,0 +1,43 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task;
+
+import java.util.Comparator;
+
+/**
+ * Compares task states according to the order of the {@link com.sk89q.worldguard.util.task.Task.State}
+ * enumeration.
+ */
+public class TaskStateComparator implements Comparator<com.sk89q.worldguard.util.task.Task<?>> {
+
+    @Override
+    public int compare(com.sk89q.worldguard.util.task.Task<?> o1, Task<?> o2) {
+        int ordinal1 = o1.getState().ordinal();
+        int ordinal2 = o2.getState().ordinal();
+        if (ordinal1 < ordinal2) {
+            return -1;
+        } else if (ordinal1 > ordinal2) {
+            return 1;
+        } else {
+            return 0;
+        }
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/progress/Progress.java

@@ -0,0 +1,183 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task.progress;
+
+import java.util.Arrays;
+import java.util.Collection;
+
+/**
+ * A progress object describes the progress of an operation, specifying
+ * either a percentage of completion or a status of indeterminacy.
+ *
+ * <p>Progress objects are immutable.</p>
+ *
+ * <p>To create a new instance, use one of the static constructors
+ * on this class.</p>
+ */
+public abstract class Progress {
+
+    /**
+     * Create a new instance.
+     */
+    private Progress() {
+    }
+
+    /**
+     * Return whether the current progress is indeterminate.
+     *
+     * @return true if indeterminate
+     */
+    public abstract boolean isIndeterminate();
+
+    /**
+     * Get the progress percentage.
+     *
+     * <p>If {@link #isIndeterminate()} returns {@code true}, the behavior
+     * of this method is undefined.</p>
+     *
+     * @return a number in the range [0, 1]
+     */
+    public abstract double getProgress();
+
+    /**
+     * Get a static progress object that is indeterminate.
+     *
+     * @return a progress object
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress indeterminate() {
+        return INDETERMINATE;
+    }
+
+    /**
+     * Get a static progress object that is complete.
+     *
+     * @return a progress object
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress completed() {
+        return COMPLETED;
+    }
+
+    /**
+     * Create a new progress object with the given percentage.
+     *
+     * @param value the percentage, which will be clamped to [0, 1]
+     * @return a progress object
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress of(double value) {
+        if (value < 0) {
+            value = 0;
+        } else if (value > 1) {
+            value = 1;
+        }
+
+        final double finalValue = value;
+        return new com.sk89q.worldguard.util.task.progress.Progress() {
+            @Override
+            public boolean isIndeterminate() {
+                return false;
+            }
+
+            @Override
+            public double getProgress() {
+                return finalValue;
+            }
+        };
+    }
+
+    /**
+     * Create a new progress object with progress split equally between the
+     * given progress objects.
+     *
+     * @param objects an array of progress objects
+     * @return a new progress value
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress split(com.sk89q.worldguard.util.task.progress.Progress... objects) {
+        return split(Arrays.asList(objects));
+    }
+
+    /**
+     * Create a new progress object with progress split equally between the
+     * given progress objects.
+     *
+     * @param progress a collection of progress objects
+     * @return a new progress value
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress split(Collection<com.sk89q.worldguard.util.task.progress.Progress> progress) {
+        int count = 0;
+        double total = 0;
+
+        for (com.sk89q.worldguard.util.task.progress.Progress p : progress) {
+            if (p.isIndeterminate()) {
+                return indeterminate();
+            }
+            total += p.getProgress();
+        }
+
+        return of(total / count);
+    }
+
+    /**
+     * Create a new progress object with progress split equally between the
+     * given {@link com.sk89q.worldguard.util.task.progress.ProgressObservable}s.
+     *
+     * @param observables an array of observables
+     * @return a new progress value
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress splitObservables(com.sk89q.worldguard.util.task.progress.ProgressObservable... observables) {
+        return splitObservables(Arrays.asList(observables));
+    }
+
+    /**
+     * Create a new progress object with progress split equally between the
+     * given {@link com.sk89q.worldguard.util.task.progress.ProgressObservable}s.
+     *
+     * @param observables a collection of observables
+     * @return a new progress value
+     */
+    public static com.sk89q.worldguard.util.task.progress.Progress splitObservables(Collection<? extends com.sk89q.worldguard.util.task.progress.ProgressObservable> observables) {
+        int count = 0;
+        double total = 0;
+
+        for (ProgressObservable observable : observables) {
+            com.sk89q.worldguard.util.task.progress.Progress p = observable.getProgress();
+            if (p.isIndeterminate()) {
+                return indeterminate();
+            }
+            total += p.getProgress();
+        }
+
+        return of(total / count);
+    }
+
+    private static final com.sk89q.worldguard.util.task.progress.Progress COMPLETED = of(1);
+
+    private static final com.sk89q.worldguard.util.task.progress.Progress INDETERMINATE = new com.sk89q.worldguard.util.task.progress.Progress() {
+        @Override
+        public boolean isIndeterminate() {
+            return true;
+        }
+
+        @Override
+        public double getProgress() {
+            return 0;
+        }
+    };
+
+}

src/main/java/com/sk89q/worldguard/util/task/progress/ProgressIterator.java

@@ -0,0 +1,100 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task.progress;
+
+import java.util.Iterator;
+import java.util.List;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * An iterator that keeps track of how many entries have been visited and
+ * calculates a "percent completed" using a provided total count.
+ *
+ * <p>The returned progress percentage will always be between 0 or 1
+ * (inclusive). If the iterator returns more entries than the total count,
+ * then 100% will be returned for the progress.</p>
+ *
+ * @param <V> the type
+ */
+public class ProgressIterator<V> implements Iterator<V>, ProgressObservable {
+
+    private final Iterator<V> iterator;
+    private final int count;
+    private int visited = 0;
+
+    /**
+     * Create a new instance.
+     *
+     * @param iterator the iterator
+     * @param count the count
+     */
+    private ProgressIterator(Iterator<V> iterator, int count) {
+        checkNotNull(iterator);
+        this.iterator = iterator;
+        this.count = count;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return iterator.hasNext();
+    }
+
+    @Override
+    public V next() {
+        V value = iterator.next();
+        visited++;
+        return value;
+    }
+
+    @Override
+    public void remove() {
+        iterator.remove();
+    }
+
+    @Override
+    public Progress getProgress() {
+        return Progress.of(count > 0 ? Math.min(1, Math.max(0, (visited / (double) count))) : 1);
+    }
+
+    /**
+     * Create a new instance.
+     *
+     * @param iterator the iterator
+     * @param count the number of objects
+     * @param <V> the type
+     * @return an instance
+     */
+    public static <V> com.sk89q.worldguard.util.task.progress.ProgressIterator<V> create(Iterator<V> iterator, int count) {
+        return new com.sk89q.worldguard.util.task.progress.ProgressIterator<V>(iterator, count);
+    }
+
+    /**
+     * Create a new instance from a list.
+     *
+     * @param list a list
+     * @param <V> the type
+     * @return an instance
+     */
+    public static <V> com.sk89q.worldguard.util.task.progress.ProgressIterator<V> create(List<V> list) {
+        return create(list.iterator(), list.size());
+    }
+
+}

src/main/java/com/sk89q/worldguard/util/task/progress/ProgressObservable.java

@@ -0,0 +1,34 @@
+/*
+ * WorldGuard, a suite of tools for Minecraft
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldGuard team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 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 Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldguard.util.task.progress;
+
+/**
+ * An object that is able to report on its progress.
+ */
+public interface ProgressObservable {
+
+    /**
+     * Get the current percentage of completion.
+     *
+     * @return a progress object
+     */
+    Progress getProgress();
+
+}