Paper/src/main/java/org/bukkit/craftbukkit/scheduler/CraftScheduler.java

package org.bukkit.craftbukkit.scheduler;

import java.util.LinkedList;
import java.util.TreeMap;
import java.util.Iterator;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.Callable;
import java.util.concurrent.Future;

import org.bukkit.scheduler.BukkitScheduler;
import org.bukkit.plugin.Plugin;

import org.bukkit.craftbukkit.CraftServer;
import org.bukkit.craftbukkit.scheduler.CraftTask;

public class CraftScheduler implements BukkitScheduler, Runnable {

    private final CraftServer server;

    private final CraftThreadManager craftThreadManager = new CraftThreadManager();

    private final LinkedList<Runnable> mainThreadQueue = new LinkedList<Runnable>();
    private final LinkedList<Runnable> syncedTasks = new LinkedList<Runnable>();

    private final TreeMap<CraftTask,Boolean> schedulerQueue = new TreeMap<CraftTask,Boolean>();

    private final Object currentTickSync = new Object();
    private Long currentTick = 0L;

    // This lock locks the mainThreadQueue and the currentTick value
    private final Lock mainThreadLock = new ReentrantLock();

    public void run() {

        while (true) {
            boolean stop = false;
            long firstTick = -1;
            long currentTick = -1;
            CraftTask first = null;
            do {
                synchronized (schedulerQueue) {
                    first = null;
                    if (!schedulerQueue.isEmpty()) {
                        first = schedulerQueue.firstKey();
                        if (first!=null) {
                            currentTick = getCurrentTick();

                            firstTick = first.getExecutionTick();

                            if (currentTick >= firstTick ) {
                                schedulerQueue.remove(first);
                                processTask(first);
                                if (first.getPeriod()>=0) {
                                    first.updateExecution();
                                    schedulerQueue.put(first, first.isSync());
                                }
                            } else {
                                stop = true;
                            }
                        } else {
                            stop = true;
                        }
                    } else {
                        stop = true;
                    }
                }
            } while (!stop);

            long sleepTime = 0;
            if (first == null) {
                sleepTime = 60000L;
            } else {
                currentTick = getCurrentTick();
                sleepTime = (firstTick-currentTick)*50 + 25;
            }

            if (sleepTime < 50L) {
                sleepTime = 50L;
            } else if (sleepTime > 60000L) {
                sleepTime = 60000L;
            }

            synchronized (schedulerQueue) {
                try {
                    schedulerQueue.wait(sleepTime);
                } catch (InterruptedException ie) {
                }
            }
        }
    }

    void processTask(CraftTask task) {
        if (task.isSync()) {
            addToMainThreadQueue(task.getTask());
        } else {
            craftThreadManager.executeTask(task.getTask(), task.getOwner(), task.getIdNumber());
        }
    }

    public CraftScheduler(CraftServer server) {
        this.server = server;

        Thread t = new Thread(this);
        t.start();

    }

    // If the main thread cannot obtain the lock, it doesn't wait
    public void mainThreadHeartbeat(long currentTick) {
        if (mainThreadLock.tryLock()) {
            try {
                this.currentTick = currentTick;
                while (!mainThreadQueue.isEmpty()) {
                    syncedTasks.addLast(mainThreadQueue.removeFirst());
                }
            } finally {
                mainThreadLock.unlock();
            }
            while(!syncedTasks.isEmpty()) {
                syncedTasks.removeFirst().run();
            }
        }
    }

    long getCurrentTick() {
        mainThreadLock.lock();
        long tempTick = 0;
        try {
            tempTick = currentTick;
        } finally {
            mainThreadLock.unlock();
        }
        return tempTick;
    }

    void addToMainThreadQueue(Runnable task) {
        mainThreadLock.lock();
        try {
            mainThreadQueue.addLast(task);
        } finally {
            mainThreadLock.unlock();
        }
    }

    public int scheduleSyncDelayedTask(Plugin plugin, Runnable task, long delay) {
        return scheduleSyncRepeatingTask(plugin, task, delay, -1);
    }

    public int scheduleSyncDelayedTask(Plugin plugin, Runnable task) {
        return scheduleSyncDelayedTask(plugin, task, 0L);
    }

    public int scheduleSyncRepeatingTask(Plugin plugin, Runnable task, long delay, long period) {
        CraftTask newTask = new CraftTask(plugin, task, true, getCurrentTick()+delay, period);
        synchronized (schedulerQueue) {
            schedulerQueue.put(newTask, true);
            schedulerQueue.notify();
        }
        return newTask.getIdNumber();
    }

    public int scheduleAsyncDelayedTask(Plugin plugin, Runnable task, long delay) {
        return scheduleAsyncRepeatingTask(plugin, task, delay, -1);
    }

    public int scheduleAsyncDelayedTask(Plugin plugin, Runnable task) {
        return scheduleAsyncDelayedTask(plugin, task, 0L);
    }

    public int scheduleAsyncRepeatingTask(Plugin plugin, Runnable task, long delay, long period) {
        CraftTask newTask = new CraftTask(plugin, task, false, getCurrentTick()+delay, period);
        synchronized (schedulerQueue) {
            schedulerQueue.put(newTask, false);
            schedulerQueue.notify();
        }
        return newTask.getIdNumber();
    }

    public <T> Future<T> callSyncMethod(Plugin plugin, Callable<T> task) {
        CraftFuture<T> craftFuture = new CraftFuture<T>(this, task);
        synchronized(craftFuture) {
            int taskId = scheduleSyncDelayedTask(plugin, craftFuture);
            craftFuture.setTaskId(taskId);
        }
        return craftFuture;
    }

    public void cancelTask(int taskId) {
        synchronized (schedulerQueue) {
            Iterator<CraftTask> itr = schedulerQueue.keySet().iterator();
            while (itr.hasNext()) {
                CraftTask current = itr.next();
                if (current.getIdNumber() == taskId) {
                    itr.remove();
                }
            }
        }
        craftThreadManager.interruptTask(taskId);
    }

    public void cancelTasks(Plugin plugin) {
        synchronized (schedulerQueue) {
            Iterator<CraftTask> itr = schedulerQueue.keySet().iterator();
            while (itr.hasNext()) {
                CraftTask current = itr.next();
                if (current.getOwner().equals(plugin)) {
                    itr.remove();
                }
            }
        }
        craftThreadManager.interruptTasks(plugin);
    }

    public void cancelAllTasks() {
        synchronized (schedulerQueue) {
            schedulerQueue.clear();
        }
        craftThreadManager.interruptAllTasks();
    }

    public boolean isCurrentlyRunning(int taskId){
        return craftThreadManager.isAlive(taskId);
    }

    public boolean isQueued(int taskId) {
        synchronized (schedulerQueue) {
            Iterator<CraftTask> itr = schedulerQueue.keySet().iterator();
            while (itr.hasNext()) {
                CraftTask current = itr.next();
                if (current.getIdNumber() == taskId) {
                    return true;
                }
            }
            return false;
        }
    }

}