From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sat, 17 Jun 2023 11:52:52 +0200
Subject: [PATCH] Folia scheduler and owned region API

Pulling Folia API to Paper is primarily intended for plugins
that want to target both Paper and Folia without unnecessary
compatibility layers.

Add both a location based scheduler, an entity based scheduler,
and a global region scheduler.

Owned region API may be useful for plugins which want to perform
operations over large areas outside of the buffer zone provided
by the regionaliser, as it is not guaranteed that anything
outside of the buffer zone is owned. Then, the plugins may use
the schedulers depending on the result of the ownership check.

diff --git a/src/main/java/io/papermc/paper/plugin/manager/PaperPluginInstanceManager.java b/src/main/java/io/papermc/paper/plugin/manager/PaperPluginInstanceManager.java
index d2dee700f2c5cc7d6a272e751a933901fe7a55b6..834b85f24df023642f8abf7213fe578ac8c17a3e 100644
--- a/src/main/java/io/papermc/paper/plugin/manager/PaperPluginInstanceManager.java
+++ b/src/main/java/io/papermc/paper/plugin/manager/PaperPluginInstanceManager.java
@@ -263,6 +263,22 @@ class PaperPluginInstanceManager {
                 + pluginName + " (Is it up to date?)", ex, plugin); // Paper
         }
 
+        // Paper start - Folia schedulers
+        try {
+            this.server.getGlobalRegionScheduler().cancelTasks(plugin);
+        } catch (Throwable ex) {
+            this.handlePluginException("Error occurred (in the plugin loader) while cancelling global tasks for "
+                + pluginName + " (Is it up to date?)", ex, plugin); // Paper
+        }
+
+        try {
+            this.server.getAsyncScheduler().cancelTasks(plugin);
+        } catch (Throwable ex) {
+            this.handlePluginException("Error occurred (in the plugin loader) while cancelling async tasks for "
+                + pluginName + " (Is it up to date?)", ex, plugin); // Paper
+        }
+        // Paper end - Folia schedulers
+
         try {
             this.server.getServicesManager().unregisterAll(plugin);
         } catch (Throwable ex) {
diff --git a/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java b/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java
new file mode 100644
index 0000000000000000000000000000000000000000..62484ebf4550b05182f693a3180bbac5d5fd906d
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/EntityScheduler.java
@@ -0,0 +1,181 @@
+package io.papermc.paper.threadedregions;
+
+import ca.spottedleaf.concurrentutil.util.Validate;
+import io.papermc.paper.util.TickThread;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import net.minecraft.world.entity.Entity;
+import org.bukkit.craftbukkit.entity.CraftEntity;
+
+import java.util.ArrayDeque;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+
+/**
+ * An entity can move between worlds with an arbitrary tick delay, be temporarily removed
+ * for players (i.e end credits), be partially removed from world state (i.e inactive but not removed),
+ * teleport between ticking regions, teleport between worlds (which will change the underlying Entity object
+ * for non-players), and even be removed entirely from the server. The uncertainty of an entity's state can make
+ * it difficult to schedule tasks without worrying about undefined behaviors resulting from any of the states listed
+ * previously.
+ *
+ * <p>
+ * This class is designed to eliminate those states by providing an interface to run tasks only when an entity
+ * is contained in a world, on the owning thread for the region, and by providing the current Entity object.
+ * The scheduler also allows a task to provide a callback, the "retired" callback, that will be invoked
+ * if the entity is removed before a task that was scheduled could be executed. The scheduler is also
+ * completely thread-safe, allowing tasks to be scheduled from any thread context. The scheduler also indicates
+ * properly whether a task was scheduled successfully (i.e scheduler not retired), thus the code scheduling any task
+ * knows whether the given callbacks will be invoked eventually or not - which may be critical for off-thread
+ * contexts.
+ * </p>
+ */
+public final class EntityScheduler {
+
+    /**
+     * The Entity. Note that it is the CraftEntity, since only that class properly tracks world transfers.
+     */
+    public final CraftEntity entity;
+
+    private static final record ScheduledTask(Consumer<? extends Entity> run, Consumer<? extends Entity> retired) {}
+
+    private long tickCount = 0L;
+    private static final long RETIRED_TICK_COUNT = -1L;
+    private final Object stateLock = new Object();
+    private final Long2ObjectOpenHashMap<List<ScheduledTask>> oneTimeDelayed = new Long2ObjectOpenHashMap<>();
+
+    private final ArrayDeque<ScheduledTask> currentlyExecuting = new ArrayDeque<>();
+
+    public EntityScheduler(final CraftEntity entity) {
+        this.entity = Validate.notNull(entity);
+    }
+
+    /**
+     * Retires the scheduler, preventing new tasks from being scheduled and invoking the retired callback
+     * on all currently scheduled tasks.
+     *
+     * <p>
+     * Note: This should only be invoked after synchronously removing the entity from the world.
+     * </p>
+     *
+     * @throws IllegalStateException If the scheduler is already retired.
+     */
+    public void retire() {
+        synchronized (this.stateLock) {
+            if (this.tickCount == RETIRED_TICK_COUNT) {
+                throw new IllegalStateException("Already retired");
+            }
+            this.tickCount = RETIRED_TICK_COUNT;
+        }
+
+        final Entity thisEntity = this.entity.getHandleRaw();
+
+        // correctly handle and order retiring while running executeTick
+        for (int i = 0, len = this.currentlyExecuting.size(); i < len; ++i) {
+            final ScheduledTask task = this.currentlyExecuting.pollFirst();
+            final Consumer<Entity> retireTask = (Consumer<Entity>)task.retired;
+            if (retireTask == null) {
+                continue;
+            }
+
+            retireTask.accept(thisEntity);
+        }
+
+        for (final List<ScheduledTask> tasks : this.oneTimeDelayed.values()) {
+            for (int i = 0, len = tasks.size(); i < len; ++i) {
+                final ScheduledTask task = tasks.get(i);
+                final Consumer<Entity> retireTask = (Consumer<Entity>)task.retired;
+                if (retireTask == null) {
+                    continue;
+                }
+
+                retireTask.accept(thisEntity);
+            }
+        }
+    }
+
+    /**
+     * Schedules a task with the given delay. If the task failed to schedule because the scheduler is retired (entity
+     * removed), then returns {@code false}. Otherwise, either the run callback will be invoked after the specified delay,
+     * or the retired callback will be invoked if the scheduler is retired.
+     * Note that the retired callback is invoked in critical code, so it should not attempt to remove the entity, remove
+     * other entities, load chunks, load worlds, modify ticket levels, etc.
+     *
+     * <p>
+     * It is guaranteed that the run and retired callback are invoked on the region which owns the entity.
+     * </p>
+     * <p>
+     * The run and retired callback take an Entity parameter representing the current object entity that the scheduler
+     * is tied to. Since the scheduler is transferred when an entity changes dimensions, it is possible the entity parameter
+     * is not the same when the task was first scheduled. Thus, <b>only</b> the parameter provided should be used.
+     * </p>
+     * @param run The callback to run after the specified delay, may not be null.
+     * @param retired Retire callback to run if the entity is retired before the run callback can be invoked, may be null.
+     * @param delay The delay in ticks before the run callback is invoked. Any value less-than 1 is treated as 1.
+     * @return {@code true} if the task was scheduled, which means that either the run function or the retired function
+     *         will be invoked (but never both), or {@code false} indicating neither the run nor retired function will be invoked
+     *         since the scheduler has been retired.
+     */
+    public boolean schedule(final Consumer<? extends Entity> run, final Consumer<? extends Entity> retired, final long delay) {
+        Validate.notNull(run, "Run task may not be null");
+
+        final ScheduledTask task = new ScheduledTask(run, retired);
+        synchronized (this.stateLock) {
+            if (this.tickCount == RETIRED_TICK_COUNT) {
+                return false;
+            }
+            this.oneTimeDelayed.computeIfAbsent(this.tickCount + Math.max(1L, delay), (final long keyInMap) -> {
+                return new ArrayList<>();
+            }).add(task);
+        }
+
+        return true;
+    }
+
+    /**
+     * Executes a tick for the scheduler.
+     *
+     * @throws IllegalStateException If the scheduler is retired.
+     */
+    public void executeTick() {
+        final Entity thisEntity = this.entity.getHandleRaw();
+
+        TickThread.ensureTickThread(thisEntity, "May not tick entity scheduler asynchronously");
+        final List<ScheduledTask> toRun;
+        synchronized (this.stateLock) {
+            if (this.tickCount == RETIRED_TICK_COUNT) {
+                throw new IllegalStateException("Ticking retired scheduler");
+            }
+            ++this.tickCount;
+            if (this.oneTimeDelayed.isEmpty()) {
+                toRun = null;
+            } else {
+                toRun = this.oneTimeDelayed.remove(this.tickCount);
+            }
+        }
+
+        if (toRun != null) {
+            for (int i = 0, len = toRun.size(); i < len; ++i) {
+                this.currentlyExecuting.addLast(toRun.get(i));
+            }
+        }
+
+        // Note: It is allowed for the tasks executed to retire the entity in a given task.
+        for (int i = 0, len = this.currentlyExecuting.size(); i < len; ++i) {
+            if (!TickThread.isTickThreadFor(thisEntity)) {
+                // tp has been queued sync by one of the tasks
+                // in this case, we need to delay the tasks for next tick
+                break;
+            }
+            final ScheduledTask task = this.currentlyExecuting.pollFirst();
+
+            if (this.tickCount != RETIRED_TICK_COUNT) {
+                ((Consumer<Entity>)task.run).accept(thisEntity);
+            } else {
+                // retired synchronously
+                // note: here task is null
+                break;
+            }
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/threadedregions/scheduler/FallbackRegionScheduler.java b/src/main/java/io/papermc/paper/threadedregions/scheduler/FallbackRegionScheduler.java
new file mode 100644
index 0000000000000000000000000000000000000000..94056d61a304ee012ae1828a33412516095f996f
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/scheduler/FallbackRegionScheduler.java
@@ -0,0 +1,30 @@
+package io.papermc.paper.threadedregions.scheduler;
+
+import org.bukkit.World;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.function.Consumer;
+
+public final class FallbackRegionScheduler implements RegionScheduler {
+
+    @Override
+    public void execute(@NotNull final Plugin plugin, @NotNull final World world, final int chunkX, final int chunkZ, @NotNull final Runnable run) {
+        plugin.getServer().getGlobalRegionScheduler().execute(plugin, run);
+    }
+
+    @Override
+    public @NotNull ScheduledTask run(@NotNull final Plugin plugin, @NotNull final World world, final int chunkX, final int chunkZ, @NotNull final Consumer<ScheduledTask> task) {
+        return plugin.getServer().getGlobalRegionScheduler().run(plugin, task);
+    }
+
+    @Override
+    public @NotNull ScheduledTask runDelayed(@NotNull final Plugin plugin, @NotNull final World world, final int chunkX, final int chunkZ, @NotNull final Consumer<ScheduledTask> task, final long delayTicks) {
+        return plugin.getServer().getGlobalRegionScheduler().runDelayed(plugin, task, delayTicks);
+    }
+
+    @Override
+    public @NotNull ScheduledTask runAtFixedRate(@NotNull final Plugin plugin, @NotNull final World world, final int chunkX, final int chunkZ, @NotNull final Consumer<ScheduledTask> task, final long initialDelayTicks, final long periodTicks) {
+        return plugin.getServer().getGlobalRegionScheduler().runAtFixedRate(plugin, task, initialDelayTicks, periodTicks);
+    }
+}
diff --git a/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaAsyncScheduler.java b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaAsyncScheduler.java
new file mode 100644
index 0000000000000000000000000000000000000000..374abffb9f1ce1a308822aed13038e77fe9ca08b
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaAsyncScheduler.java
@@ -0,0 +1,328 @@
+package io.papermc.paper.threadedregions.scheduler;
+
+import ca.spottedleaf.concurrentutil.util.Validate;
+import com.mojang.logging.LogUtils;
+import org.bukkit.plugin.IllegalPluginAccessException;
+import org.bukkit.plugin.Plugin;
+import org.slf4j.Logger;
+
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.Executor;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.SynchronousQueue;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+
+public final class FoliaAsyncScheduler implements AsyncScheduler {
+
+    private static final Logger LOGGER = LogUtils.getClassLogger();
+
+    private final Executor executors = new ThreadPoolExecutor(Math.max(4, Runtime.getRuntime().availableProcessors() / 2), Integer.MAX_VALUE,
+        30L, TimeUnit.SECONDS, new SynchronousQueue<>(),
+        new ThreadFactory() {
+            private final AtomicInteger idGenerator = new AtomicInteger();
+
+            @Override
+            public Thread newThread(final Runnable run) {
+                final Thread ret = new Thread(run);
+
+                ret.setName("Folia Async Scheduler Thread #" + this.idGenerator.getAndIncrement());
+                ret.setPriority(Thread.NORM_PRIORITY - 1);
+                ret.setUncaughtExceptionHandler((final Thread thread, final Throwable thr) -> {
+                    LOGGER.error("Uncaught exception in thread: " + thread.getName(), thr);
+                });
+
+                return ret;
+            }
+        }
+    );
+
+    private final ScheduledExecutorService timerThread = Executors.newSingleThreadScheduledExecutor(new ThreadFactory() {
+        @Override
+        public Thread newThread(final Runnable run) {
+            final Thread ret = new Thread(run);
+
+            ret.setName("Folia Async Scheduler Thread Timer");
+            ret.setPriority(Thread.NORM_PRIORITY + 1);
+            ret.setUncaughtExceptionHandler((final Thread thread, final Throwable thr) -> {
+                LOGGER.error("Uncaught exception in thread: " + thread.getName(), thr);
+            });
+
+            return ret;
+        }
+    });
+
+    private final Set<AsyncScheduledTask> tasks = ConcurrentHashMap.newKeySet();
+
+    @Override
+    public ScheduledTask runNow(final Plugin plugin, final Consumer<ScheduledTask> task) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        final AsyncScheduledTask ret = new AsyncScheduledTask(plugin, -1L, task, null, -1L);
+
+        this.tasks.add(ret);
+        this.executors.execute(ret);
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    @Override
+    public ScheduledTask runDelayed(final Plugin plugin, final Consumer<ScheduledTask> task, final long delay,
+                                    final TimeUnit unit) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        Validate.notNull(unit, "Time unit may not be null");
+        if (delay < 0L) {
+            throw new IllegalArgumentException("Delay may not be < 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        return this.scheduleTimerTask(plugin, task, delay, -1L, unit);
+    }
+
+    @Override
+    public ScheduledTask runAtFixedRate(final Plugin plugin, final Consumer<ScheduledTask> task, final long initialDelay,
+                                        final long period, final TimeUnit unit) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        Validate.notNull(unit, "Time unit may not be null");
+        if (initialDelay < 0L) {
+            throw new IllegalArgumentException("Initial delay may not be < 0");
+        }
+        if (period <= 0L) {
+            throw new IllegalArgumentException("Period may not be <= 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        return this.scheduleTimerTask(plugin, task, initialDelay, period, unit);
+    }
+
+    private AsyncScheduledTask scheduleTimerTask(final Plugin plugin, final Consumer<ScheduledTask> task, final long initialDelay,
+                                                 final long period, final TimeUnit unit) {
+        final AsyncScheduledTask ret = new AsyncScheduledTask(
+            plugin, period <= 0 ? period : unit.toNanos(period), task, null,
+            System.nanoTime() + unit.toNanos(initialDelay)
+        );
+
+        synchronized (ret) {
+            // even though ret is not published, we need to synchronise while scheduling to avoid a race condition
+            // for when a scheduled task immediately executes before we update the delay field and state field
+            ret.setDelay(this.timerThread.schedule(ret, initialDelay, unit));
+            this.tasks.add(ret);
+        }
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    @Override
+    public void cancelTasks(final Plugin plugin) {
+        Validate.notNull(plugin, "Plugin may not be null");
+
+        for (final AsyncScheduledTask task : this.tasks) {
+            if (task.plugin == plugin) {
+                task.cancel();
+            }
+        }
+    }
+
+    private final class AsyncScheduledTask implements ScheduledTask, Runnable {
+
+        private static final int STATE_ON_TIMER            = 0;
+        private static final int STATE_SCHEDULED_EXECUTOR  = 1;
+        private static final int STATE_EXECUTING           = 2;
+        private static final int STATE_EXECUTING_CANCELLED = 3;
+        private static final int STATE_FINISHED            = 4;
+        private static final int STATE_CANCELLED           = 5;
+
+        private final Plugin plugin;
+        private final long repeatDelay; // in ns
+        private Consumer<ScheduledTask> run;
+        private ScheduledFuture<?> delay;
+        private int state;
+        private long scheduleTarget;
+
+        public AsyncScheduledTask(final Plugin plugin, final long repeatDelay, final Consumer<ScheduledTask> run,
+                                  final ScheduledFuture<?> delay, final long firstTarget) {
+            this.plugin = plugin;
+            this.repeatDelay = repeatDelay;
+            this.run = run;
+            this.delay = delay;
+            this.state = delay == null ? STATE_SCHEDULED_EXECUTOR : STATE_ON_TIMER;
+            this.scheduleTarget = firstTarget;
+        }
+
+        private void setDelay(final ScheduledFuture<?> delay) {
+            this.delay = delay;
+            this.state = STATE_SCHEDULED_EXECUTOR;
+        }
+
+        @Override
+        public void run() {
+            final boolean repeating = this.isRepeatingTask();
+            // try to advance state
+            final boolean timer;
+            synchronized (this) {
+                if (this.state == STATE_ON_TIMER) {
+                    timer = true;
+                    this.delay = null;
+                    this.state = STATE_SCHEDULED_EXECUTOR;
+                } else if (this.state != STATE_SCHEDULED_EXECUTOR) {
+                    // cancelled
+                    if (this.state != STATE_CANCELLED) {
+                        throw new IllegalStateException("Wrong state: " + this.state);
+                    }
+                    return;
+                } else {
+                    timer = false;
+                    this.state = STATE_EXECUTING;
+                }
+            }
+
+            if (timer) {
+                // the scheduled executor is single thread, and unfortunately not expandable with threads
+                // so we just schedule onto the executor
+                FoliaAsyncScheduler.this.executors.execute(this);
+                return;
+            }
+
+            try {
+                this.run.accept(this);
+            } catch (final Throwable throwable) {
+                this.plugin.getLogger().log(Level.WARNING, "Async task for " + this.plugin.getDescription().getFullName() + " generated an exception", throwable);
+            } finally {
+                boolean removeFromTasks = false;
+                synchronized (this) {
+                    if (!repeating) {
+                        // only want to execute once, so we're done
+                        removeFromTasks = true;
+                        this.state = STATE_FINISHED;
+                    } else if (this.state != STATE_EXECUTING_CANCELLED) {
+                        this.state = STATE_ON_TIMER;
+                        // account for any delays, whether it be by task exec. or scheduler issues so that we keep
+                        // the fixed schedule
+                        final long currTime = System.nanoTime();
+                        final long delay = Math.max(0L, this.scheduleTarget + this.repeatDelay - currTime);
+                        this.scheduleTarget = currTime + delay;
+                        this.delay = FoliaAsyncScheduler.this.timerThread.schedule(this, delay, TimeUnit.NANOSECONDS);
+                    } else {
+                        // cancelled repeating task
+                        removeFromTasks = true;
+                    }
+                }
+
+                if (removeFromTasks) {
+                    this.run = null;
+                    FoliaAsyncScheduler.this.tasks.remove(this);
+                }
+            }
+        }
+
+        @Override
+        public Plugin getOwningPlugin() {
+            return this.plugin;
+        }
+
+        @Override
+        public boolean isRepeatingTask() {
+            return this.repeatDelay > 0L;
+        }
+
+        @Override
+        public CancelledState cancel() {
+            ScheduledFuture<?> delay = null;
+            CancelledState ret;
+            synchronized (this) {
+                switch (this.state) {
+                    case STATE_ON_TIMER: {
+                        delay = this.delay;
+                        this.delay = null;
+                        this.state = STATE_CANCELLED;
+                        ret = CancelledState.CANCELLED_BY_CALLER;
+                        break;
+                    }
+                    case STATE_SCHEDULED_EXECUTOR: {
+                        this.state = STATE_CANCELLED;
+                        ret = CancelledState.CANCELLED_BY_CALLER;
+                        break;
+                    }
+                    case STATE_EXECUTING: {
+                        if (!this.isRepeatingTask()) {
+                            return CancelledState.RUNNING;
+                        }
+                        this.state = STATE_EXECUTING_CANCELLED;
+                        return CancelledState.NEXT_RUNS_CANCELLED;
+                    }
+                    case STATE_EXECUTING_CANCELLED: {
+                        return CancelledState.NEXT_RUNS_CANCELLED_ALREADY;
+                    }
+                    case STATE_FINISHED: {
+                        return CancelledState.ALREADY_EXECUTED;
+                    }
+                    case STATE_CANCELLED: {
+                        return CancelledState.CANCELLED_ALREADY;
+                    }
+                    default: {
+                        throw new IllegalStateException("Unknown state: " + this.state);
+                    }
+                }
+            }
+
+            if (delay != null) {
+                delay.cancel(false);
+            }
+            this.run = null;
+            FoliaAsyncScheduler.this.tasks.remove(this);
+            return ret;
+        }
+
+        @Override
+        public ExecutionState getExecutionState() {
+            synchronized (this) {
+                switch (this.state) {
+                    case STATE_ON_TIMER:
+                    case STATE_SCHEDULED_EXECUTOR:
+                        return ExecutionState.IDLE;
+                    case STATE_EXECUTING:
+                        return ExecutionState.RUNNING;
+                    case STATE_EXECUTING_CANCELLED:
+                        return ExecutionState.CANCELLED_RUNNING;
+                    case STATE_FINISHED:
+                        return ExecutionState.FINISHED;
+                    case STATE_CANCELLED:
+                        return ExecutionState.CANCELLED;
+                    default: {
+                        throw new IllegalStateException("Unknown state: " + this.state);
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaEntityScheduler.java b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaEntityScheduler.java
new file mode 100644
index 0000000000000000000000000000000000000000..011754962896e32f51ed4606dcbea18a430a2bc1
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaEntityScheduler.java
@@ -0,0 +1,268 @@
+package io.papermc.paper.threadedregions.scheduler;
+
+import ca.spottedleaf.concurrentutil.util.ConcurrentUtil;
+import ca.spottedleaf.concurrentutil.util.Validate;
+import net.minecraft.world.entity.Entity;
+import org.bukkit.craftbukkit.entity.CraftEntity;
+import org.bukkit.plugin.IllegalPluginAccessException;
+import org.bukkit.plugin.Plugin;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.invoke.VarHandle;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+
+public final class FoliaEntityScheduler implements EntityScheduler {
+
+    private final CraftEntity entity;
+
+    public FoliaEntityScheduler(final CraftEntity entity) {
+        this.entity = entity;
+    }
+
+    private static Consumer<? extends Entity> wrap(final Plugin plugin, final Runnable runnable) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(runnable, "Runnable may not be null");
+
+        return (final Entity nmsEntity) -> {
+            if (!plugin.isEnabled()) {
+                // don't execute if the plugin is disabled
+                return;
+            }
+            try {
+                runnable.run();
+            } catch (final Throwable throwable) {
+                plugin.getLogger().log(Level.WARNING, "Entity task for " + plugin.getDescription().getFullName() + " generated an exception", throwable);
+            }
+        };
+    }
+
+    @Override
+    public boolean execute(final Plugin plugin, final Runnable run, final Runnable retired,
+                           final long delay) {
+        final Consumer<? extends Entity> runNMS = wrap(plugin, run);
+        final Consumer<? extends Entity> runRetired = retired == null ? null : wrap(plugin, retired);
+
+        return this.entity.taskScheduler.schedule(runNMS, runRetired, delay);
+    }
+
+    @Override
+    public @Nullable ScheduledTask run(final Plugin plugin, final Consumer<ScheduledTask> task, final Runnable retired) {
+        return this.runDelayed(plugin, task, retired, 1);
+    }
+
+    @Override
+    public @Nullable ScheduledTask runDelayed(final Plugin plugin, final Consumer<ScheduledTask> task, final Runnable retired,
+                                              final long delayTicks) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        if (delayTicks <= 0) {
+            throw new IllegalArgumentException("Delay ticks may not be <= 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        final EntityScheduledTask ret = new EntityScheduledTask(plugin, -1, task, retired);
+
+        if (!this.scheduleInternal(ret, delayTicks)) {
+            return null;
+        }
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    @Override
+    public @Nullable ScheduledTask runAtFixedRate(final Plugin plugin, final Consumer<ScheduledTask> task,
+                                                  final Runnable retired, final long initialDelayTicks, final long periodTicks) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        if (initialDelayTicks <= 0) {
+            throw new IllegalArgumentException("Initial delay ticks may not be <= 0");
+        }
+        if (periodTicks <= 0) {
+            throw new IllegalArgumentException("Period ticks may not be <= 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        final EntityScheduledTask ret = new EntityScheduledTask(plugin, periodTicks, task, retired);
+
+        if (!this.scheduleInternal(ret, initialDelayTicks)) {
+            return null;
+        }
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    private boolean scheduleInternal(final EntityScheduledTask ret, final long delay) {
+        return this.entity.taskScheduler.schedule(ret, ret, delay);
+    }
+
+    private final class EntityScheduledTask implements ScheduledTask, Consumer<Entity> {
+
+        private static final int STATE_IDLE                = 0;
+        private static final int STATE_EXECUTING           = 1;
+        private static final int STATE_EXECUTING_CANCELLED = 2;
+        private static final int STATE_FINISHED            = 3;
+        private static final int STATE_CANCELLED           = 4;
+
+        private final Plugin plugin;
+        private final long repeatDelay; // in ticks
+        private Consumer<ScheduledTask> run;
+        private Runnable retired;
+        private volatile int state;
+
+        private static final VarHandle STATE_HANDLE = ConcurrentUtil.getVarHandle(EntityScheduledTask.class, "state", int.class);
+
+        private EntityScheduledTask(final Plugin plugin, final long repeatDelay, final Consumer<ScheduledTask> run, final Runnable retired) {
+            this.plugin = plugin;
+            this.repeatDelay = repeatDelay;
+            this.run = run;
+            this.retired = retired;
+        }
+
+        private final int getStateVolatile() {
+            return (int)STATE_HANDLE.get(this);
+        }
+
+        private final int compareAndExchangeStateVolatile(final int expect, final int update) {
+            return (int)STATE_HANDLE.compareAndExchange(this, expect, update);
+        }
+
+        private final void setStateVolatile(final int value) {
+            STATE_HANDLE.setVolatile(this, value);
+        }
+
+        @Override
+        public void accept(final Entity entity) {
+            if (!this.plugin.isEnabled()) {
+                // don't execute if the plugin is disabled
+                this.setStateVolatile(STATE_CANCELLED);
+                return;
+            }
+
+            final boolean repeating = this.isRepeatingTask();
+            if (STATE_IDLE != this.compareAndExchangeStateVolatile(STATE_IDLE, STATE_EXECUTING)) {
+                // cancelled
+                return;
+            }
+
+            final boolean retired = entity.isRemoved();
+
+            try {
+                if (!retired) {
+                    this.run.accept(this);
+                } else {
+                    if (this.retired != null) {
+                        this.retired.run();
+                    }
+                }
+            } catch (final Throwable throwable) {
+                this.plugin.getLogger().log(Level.WARNING, "Entity task for " + this.plugin.getDescription().getFullName() + " generated an exception", throwable);
+            } finally {
+                boolean reschedule = false;
+                 if (!repeating && !retired) {
+                    this.setStateVolatile(STATE_FINISHED);
+                } else if (retired || !this.plugin.isEnabled()) {
+                     this.setStateVolatile(STATE_CANCELLED);
+                } else if (STATE_EXECUTING == this.compareAndExchangeStateVolatile(STATE_EXECUTING, STATE_IDLE)) {
+                    reschedule = true;
+                } // else: cancelled repeating task
+
+                if (!reschedule) {
+                    this.run = null;
+                    this.retired = null;
+                } else {
+                    if (!FoliaEntityScheduler.this.scheduleInternal(this, this.repeatDelay)) {
+                        // the task itself must have removed the entity, so in this case we need to mark as cancelled
+                        this.setStateVolatile(STATE_CANCELLED);
+                    }
+                }
+            }
+        }
+
+        @Override
+        public Plugin getOwningPlugin() {
+            return this.plugin;
+        }
+
+        @Override
+        public boolean isRepeatingTask() {
+            return this.repeatDelay > 0;
+        }
+
+        @Override
+        public CancelledState cancel() {
+            for (int curr = this.getStateVolatile();;) {
+                switch (curr) {
+                    case STATE_IDLE: {
+                        if (STATE_IDLE == (curr = this.compareAndExchangeStateVolatile(STATE_IDLE, STATE_CANCELLED))) {
+                            this.state = STATE_CANCELLED;
+                            this.run = null;
+                            this.retired = null;
+                            return CancelledState.CANCELLED_BY_CALLER;
+                        }
+                        // try again
+                        continue;
+                    }
+                    case STATE_EXECUTING: {
+                        if (!this.isRepeatingTask()) {
+                            return CancelledState.RUNNING;
+                        }
+                        if (STATE_EXECUTING == (curr = this.compareAndExchangeStateVolatile(STATE_EXECUTING, STATE_EXECUTING_CANCELLED))) {
+                            return CancelledState.NEXT_RUNS_CANCELLED;
+                        }
+                        // try again
+                        continue;
+                    }
+                    case STATE_EXECUTING_CANCELLED: {
+                        return CancelledState.NEXT_RUNS_CANCELLED_ALREADY;
+                    }
+                    case STATE_FINISHED: {
+                        return CancelledState.ALREADY_EXECUTED;
+                    }
+                    case STATE_CANCELLED: {
+                        return CancelledState.CANCELLED_ALREADY;
+                    }
+                    default: {
+                        throw new IllegalStateException("Unknown state: " + curr);
+                    }
+                }
+            }
+        }
+
+        @Override
+        public ExecutionState getExecutionState() {
+            final int state = this.getStateVolatile();
+            switch (state) {
+                case STATE_IDLE:
+                    return ExecutionState.IDLE;
+                case STATE_EXECUTING:
+                    return ExecutionState.RUNNING;
+                case STATE_EXECUTING_CANCELLED:
+                    return ExecutionState.CANCELLED_RUNNING;
+                case STATE_FINISHED:
+                    return ExecutionState.FINISHED;
+                case STATE_CANCELLED:
+                    return ExecutionState.CANCELLED;
+                default: {
+                    throw new IllegalStateException("Unknown state: " + state);
+                }
+            }
+        }
+    }
+}
diff --git a/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaGlobalRegionScheduler.java b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaGlobalRegionScheduler.java
new file mode 100644
index 0000000000000000000000000000000000000000..d306f911757a4d556c82c0070d4837db87afc497
--- /dev/null
+++ b/src/main/java/io/papermc/paper/threadedregions/scheduler/FoliaGlobalRegionScheduler.java
@@ -0,0 +1,267 @@
+package io.papermc.paper.threadedregions.scheduler;
+
+import ca.spottedleaf.concurrentutil.util.ConcurrentUtil;
+import ca.spottedleaf.concurrentutil.util.Validate;
+import it.unimi.dsi.fastutil.longs.Long2ObjectOpenHashMap;
+import org.bukkit.plugin.IllegalPluginAccessException;
+import org.bukkit.plugin.Plugin;
+
+import java.lang.invoke.VarHandle;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.function.Consumer;
+import java.util.logging.Level;
+
+public class FoliaGlobalRegionScheduler implements GlobalRegionScheduler {
+
+    private long tickCount = 0L;
+    private final Object stateLock = new Object();
+    private final Long2ObjectOpenHashMap<List<GlobalScheduledTask>> tasksByDeadline = new Long2ObjectOpenHashMap<>();
+
+    public void tick() {
+        final List<GlobalScheduledTask> run;
+        synchronized (this.stateLock) {
+            ++this.tickCount;
+            if (this.tasksByDeadline.isEmpty()) {
+                run = null;
+            } else {
+                run = this.tasksByDeadline.remove(this.tickCount);
+            }
+        }
+
+        if (run == null) {
+            return;
+        }
+
+        for (int i = 0, len = run.size(); i < len; ++i) {
+            run.get(i).run();
+        }
+    }
+
+    @Override
+    public void execute(final Plugin plugin, final Runnable run) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(run, "Runnable may not be null");
+
+        this.run(plugin, (final ScheduledTask task) -> {
+            run.run();
+        });
+    }
+
+    @Override
+    public ScheduledTask run(final Plugin plugin, final Consumer<ScheduledTask> task) {
+        return this.runDelayed(plugin, task, 1);
+    }
+
+    @Override
+    public ScheduledTask runDelayed(final Plugin plugin, final Consumer<ScheduledTask> task, final long delayTicks) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        if (delayTicks <= 0) {
+            throw new IllegalArgumentException("Delay ticks may not be <= 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        final GlobalScheduledTask ret = new GlobalScheduledTask(plugin, -1, task);
+
+        this.scheduleInternal(ret, delayTicks);
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    @Override
+    public ScheduledTask runAtFixedRate(final Plugin plugin, final Consumer<ScheduledTask> task, final long initialDelayTicks, final long periodTicks) {
+        Validate.notNull(plugin, "Plugin may not be null");
+        Validate.notNull(task, "Task may not be null");
+        if (initialDelayTicks <= 0) {
+            throw new IllegalArgumentException("Initial delay ticks may not be <= 0");
+        }
+        if (periodTicks <= 0) {
+            throw new IllegalArgumentException("Period ticks may not be <= 0");
+        }
+
+        if (!plugin.isEnabled()) {
+            throw new IllegalPluginAccessException("Plugin attempted to register task while disabled");
+        }
+
+        final GlobalScheduledTask ret = new GlobalScheduledTask(plugin, periodTicks, task);
+
+        this.scheduleInternal(ret, initialDelayTicks);
+
+        if (!plugin.isEnabled()) {
+            // handle race condition where plugin is disabled asynchronously
+            ret.cancel();
+        }
+
+        return ret;
+    }
+
+    @Override
+    public void cancelTasks(final Plugin plugin) {
+        Validate.notNull(plugin, "Plugin may not be null");
+
+        final List<GlobalScheduledTask> toCancel = new ArrayList<>();
+        synchronized (this.stateLock) {
+            for (final List<GlobalScheduledTask> tasks : this.tasksByDeadline.values()) {
+                for (int i = 0, len = tasks.size(); i < len; ++i) {
+                    final GlobalScheduledTask task = tasks.get(i);
+                    if (task.plugin == plugin) {
+                        toCancel.add(task);
+                    }
+                }
+            }
+        }
+
+        for (int i = 0, len = toCancel.size(); i < len; ++i) {
+            toCancel.get(i).cancel();
+        }
+    }
+
+    private void scheduleInternal(final GlobalScheduledTask task, final long delay) {
+        // note: delay > 0
+        synchronized (this.stateLock) {
+            this.tasksByDeadline.computeIfAbsent(this.tickCount + delay, (final long keyInMap) -> {
+                return new ArrayList<>();
+            }).add(task);
+        }
+    }
+
+    private final class GlobalScheduledTask implements ScheduledTask, Runnable {
+
+        private static final int STATE_IDLE                = 0;
+        private static final int STATE_EXECUTING           = 1;
+        private static final int STATE_EXECUTING_CANCELLED = 2;
+        private static final int STATE_FINISHED            = 3;
+        private static final int STATE_CANCELLED           = 4;
+
+        private final Plugin plugin;
+        private final long repeatDelay; // in ticks
+        private Consumer<ScheduledTask> run;
+        private volatile int state;
+
+        private static final VarHandle STATE_HANDLE = ConcurrentUtil.getVarHandle(GlobalScheduledTask.class, "state", int.class);
+
+        private GlobalScheduledTask(final Plugin plugin, final long repeatDelay, final Consumer<ScheduledTask> run) {
+            this.plugin = plugin;
+            this.repeatDelay = repeatDelay;
+            this.run = run;
+        }
+
+        private final int getStateVolatile() {
+            return (int)STATE_HANDLE.get(this);
+        }
+
+        private final int compareAndExchangeStateVolatile(final int expect, final int update) {
+            return (int)STATE_HANDLE.compareAndExchange(this, expect, update);
+        }
+
+        private final void setStateVolatile(final int value) {
+            STATE_HANDLE.setVolatile(this, value);
+        }
+
+        @Override
+        public void run() {
+            final boolean repeating = this.isRepeatingTask();
+            if (STATE_IDLE != this.compareAndExchangeStateVolatile(STATE_IDLE, STATE_EXECUTING)) {
+                // cancelled
+                return;
+            }
+
+            try {
+                this.run.accept(this);
+            } catch (final Throwable throwable) {
+                this.plugin.getLogger().log(Level.WARNING, "Global task for " + this.plugin.getDescription().getFullName() + " generated an exception", throwable);
+            } finally {
+                boolean reschedule = false;
+                if (!repeating) {
+                    this.setStateVolatile(STATE_FINISHED);
+                } else if (STATE_EXECUTING == this.compareAndExchangeStateVolatile(STATE_EXECUTING, STATE_IDLE)) {
+                    reschedule = true;
+                } // else: cancelled repeating task
+
+                if (!reschedule) {
+                    this.run = null;
+                } else {
+                    FoliaGlobalRegionScheduler.this.scheduleInternal(this, this.repeatDelay);
+                }
+            }
+        }
+
+        @Override
+        public Plugin getOwningPlugin() {
+            return this.plugin;
+        }
+
+        @Override
+        public boolean isRepeatingTask() {
+            return this.repeatDelay > 0;
+        }
+
+        @Override
+        public CancelledState cancel() {
+            for (int curr = this.getStateVolatile();;) {
+                switch (curr) {
+                    case STATE_IDLE: {
+                        if (STATE_IDLE == (curr = this.compareAndExchangeStateVolatile(STATE_IDLE, STATE_CANCELLED))) {
+                            this.state = STATE_CANCELLED;
+                            this.run = null;
+                            return CancelledState.CANCELLED_BY_CALLER;
+                        }
+                        // try again
+                        continue;
+                    }
+                    case STATE_EXECUTING: {
+                        if (!this.isRepeatingTask()) {
+                            return CancelledState.RUNNING;
+                        }
+                        if (STATE_EXECUTING == (curr = this.compareAndExchangeStateVolatile(STATE_EXECUTING, STATE_EXECUTING_CANCELLED))) {
+                            return CancelledState.NEXT_RUNS_CANCELLED;
+                        }
+                        // try again
+                        continue;
+                    }
+                    case STATE_EXECUTING_CANCELLED: {
+                        return CancelledState.NEXT_RUNS_CANCELLED_ALREADY;
+                    }
+                    case STATE_FINISHED: {
+                        return CancelledState.ALREADY_EXECUTED;
+                    }
+                    case STATE_CANCELLED: {
+                        return CancelledState.CANCELLED_ALREADY;
+                    }
+                    default: {
+                        throw new IllegalStateException("Unknown state: " + curr);
+                    }
+                }
+            }
+        }
+
+        @Override
+        public ExecutionState getExecutionState() {
+            final int state = this.getStateVolatile();
+            switch (state) {
+                case STATE_IDLE:
+                    return ExecutionState.IDLE;
+                case STATE_EXECUTING:
+                    return ExecutionState.RUNNING;
+                case STATE_EXECUTING_CANCELLED:
+                    return ExecutionState.CANCELLED_RUNNING;
+                case STATE_FINISHED:
+                    return ExecutionState.FINISHED;
+                case STATE_CANCELLED:
+                    return ExecutionState.CANCELLED;
+                default: {
+                    throw new IllegalStateException("Unknown state: " + state);
+                }
+            }
+        }
+    }
+}
diff --git a/src/main/java/net/minecraft/server/MinecraftServer.java b/src/main/java/net/minecraft/server/MinecraftServer.java
index 374c20e530d2abd41674d80c711bd3737c6f6941..cbceb0ddea32781f89a19b1edb258bc23b96ee92 100644
--- a/src/main/java/net/minecraft/server/MinecraftServer.java
+++ b/src/main/java/net/minecraft/server/MinecraftServer.java
@@ -1579,6 +1579,20 @@ public abstract class MinecraftServer extends ReentrantBlockableEventLoop<TickTa
         MinecraftTimings.bukkitSchedulerTimer.startTiming(); // Spigot // Paper
         this.server.getScheduler().mainThreadHeartbeat(this.tickCount); // CraftBukkit
         MinecraftTimings.bukkitSchedulerTimer.stopTiming(); // Spigot // Paper
+        // Paper start - Folia scheduler API
+        ((io.papermc.paper.threadedregions.scheduler.FoliaGlobalRegionScheduler) Bukkit.getGlobalRegionScheduler()).tick();
+        getAllLevels().forEach(level -> {
+            for (final Entity entity : level.getEntities().getAll()) {
+                if (entity.isRemoved()) {
+                    continue;
+                }
+                final org.bukkit.craftbukkit.entity.CraftEntity bukkit = entity.getBukkitEntityRaw();
+                if (bukkit != null) {
+                    bukkit.taskScheduler.executeTick();
+                }
+            }
+        });
+        // Paper end - Folia scheduler API
         io.papermc.paper.adventure.providers.ClickCallbackProviderImpl.CALLBACK_MANAGER.handleQueue(this.tickCount); // Paper
         this.profiler.push("commandFunctions");
         MinecraftTimings.commandFunctionsTimer.startTiming(); // Spigot // Paper
diff --git a/src/main/java/net/minecraft/server/players/PlayerList.java b/src/main/java/net/minecraft/server/players/PlayerList.java
index 2ea29c9491186d7a25ed3eed99ee4a488bcaa272..de96d7df65713f2fa7b8f2dd068856bb5fa45a45 100644
--- a/src/main/java/net/minecraft/server/players/PlayerList.java
+++ b/src/main/java/net/minecraft/server/players/PlayerList.java
@@ -640,6 +640,7 @@ public abstract class PlayerList {
 
         entityplayer.unRide();
         worldserver.removePlayerImmediately(entityplayer, Entity.RemovalReason.UNLOADED_WITH_PLAYER);
+        entityplayer.retireScheduler(); // Paper - Folia schedulers
         entityplayer.getAdvancements().stopListening();
         this.players.remove(entityplayer);
         this.playersByName.remove(entityplayer.getScoreboardName().toLowerCase(java.util.Locale.ROOT)); // Spigot
diff --git a/src/main/java/net/minecraft/world/entity/Entity.java b/src/main/java/net/minecraft/world/entity/Entity.java
index ceafb9a540aa0871516f220c79c7f2c30639f069..30c979591001af9f465a2d3d23766e6f9f7d8892 100644
--- a/src/main/java/net/minecraft/world/entity/Entity.java
+++ b/src/main/java/net/minecraft/world/entity/Entity.java
@@ -255,11 +255,23 @@ public abstract class Entity implements SyncedDataHolder, Nameable, EntityAccess
     public @org.jetbrains.annotations.Nullable net.minecraft.server.level.ChunkMap.TrackedEntity tracker; // Paper
     public CraftEntity getBukkitEntity() {
         if (this.bukkitEntity == null) {
-            this.bukkitEntity = CraftEntity.getEntity(this.level.getCraftServer(), this);
+            // Paper start - Folia schedulers
+            synchronized (this) {
+                if (this.bukkitEntity == null) {
+                    return this.bukkitEntity = CraftEntity.getEntity(this.level.getCraftServer(), this);
+                }
+            }
+            // Paper end - Folia schedulers
         }
         return this.bukkitEntity;
     }
 
+    // Paper start
+    public CraftEntity getBukkitEntityRaw() {
+        return this.bukkitEntity;
+    }
+    // Paper end
+
     @Override
     public CommandSender getBukkitSender(CommandSourceStack wrapper) {
         return this.getBukkitEntity();
@@ -4485,6 +4497,7 @@ public abstract class Entity implements SyncedDataHolder, Nameable, EntityAccess
     public final void setRemoved(Entity.RemovalReason entity_removalreason, EntityRemoveEvent.Cause cause) {
         CraftEventFactory.callEntityRemoveEvent(this, cause);
         // CraftBukkit end
+        final boolean alreadyRemoved = this.removalReason != null; // Paper - Folia schedulers
         if (this.removalReason == null) {
             this.removalReason = entity_removalreason;
         }
@@ -4495,12 +4508,28 @@ public abstract class Entity implements SyncedDataHolder, Nameable, EntityAccess
 
         this.getPassengers().forEach(Entity::stopRiding);
         this.levelCallback.onRemove(entity_removalreason);
+        // Paper start - Folia schedulers
+        if (!(this instanceof ServerPlayer) && entity_removalreason != RemovalReason.CHANGED_DIMENSION && !alreadyRemoved) {
+            // Players need to be special cased, because they are regularly removed from the world
+            this.retireScheduler();
+        }
+        // Paper end - Folia schedulers
     }
 
     public void unsetRemoved() {
         this.removalReason = null;
     }
 
+    // Paper start - Folia schedulers
+    /**
+     * Invoked only when the entity is truly removed from the server, never to be added to any world.
+     */
+    public final void retireScheduler() {
+        // we need to force create the bukkit entity so that the scheduler can be retired...
+        this.getBukkitEntity().taskScheduler.retire();
+    }
+    // Paper end - Folia schedulers
+
     @Override
     public void setLevelCallback(EntityInLevelCallback changeListener) {
         this.levelCallback = changeListener;
diff --git a/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 7197cbf15ff9382cbc59c4a58e2f189c8cacbaaa..24097256203990a818aab2716fdb8a4a672a1daa 100644
--- a/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -310,6 +310,76 @@ public final class CraftServer implements Server {
     private final io.papermc.paper.logging.SysoutCatcher sysoutCatcher = new io.papermc.paper.logging.SysoutCatcher(); // Paper
     private final io.papermc.paper.potion.PaperPotionBrewer potionBrewer; // Paper - Custom Potion Mixes
 
+    // Paper start - Folia region threading API
+    private final io.papermc.paper.threadedregions.scheduler.FallbackRegionScheduler regionizedScheduler = new io.papermc.paper.threadedregions.scheduler.FallbackRegionScheduler();
+    private final io.papermc.paper.threadedregions.scheduler.FoliaAsyncScheduler asyncScheduler = new io.papermc.paper.threadedregions.scheduler.FoliaAsyncScheduler();
+    private final io.papermc.paper.threadedregions.scheduler.FoliaGlobalRegionScheduler globalRegionScheduler = new io.papermc.paper.threadedregions.scheduler.FoliaGlobalRegionScheduler();
+
+    @Override
+    public final io.papermc.paper.threadedregions.scheduler.RegionScheduler getRegionScheduler() {
+        return this.regionizedScheduler;
+    }
+
+    @Override
+    public final io.papermc.paper.threadedregions.scheduler.AsyncScheduler getAsyncScheduler() {
+        return this.asyncScheduler;
+    }
+
+    @Override
+    public final io.papermc.paper.threadedregions.scheduler.FoliaGlobalRegionScheduler getGlobalRegionScheduler() {
+        return this.globalRegionScheduler;
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(World world, io.papermc.paper.math.Position position) {
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), position.blockX() >> 4, position.blockZ() >> 4
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(World world, io.papermc.paper.math.Position position, int squareRadiusChunks) {
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), position.blockX() >> 4, position.blockZ() >> 4, squareRadiusChunks
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(Location location) {
+        World world = location.getWorld();
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), location.getBlockX() >> 4, location.getBlockZ() >> 4
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(Location location, int squareRadiusChunks) {
+        World world = location.getWorld();
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), location.getBlockX() >> 4, location.getBlockZ() >> 4, squareRadiusChunks
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(World world, int chunkX, int chunkZ) {
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), chunkX, chunkZ
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(World world, int chunkX, int chunkZ, int squareRadiusChunks) {
+        return io.papermc.paper.util.TickThread.isTickThreadFor(
+            ((CraftWorld) world).getHandle(), chunkX, chunkZ, squareRadiusChunks
+        );
+    }
+
+    @Override
+    public final boolean isOwnedByCurrentRegion(Entity entity) {
+        return io.papermc.paper.util.TickThread.isTickThreadFor(((org.bukkit.craftbukkit.entity.CraftEntity) entity).getHandleRaw());
+    }
+    // Paper end - Folia reagion threading API
+
     static {
         ConfigurationSerialization.registerClass(CraftOfflinePlayer.class);
         ConfigurationSerialization.registerClass(CraftPlayerProfile.class);
diff --git a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
index d8b1cdc78eb234023a42d740599009737201e70e..bc37a3fc38e1966af3722ed16b3f940c2a8387a9 100644
--- a/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
+++ b/src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java
@@ -70,6 +70,15 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
     private EntityDamageEvent lastDamageEvent;
     private final CraftPersistentDataContainer persistentDataContainer = new CraftPersistentDataContainer(CraftEntity.DATA_TYPE_REGISTRY);
     protected net.kyori.adventure.pointer.Pointers adventure$pointers; // Paper - implement pointers
+    // Paper start - Folia shedulers
+    public final io.papermc.paper.threadedregions.EntityScheduler taskScheduler = new io.papermc.paper.threadedregions.EntityScheduler(this);
+    private final io.papermc.paper.threadedregions.scheduler.FoliaEntityScheduler apiScheduler = new io.papermc.paper.threadedregions.scheduler.FoliaEntityScheduler(this);
+
+    @Override
+    public final io.papermc.paper.threadedregions.scheduler.EntityScheduler getScheduler() {
+        return this.apiScheduler;
+    };
+    // Paper end - Folia schedulers
 
     public CraftEntity(final CraftServer server, final Entity entity) {
         this.server = server;
@@ -486,6 +495,12 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
         return this.entity;
     }
 
+    // Paper start
+    public Entity getHandleRaw() {
+        return this.entity;
+    }
+    // Paper end
+
     @Override
     public final EntityType getType() {
         return this.entityType;
