Merge pull request #153 from SquidDev-CC/feature/main-thread-limits

src/main/java/dan200/computercraft/ComputerCraft.java

@@ -24,6 +24,7 @@
 import dan200.computercraft.core.apis.AddressPredicate;
 import dan200.computercraft.core.apis.ApiFactories;
 import dan200.computercraft.core.apis.http.websocket.Websocket;
+import dan200.computercraft.core.computer.MainThread;
 import dan200.computercraft.core.filesystem.ComboMount;
 import dan200.computercraft.core.filesystem.FileMount;
 import dan200.computercraft.core.filesystem.JarMount;
@@ -95,6 +96,7 @@
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.List;
+import java.util.concurrent.TimeUnit;
 import java.util.zip.ZipEntry;
 import java.util.zip.ZipFile;
 
@@ -133,9 +135,12 @@ public class ComputerCraft
     public static boolean disable_lua51_features = false;
     public static String default_computer_settings = "";
     public static boolean debug_enable = true;
-    public static int computer_threads = 1;
     public static boolean logPeripheralErrors = false;
 
+    public static int computer_threads = 1;
+    public static long maxMainGlobalTime = TimeUnit.MILLISECONDS.toNanos( 10 );
+    public static long maxMainComputerTime = TimeUnit.MILLISECONDS.toNanos( 5 );
+
     public static boolean http_enable = true;
     public static boolean http_websocket_enable = true;
     public static AddressPredicate http_whitelist = new AddressPredicate( DEFAULT_HTTP_WHITELIST );
@@ -304,6 +309,7 @@ public void onServerStart( FMLServerStartedEvent event )
         {
             ComputerCraft.serverComputerRegistry.reset();
             WirelessNetwork.resetNetworks();
+            MainThread.reset();
             Tracking.reset();
         }
     }
@@ -315,6 +321,7 @@ public void onServerStopped( FMLServerStoppedEvent event )
         {
             ComputerCraft.serverComputerRegistry.reset();
             WirelessNetwork.resetNetworks();
+            MainThread.reset();
             Tracking.reset();
         }
     }

src/main/java/dan200/computercraft/api/peripheral/IComputerAccess.java

@@ -9,6 +9,8 @@
 import dan200.computercraft.api.ComputerCraftAPI;
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
+import dan200.computercraft.api.lua.ILuaContext;
+import dan200.computercraft.api.lua.ILuaTask;
 import net.minecraft.world.World;
 
 import javax.annotation.Nonnull;
@@ -179,7 +181,7 @@ default Map<String, IPeripheral> getAvailablePeripherals()
     }
 
     /**
-     * Get a reachable peripheral with the given attachement name. This is a equivalent to
+     * Get a reachable peripheral with the given attachment name. This is a equivalent to
      * {@link #getAvailablePeripherals()}{@code .get(name)}, though may be more performant.
      *
      * @param name The peripheral's attached name
@@ -191,4 +193,23 @@ default IPeripheral getAvailablePeripheral( @Nonnull String name )
     {
         return null;
     }
+
+    /**
+     * Get a {@link IWorkMonitor} for tasks your peripheral might execute on the main (server) thread.
+     *
+     * This should be used to ensure your peripheral integrates with ComputerCraft's monitoring and limiting of how much
+     * server time each computer consumes. You should not need to use this if you use
+     * {@link ILuaContext#issueMainThreadTask(ILuaTask)} - this is intended for mods with their own system for running
+     * work on the main thread.
+     *
+     * Please note that the returned implementation is <em>not</em> thread-safe, and should only be used from the main
+     * thread.
+     *
+     * @return The work monitor for the main thread, or {@code null} if this computer does not have one.
+     */
+    @Nullable
+    default IWorkMonitor getMainThreadMonitor()
+    {
+        return null;
+    }
 }

src/main/java/dan200/computercraft/api/peripheral/IWorkMonitor.java

@@ -0,0 +1,79 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.api.peripheral;
+
+import javax.annotation.Nonnull;
+import java.util.Objects;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Monitors "work" associated with a computer, keeping track of how much a computer has done, and ensuring every
+ * computer receives a fair share of any processing time.
+ *
+ * This is primarily intended for work done by peripherals on the main thread (such as on a tile entity's tick), but
+ * could be used for other purposes (such as complex computations done on another thread).
+ *
+ * Before running a task, one should call {@link #canWork()} to determine if the computer is currently allowed to
+ * execute work. If that returns true, you should execute the task and use {@link #trackWork(long, TimeUnit)} to inform
+ * the monitor how long that task took.
+ *
+ * Alternatively, use {@link #runWork(Runnable)} to run and keep track of work.
+ *
+ * @see IComputerAccess#getMainThreadMonitor()
+ */
+public interface IWorkMonitor
+{
+    /**
+     * If the owning computer is currently allowed to execute work.
+     *
+     * @return If we can execute work right now.
+     */
+    boolean canWork();
+
+    /**
+     * If the owning computer is currently allowed to execute work, and has ample time to do so.
+     *
+     * This is effectively a more restrictive form of {@link #canWork()}. One should use that in order to determine if
+     * you may do an initial piece of work, and {@link #shouldWork()} to determine if any additional task may be
+     * performed.
+     *
+     * @return If we should execute work right now.
+     */
+    boolean shouldWork();
+
+    /**
+     * Inform the monitor how long some piece of work took to execute.
+     *
+     * @param time The time some task took to run
+     * @param unit The unit that {@code time} was measured in.
+     */
+    void trackWork( long time, @Nonnull TimeUnit unit );
+
+    /**
+     * Run a task if possible, and inform the monitor of how long it took.
+     *
+     * @param runnable The task to run.
+     * @return If the task was actually run (namely, {@link #canWork()} returned {@code true}).
+     */
+    default boolean runWork( @Nonnull Runnable runnable )
+    {
+        Objects.requireNonNull( runnable, "runnable should not be null" );
+        if( !canWork() ) return false;
+
+        long start = System.nanoTime();
+        try
+        {
+            runnable.run();
+        }
+        finally
+        {
+            trackWork( System.nanoTime() - start, TimeUnit.NANOSECONDS );
+        }
+
+        return true;
+    }
+}

src/main/java/dan200/computercraft/core/apis/ComputerAccess.java

@@ -10,8 +10,7 @@
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
 import dan200.computercraft.api.peripheral.IComputerAccess;
-import dan200.computercraft.core.computer.Computer;
-import dan200.computercraft.core.computer.IComputerOwned;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
 import dan200.computercraft.core.filesystem.FileSystem;
 import dan200.computercraft.core.filesystem.FileSystemException;
 
@@ -21,7 +20,7 @@
 import java.util.Objects;
 import java.util.Set;
 
-public abstract class ComputerAccess implements IComputerAccess, IComputerOwned
+public abstract class ComputerAccess implements IComputerAccess
 {
     private final IAPIEnvironment m_environment;
     private final Set<String> m_mounts = new HashSet<>();
@@ -128,9 +127,9 @@ public void queueEvent( @Nonnull final String event, final Object[] arguments )
 
     @Nullable
     @Override
-    public Computer getComputer()
+    public IWorkMonitor getMainThreadMonitor()
     {
-        return m_environment.getComputer();
+        return m_environment.getMainThreadMonitor();
     }
 
     private String findFreeLocation( String desiredLoc )

src/main/java/dan200/computercraft/core/apis/IAPIEnvironment.java

@@ -7,9 +7,8 @@
 package dan200.computercraft.core.apis;
 
 import dan200.computercraft.api.peripheral.IPeripheral;
-import dan200.computercraft.core.computer.Computer;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
 import dan200.computercraft.core.computer.IComputerEnvironment;
-import dan200.computercraft.core.computer.IComputerOwned;
 import dan200.computercraft.core.filesystem.FileSystem;
 import dan200.computercraft.core.terminal.Terminal;
 import dan200.computercraft.core.tracking.TrackingField;
@@ -17,7 +16,7 @@
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
-public interface IAPIEnvironment extends IComputerOwned
+public interface IAPIEnvironment
 {
     String[] SIDE_NAMES = new String[] {
         "bottom", "top", "back", "front", "right", "left",
@@ -30,15 +29,14 @@ interface IPeripheralChangeListener
         void onPeripheralChanged( int side, @Nullable IPeripheral newPeripheral );
     }
 
-    @Nonnull
-    @Override
-    Computer getComputer();
-
     int getComputerID();
 
     @Nonnull
     IComputerEnvironment getComputerEnvironment();
 
+    @Nonnull
+    IWorkMonitor getMainThreadMonitor();
+
     @Nonnull
     Terminal getTerminal();
 

src/main/java/dan200/computercraft/core/computer/Computer.java

@@ -9,6 +9,7 @@
 import com.google.common.base.Objects;
 import dan200.computercraft.api.lua.ILuaAPI;
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
 import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.filesystem.FileSystem;
 import dan200.computercraft.core.terminal.Terminal;
@@ -25,6 +26,7 @@
  * <li>Keeps track of whether the computer is on and blinking.</li>
  * <li>Monitors whether the computer's visible state (redstone, on/off/blinking) has changed.</li>
  * <li>Passes commands and events to the {@link ComputerExecutor}.</li>
+ * <li>Passes main thread tasks to the {@link MainThreadExecutor}.</li>
  * </ul>
  */
 public class Computer
@@ -39,6 +41,7 @@ public class Computer
     private final IComputerEnvironment m_environment;
     private final Terminal m_terminal;
     private final ComputerExecutor executor;
+    private final MainThreadExecutor serverExecutor;
 
     // Additional state about the computer and its environment.
     private boolean m_blinking = false;
@@ -55,6 +58,7 @@ public Computer( IComputerEnvironment environment, Terminal terminal, int id )
         m_terminal = terminal;
 
         executor = new ComputerExecutor( this );
+        serverExecutor = new MainThreadExecutor( this );
     }
 
     IComputerEnvironment getComputerEnvironment()
@@ -112,6 +116,22 @@ public void queueEvent( String event, Object[] args )
         executor.queueEvent( event, args );
     }
 
+    /**
+     * Queue a task to be run on the main thread, using {@link MainThread}.
+     *
+     * @param runnable The task to run
+     * @return If the task was successfully queued (namely, whether there is space on it).
+     */
+    public boolean queueMainThread( Runnable runnable )
+    {
+        return serverExecutor.enqueue( runnable );
+    }
+
+    public IWorkMonitor getMainThreadMonitor()
+    {
+        return serverExecutor;
+    }
+
     public int getID()
     {
         return m_id;

src/main/java/dan200/computercraft/core/computer/ComputerExecutor.java

@@ -133,7 +133,7 @@ final class ComputerExecutor
      *
      * Note, this should be empty if this computer is off - it is cleared on shutdown and when turning on again.
      */
-    private final Queue<Event> eventQueue = new ArrayDeque<>();
+    private final Queue<Event> eventQueue = new ArrayDeque<>( 4 );
 
     /**
      * Whether we interrupted an event and so should resume it instead of executing another task.

src/main/java/dan200/computercraft/core/computer/ComputerThread.java

@@ -112,7 +112,7 @@ public class ComputerThread
 
         long at = a.virtualRuntime, bt = b.virtualRuntime;
         if( at == bt ) return Integer.compare( a.hashCode(), b.hashCode() );
-        return Long.compare( at, bt );
+        return at < bt ? -1 : 1;
     } );
 
     /**

src/main/java/dan200/computercraft/core/computer/Environment.java

@@ -7,6 +7,7 @@
 package dan200.computercraft.core.computer;
 
 import dan200.computercraft.api.peripheral.IPeripheral;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
 import dan200.computercraft.core.apis.IAPIEnvironment;
 import dan200.computercraft.core.filesystem.FileSystem;
 import dan200.computercraft.core.terminal.Terminal;
@@ -58,13 +59,6 @@ public final class Environment implements IAPIEnvironment
         this.computer = computer;
     }
 
-    @Nonnull
-    @Override
-    public Computer getComputer()
-    {
-        return computer;
-    }
-
     @Override
     public int getComputerID()
     {
@@ -78,6 +72,13 @@ public IComputerEnvironment getComputerEnvironment()
         return computer.getComputerEnvironment();
     }
 
+    @Nonnull
+    @Override
+    public IWorkMonitor getMainThreadMonitor()
+    {
+        return computer.getMainThreadMonitor();
+    }
+
     @Nonnull
     @Override
     public Terminal getTerminal()

src/main/java/dan200/computercraft/core/computer/IComputerOwned.java

@@ -1,33 +0,0 @@
-/*
- * This file is part of ComputerCraft - http://www.computercraft.info
- * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
- * Send enquiries to dratcliffe@gmail.com
- */
-
-package dan200.computercraft.core.computer;
-
-import dan200.computercraft.api.peripheral.IComputerAccess;
-
-import javax.annotation.Nullable;
-
-/**
- * {@link IComputerOwned} marks objects which are known to belong to a computer.
- *
- * The primary purpose of this is to allow Plethora (and potentially other mods) to run the various tracking methods
- * on {@link Computer}.
- *
- * You can generally assume {@link IComputerAccess} implements this interface, though you should always check first.
- *
- * @see dan200.computercraft.core.apis.ComputerAccess
- * @see dan200.computercraft.shared.peripheral.modem.wired.WiredModemPeripheral and the peripheral wrapper
- */
-public interface IComputerOwned
-{
-    /**
-     * Get the computer associated with this object
-     *
-     * @return The associated object, or {@code null} if none is known.
-     */
-    @Nullable
-    Computer getComputer();
-}

src/main/java/dan200/computercraft/core/computer/ITask.java

@@ -1,17 +0,0 @@
-/*
- * This file is part of ComputerCraft - http://www.computercraft.info
- * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
- * Send enquiries to dratcliffe@gmail.com
- */
-
-package dan200.computercraft.core.computer;
-
-import javax.annotation.Nonnull;
-
-public interface ITask
-{
-    @Nonnull
-    Computer getOwner();
-
-    void execute();
-}

src/main/java/dan200/computercraft/core/computer/MainThread.java

@@ -6,66 +6,189 @@
 
 package dan200.computercraft.core.computer;
 
-import dan200.computercraft.core.tracking.Tracking;
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.lua.ILuaTask;
 
-import java.util.ArrayDeque;
-import java.util.Queue;
+import javax.annotation.Nonnull;
+import java.util.HashSet;
+import java.util.TreeSet;
+import java.util.concurrent.atomic.AtomicLong;
 
+/**
+ * Runs tasks on the main (server) thread, ticks {@link MainThreadExecutor}s, and limits how much time is used this
+ * tick.
+ *
+ * Similar to {@link MainThreadExecutor}, the {@link MainThread} can be in one of three states: cool, hot and cooling.
+ * However, the implementation here is a little different:
+ *
+ * {@link MainThread} starts cool, and runs as many tasks as it can in the current {@link #budget}ns. Any external tasks
+ * (those run by tile entities, etc...) will also consume the budget
+ *
+ * Next tick, we put {@link ComputerCraft#maxMainGlobalTime} into our budget (and clamp it to that value to). If we're
+ * still over budget, then we should not execute <em>any</em> work (either as part of {@link MainThread} or externally).
+ */
 public class MainThread
 {
-    private static final int MAX_TASKS_PER_TICK = 1000;
-    private static final int MAX_TASKS_TOTAL = 50000;
+    /**
+     * An internal counter for {@link ILuaTask} ids.
+     *
+     * @see dan200.computercraft.api.lua.ILuaContext#issueMainThreadTask(ILuaTask)
+     * @see #getUniqueTaskID()
+     */
+    private static final AtomicLong lastTaskId = new AtomicLong();
 
-    private static final Queue<ITask> m_outstandingTasks = new ArrayDeque<>();
-    private static final Object m_nextUnusedTaskIDLock = new Object();
-    private static long m_nextUnusedTaskID = 0;
+    /**
+     * The queue of {@link MainThreadExecutor}s with tasks to perform.
+     */
+    private static final TreeSet<MainThreadExecutor> executors = new TreeSet<>( ( a, b ) -> {
+        if( a == b ) return 0; // Should never happen, but let's be consistent here
+
+        long at = a.virtualTime, bt = b.virtualTime;
+        if( at == bt ) return Integer.compare( a.hashCode(), b.hashCode() );
+        return at < bt ? -1 : 1;
+    } );
+    ;
+
+    /**
+     * The set of executors which went over budget in a previous tick, and are waiting for their time to run down.
+     *
+     * @see MainThreadExecutor#tickCooling()
+     * @see #cooling(MainThreadExecutor)
+     */
+    private static final HashSet<MainThreadExecutor> cooling = new HashSet<>();
+
+    /**
+     * The current tick number. This is used by {@link MainThreadExecutor} to determine when to reset its own time
+     * counter.
+     *
+     * @see #currentTick()
+     */
+    private static int currentTick;
+
+    /**
+     * The remaining budgeted time for this tick. This may be negative, in the case that we've gone over budget.
+     */
+    private static long budget;
+
+    /**
+     * Whether we should be executing any work this tick.
+     *
+     * This is true iff {@code MAX_TICK_TIME - currentTime} was true <em>at the beginning of the tick</em>.
+     */
+    private static boolean canExecute = true;
+
+    private static long minimumTime = 0;
 
     public static long getUniqueTaskID()
     {
-        synchronized( m_nextUnusedTaskIDLock )
+        return lastTaskId.incrementAndGet();
+    }
+
+    static void queue( @Nonnull MainThreadExecutor executor, boolean sleeper )
+    {
+        synchronized( executors )
         {
-            return ++m_nextUnusedTaskID;
+            if( executor.onQueue ) throw new IllegalStateException( "Cannot queue already queued executor" );
+            executor.onQueue = true;
+            executor.updateTime();
+
+            // We're not currently on the queue, so update its current execution time to
+            // ensure its at least as high as the minimum.
+            long newRuntime = minimumTime;
+
+            // Slow down new computers a little bit.
+            if( executor.virtualTime == 0 ) newRuntime += ComputerCraft.maxMainComputerTime;
+
+            executor.virtualTime = Math.max( newRuntime, executor.virtualTime );
+
+            executors.add( executor );
         }
     }
 
-    public static boolean queueTask( ITask task )
+    static void cooling( @Nonnull MainThreadExecutor executor )
     {
-        synchronized( m_outstandingTasks )
-        {
-            if( m_outstandingTasks.size() < MAX_TASKS_TOTAL )
-            {
-                m_outstandingTasks.offer( task );
-                return true;
-            }
-        }
-        return false;
+        cooling.add( executor );
+    }
+
+    static void consumeTime( long time )
+    {
+        budget -= time;
+    }
+
+    static boolean canExecute()
+    {
+        return canExecute;
+    }
+
+    static int currentTick()
+    {
+        return currentTick;
     }
 
     public static void executePendingTasks()
     {
-        int tasksThisTick = 0;
-        while( tasksThisTick < MAX_TASKS_PER_TICK )
+        // Move onto the next tick and cool down the global executor. We're allowed to execute if we have _any_ time
+        // allocated for this tick. This means we'll stick much closer to doing MAX_TICK_TIME work every tick.
+        //
+        // Of course, we'll go over the MAX_TICK_TIME most of the time, but eventually that overrun will accumulate
+        // and we'll skip a whole tick - bringing the average back down again.
+        currentTick++;
+        budget += Math.min( budget + ComputerCraft.maxMainGlobalTime, ComputerCraft.maxMainGlobalTime );
+        canExecute = budget > 0;
+
+        // Cool down any warm computers.
+        cooling.removeIf( MainThreadExecutor::tickCooling );
+
+        if( !canExecute ) return;
+
+        // Run until we meet the deadline.
+        long start = System.nanoTime();
+        long deadline = start + budget;
+        while( true )
         {
-            ITask task = null;
-            synchronized( m_outstandingTasks )
+            MainThreadExecutor executor;
+            synchronized( executors )
             {
-                task = m_outstandingTasks.poll();
+                executor = executors.pollFirst();
             }
-            if( task != null )
-            {
-                long start = System.nanoTime();
-                task.execute();
+            if( executor == null ) break;
 
-                long stop = System.nanoTime();
-                Computer computer = task.getOwner();
-                if( computer != null ) Tracking.addServerTiming( computer, stop - start );
+            long taskStart = System.nanoTime();
+            executor.execute();
 
-                ++tasksThisTick;
-            }
-            else
+            long taskStop = System.nanoTime();
+            synchronized( executors )
             {
-                break;
+                if( executor.afterExecute( taskStop - taskStart ) ) executors.add( executor );
+
+                // Compute the new minimum time (including the next task on the queue too). Note that this may also include
+                // time spent in external tasks.
+                long newMinimum = executor.virtualTime;
+                if( !executors.isEmpty() )
+                {
+                    MainThreadExecutor next = executors.first();
+                    if( next.virtualTime < newMinimum ) newMinimum = next.virtualTime;
+                }
+                minimumTime = Math.max( minimumTime, newMinimum );
             }
+
+            if( taskStop >= deadline ) break;
+        }
+
+        consumeTime( System.nanoTime() - start );
+    }
+
+    public static void reset()
+    {
+        currentTick = 0;
+        budget = 0;
+        canExecute = true;
+        minimumTime = 0;
+        lastTaskId.set( 0 );
+        cooling.clear();
+        synchronized( executors )
+        {
+            executors.clear();
         }
     }
 }

src/main/java/dan200/computercraft/core/computer/MainThreadExecutor.java

@@ -0,0 +1,250 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2019. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+
+package dan200.computercraft.core.computer;
+
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
+import dan200.computercraft.core.tracking.Tracking;
+import dan200.computercraft.shared.turtle.core.TurtleBrain;
+import net.minecraft.tileentity.TileEntity;
+
+import javax.annotation.Nonnull;
+import java.util.ArrayDeque;
+import java.util.Queue;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Keeps track of tasks that a {@link Computer} should run on the main thread and how long that has been spent executing
+ * them.
+ *
+ * This provides rate-limiting mechanism for tasks enqueued with {@link Computer#queueMainThread(Runnable)}, but also
+ * those run elsewhere (such as during the turtle's tick - see {@link TurtleBrain#update()}). In order to handle this,
+ * the executor goes through three stages:
+ *
+ * When {@link State#COOL}, the computer is allocated {@link ComputerCraft#maxMainComputerTime}ns to execute any work
+ * this tick. At the beginning of the tick, we execute as many {@link MainThread} tasks as possible, until our timeframe
+ * or the global time frame has expired.
+ *
+ * Then, when other objects (such as {@link TileEntity}) are ticked, we update how much time we've used using
+ * {@link IWorkMonitor#trackWork(long, TimeUnit)}.
+ *
+ * Now, if anywhere during this period, we use more than our allocated time slice, the executor is marked as
+ * {@link State#HOT}. This means it will no longer be able to execute {@link MainThread} tasks (though will still
+ * execute tile entity tasks, in order to prevent the main thread from exhausting work every tick).
+ *
+ * At the beginning of the next tick, we increment the budget e by {@link ComputerCraft#maxMainComputerTime} and any
+ * {@link State#HOT} executors are marked as {@link State#COOLING}. They will remain cooling until their budget is
+ * fully replenished (is equal to {@link ComputerCraft#maxMainComputerTime}). Note, this is different to
+ * {@link MainThread}, which allows running when it has any budget left. When cooling, <em>no</em> tasks are executed -
+ * be they on the tile entity or main thread.
+ *
+ * This mechanism means that, on average, computers will use at most {@link ComputerCraft#maxMainComputerTime}ns per
+ * second, but one task source will not prevent others from executing.
+ *
+ * @see MainThread
+ * @see IWorkMonitor
+ * @see Computer#getMainThreadMonitor()
+ * @see Computer#queueMainThread(Runnable)
+ */
+final class MainThreadExecutor implements IWorkMonitor
+{
+    /**
+     * The maximum number of {@link MainThread} tasks allowed on the queue.
+     */
+    private static final int MAX_TASKS = 5000;
+
+    private final Computer computer;
+
+    /**
+     * A lock used for any changes to {@link #tasks}, or {@link #onQueue}. This will be
+     * used on the main thread, so locks should be kept as brief as possible.
+     */
+    private final Object queueLock = new Object();
+
+    /**
+     * The queue of tasks which should be executed.
+     *
+     * @see #queueLock
+     */
+    private final Queue<Runnable> tasks = new ArrayDeque<>( 4 );
+
+    /**
+     * Determines if this executor is currently present on the queue.
+     *
+     * This should be true iff {@link #tasks} is non-empty.
+     *
+     * @see #queueLock
+     * @see #enqueue(Runnable)
+     * @see #afterExecute(long)
+     */
+    volatile boolean onQueue;
+
+    /**
+     * The remaining budgeted time for this tick. This may be negative, in the case that we've gone over budget.
+     *
+     * @see #tickCooling()
+     * @see #consumeTime(long)
+     */
+    private long budget = 0;
+
+    /**
+     * The last tick that {@link #budget} was updated.
+     *
+     * @see #tickCooling()
+     * @see #consumeTime(long)
+     */
+    private int currentTick = -1;
+
+    /**
+     * The current state of this executor.
+     *
+     * @see #canWork()
+     */
+    private State state = State.COOL;
+
+    private long pendingTime;
+
+    long virtualTime;
+
+    MainThreadExecutor( Computer computer )
+    {
+        this.computer = computer;
+    }
+
+    /**
+     * Push a task onto this executor's queue, pushing it onto the {@link MainThread} if needed.
+     *
+     * @param runnable The task to run on the main thread.
+     * @return Whether this task was enqueued (namely, was there space).
+     */
+    boolean enqueue( Runnable runnable )
+    {
+        synchronized( queueLock )
+        {
+            if( tasks.size() >= MAX_TASKS || !tasks.offer( runnable ) ) return false;
+            if( !onQueue && state == State.COOL ) MainThread.queue( this, true );
+            return true;
+        }
+    }
+
+    void execute()
+    {
+        if( state != State.COOL ) return;
+
+        Runnable task;
+        synchronized( queueLock )
+        {
+            task = tasks.poll();
+        }
+
+        if( task != null ) task.run();
+    }
+
+    /**
+     * Update the time taken to run an {@link #enqueue(Runnable)} task.
+     *
+     * @param time The time some task took to run.
+     * @return Whether this should be added back to the queue.
+     */
+    boolean afterExecute( long time )
+    {
+        consumeTime( time );
+
+        synchronized( queueLock )
+        {
+            virtualTime += time;
+            updateTime();
+            if( state != State.COOL || tasks.isEmpty() ) return onQueue = false;
+            return true;
+        }
+    }
+
+    /**
+     * Whether we should execute "external" tasks (ones not part of {@link #tasks}).
+     *
+     * @return Whether we can execute external tasks.
+     */
+    @Override
+    public boolean canWork()
+    {
+        return state != State.COOLING && MainThread.canExecute();
+    }
+
+    @Override
+    public boolean shouldWork()
+    {
+        return state == State.COOL && MainThread.canExecute();
+    }
+
+    @Override
+    public void trackWork( long time, @Nonnull TimeUnit unit )
+    {
+        long nanoTime = unit.toNanos( time );
+        synchronized( queueLock )
+        {
+            pendingTime += nanoTime;
+        }
+
+        consumeTime( nanoTime );
+        MainThread.consumeTime( nanoTime );
+    }
+
+    private void consumeTime( long time )
+    {
+        Tracking.addServerTiming( computer, time );
+
+        // Reset the budget if moving onto a new tick. We know this is safe, as this will only have happened if
+        // #tickCooling() isn't called, and so we didn't overrun the previous tick.
+        if( currentTick != MainThread.currentTick() )
+        {
+            currentTick = MainThread.currentTick();
+            budget = ComputerCraft.maxMainComputerTime;
+        }
+
+        budget -= time;
+
+        // If we've gone over our limit, mark us as having to cool down.
+        if( budget < 0 && state == State.COOL )
+        {
+            state = State.HOT;
+            MainThread.cooling( this );
+        }
+    }
+
+    /**
+     * Move this executor forward one tick, replenishing the budget by {@link ComputerCraft#maxMainComputerTime}.
+     *
+     * @return Whether this executor has cooled down, and so is safe to run again.
+     */
+    boolean tickCooling()
+    {
+        state = State.COOLING;
+        currentTick = MainThread.currentTick();
+        budget += Math.min( budget + ComputerCraft.maxMainComputerTime, ComputerCraft.maxMainComputerTime );
+        if( budget < ComputerCraft.maxMainComputerTime ) return false;
+
+        state = State.COOL;
+        synchronized( queueLock )
+        {
+            if( !tasks.isEmpty() && !onQueue ) MainThread.queue( this, false );
+        }
+        return true;
+    }
+
+    void updateTime()
+    {
+        virtualTime += pendingTime;
+        pendingTime = 0;
+    }
+
+    private enum State
+    {
+        COOL,
+        HOT,
+        COOLING,
+    }
+}

src/main/java/dan200/computercraft/core/lua/CobaltLuaMachine.java

@@ -9,7 +9,6 @@
 import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.lua.*;
 import dan200.computercraft.core.computer.Computer;
-import dan200.computercraft.core.computer.ITask;
 import dan200.computercraft.core.computer.MainThread;
 import dan200.computercraft.core.computer.TimeoutState;
 import dan200.computercraft.core.tracking.Tracking;
@@ -536,53 +535,36 @@ public long issueMainThreadTask( @Nonnull final ILuaTask task ) throws LuaExcept
         {
             // Issue command
             final long taskID = MainThread.getUniqueTaskID();
-            final ITask iTask = new ITask()
-            {
-                @Nonnull
-                @Override
-                public Computer getOwner()
+            final Runnable iTask = () -> {
+                try
                 {
-                    return m_computer;
+                    Object[] results = task.execute();
+                    if( results != null )
+                    {
+                        Object[] eventArguments = new Object[results.length + 2];
+                        eventArguments[0] = taskID;
+                        eventArguments[1] = true;
+                        System.arraycopy( results, 0, eventArguments, 2, results.length );
+                        m_computer.queueEvent( "task_complete", eventArguments );
+                    }
+                    else
+                    {
+                        m_computer.queueEvent( "task_complete", new Object[] { taskID, true } );
+                    }
                 }
-
-                @Override
-                public void execute()
+                catch( LuaException e )
                 {
-                    try
-                    {
-                        Object[] results = task.execute();
-                        if( results != null )
-                        {
-                            Object[] eventArguments = new Object[results.length + 2];
-                            eventArguments[0] = taskID;
-                            eventArguments[1] = true;
-                            System.arraycopy( results, 0, eventArguments, 2, results.length );
-                            m_computer.queueEvent( "task_complete", eventArguments );
-                        }
-                        else
-                        {
-                            m_computer.queueEvent( "task_complete", new Object[] { taskID, true } );
-                        }
-                    }
-                    catch( LuaException e )
-                    {
-                        m_computer.queueEvent( "task_complete", new Object[] {
-                            taskID, false, e.getMessage()
-                        } );
-                    }
-                    catch( Throwable t )
-                    {
-                        if( ComputerCraft.logPeripheralErrors )
-                        {
-                            ComputerCraft.log.error( "Error running task", t );
-                        }
-                        m_computer.queueEvent( "task_complete", new Object[] {
-                            taskID, false, "Java Exception Thrown: " + t.toString()
-                        } );
-                    }
+                    m_computer.queueEvent( "task_complete", new Object[] { taskID, false, e.getMessage() } );
+                }
+                catch( Throwable t )
+                {
+                    if( ComputerCraft.logPeripheralErrors ) ComputerCraft.log.error( "Error running task", t );
+                    m_computer.queueEvent( "task_complete", new Object[] {
+                        taskID, false, "Java Exception Thrown: " + t.toString()
+                    } );
                 }
             };
-            if( MainThread.queueTask( iTask ) )
+            if( m_computer.queueMainThread( iTask ) )
             {
                 return taskID;
             }

src/main/java/dan200/computercraft/shared/Config.java

@@ -23,6 +23,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.TimeUnit;
 
 import static dan200.computercraft.ComputerCraft.DEFAULT_HTTP_BLACKLIST;
 import static dan200.computercraft.ComputerCraft.DEFAULT_HTTP_WHITELIST;
@@ -32,6 +33,7 @@ public class Config
     private static final int MODEM_MAX_RANGE = 100000;
 
     private static final String CATEGORY_GENERAL = "general";
+    private static final String CATEGORY_EXECUTION = "execution";
     private static final String CATEGORY_HTTP = "http";
     private static final String CATEGORY_PERIPHERAL = "peripheral";
     private static final String CATEGORY_TURTLE = "turtle";
@@ -44,9 +46,12 @@ public class Config
     private static Property disableLua51Features;
     private static Property defaultComputerSettings;
     private static Property debugEnabled;
-    private static Property computerThreads;
     private static Property logComputerErrors;
 
+    private static Property computerThreads;
+    private static Property maxMainGlobalTime;
+    private static Property maxMainComputerTime;
+
     private static Property httpEnable;
     private static Property httpWebsocketEnable;
     private static Property httpWhitelist;
@@ -97,21 +102,16 @@ public static void load( File configFile )
             maximumFilesOpen.setMinValue( 0 );
 
             disableLua51Features = config.get( CATEGORY_GENERAL, "disable_lua51_features", ComputerCraft.disable_lua51_features );
-            disableLua51Features.setComment( "Set this to true to disable Lua 5.1 functions that will be removed in a future update. Useful for ensuring forward compatibility of your programs now." );
+            disableLua51Features.setComment( "Set this to true to disable Lua 5.1 functions that will be removed in a future " +
+                "update. Useful for ensuring forward compatibility of your programs now." );
 
             defaultComputerSettings = config.get( CATEGORY_GENERAL, "default_computer_settings", ComputerCraft.default_computer_settings );
-            defaultComputerSettings.setComment( "A comma seperated list of default system settings to set on new computers. Example: \"shell.autocomplete=false,lua.autocomplete=false,edit.autocomplete=false\" will disable all autocompletion" );
+            defaultComputerSettings.setComment( "A comma seperated list of default system settings to set on new computers. Example: " +
+                "\"shell.autocomplete=false,lua.autocomplete=false,edit.autocomplete=false\" will disable all autocompletion" );
 
             debugEnabled = config.get( CATEGORY_GENERAL, "debug_enabled", ComputerCraft.debug_enable );
             debugEnabled.setComment( "Enable Lua's debug library. This is sandboxed to each computer, so is generally safe to be used by players." );
 
-            computerThreads = config.get( CATEGORY_GENERAL, "computer_threads", ComputerCraft.computer_threads );
-            computerThreads
-                .setMinValue( 1 )
-                .setRequiresMcRestart( true )
-                .setComment( "Set the number of threads computers can run on. A higher number means more computers can run at once, but may induce lag.\n" +
-                    "Please note that some mods may not work with a thread count higher than 1. Use with caution." );
-
             logComputerErrors = config.get( CATEGORY_GENERAL, "log_computer_errors", ComputerCraft.logPeripheralErrors );
             logComputerErrors.setComment( "Log exceptions thrown by peripherals and other Lua objects.\n" +
                 "This makes it easier for mod authors to debug problems, but may result in log spam should people use buggy methods." );
@@ -119,7 +119,42 @@ public static void load( File configFile )
             setOrder(
                 CATEGORY_GENERAL,
                 computerSpaceLimit, floppySpaceLimit, maximumFilesOpen,
-                disableLua51Features, defaultComputerSettings, debugEnabled, computerThreads, logComputerErrors
+                disableLua51Features, defaultComputerSettings, debugEnabled, logComputerErrors
+            );
+        }
+
+        { // Execution
+            renameProperty( CATEGORY_GENERAL, "computer_threads", CATEGORY_EXECUTION, "computer_threads" );
+
+            config.getCategory( CATEGORY_EXECUTION )
+                .setComment( "Controls execution behaviour of computers. This is largely intended for fine-tuning " +
+                    "servers, and generally shouldn't need to be touched" );
+
+            computerThreads = config.get( CATEGORY_EXECUTION, "computer_threads", ComputerCraft.computer_threads );
+            computerThreads
+                .setMinValue( 1 )
+                .setRequiresMcRestart( true )
+                .setComment( "Set the number of threads computers can run on. A higher number means more computers can " +
+                    "run at once, but may induce lag.\n" +
+                    "Please note that some mods may not work with a thread count higher than 1. Use with caution." );
+
+            maxMainGlobalTime = config.get( CATEGORY_EXECUTION, "max_main_global_time", (int) TimeUnit.NANOSECONDS.toMillis( ComputerCraft.maxMainGlobalTime ) );
+            maxMainGlobalTime
+                .setMinValue( 1 )
+                .setComment( "The maximum time that can be spent executing tasks in a single tick, in milliseconds.\n" +
+                    "Note, we will quite possibly go over this limit, as there's no way to tell how long a will take - this aims " +
+                    "to be the upper bound of the average time." );
+
+            maxMainComputerTime = config.get( CATEGORY_EXECUTION, "max_main_computer_time", (int) TimeUnit.NANOSECONDS.toMillis( ComputerCraft.maxMainComputerTime ) );
+            maxMainComputerTime
+                .setMinValue( 1 )
+                .setComment( "The ideal maximum time a computer can execute for in a tick, in milliseconds.\n" +
+                    "Note, we will quite possibly go over this limit, as there's no way to tell how long a will take - this aims " +
+                    "to be the upper bound of the average time." );
+
+            setOrder(
+                CATEGORY_EXECUTION,
+                computerThreads, maxMainGlobalTime, maxMainComputerTime
             );
         }
 
@@ -129,20 +164,28 @@ public static void load( File configFile )
             renameProperty( CATEGORY_GENERAL, "http_whitelist", CATEGORY_HTTP, "whitelist" );
             renameProperty( CATEGORY_GENERAL, "http_blacklist", CATEGORY_HTTP, "blacklist" );
 
+            config.getCategory( CATEGORY_HTTP )
+                .setComment( "Controls the HTTP API" );
+
             httpEnable = config.get( CATEGORY_HTTP, "enabled", ComputerCraft.http_enable );
-            httpEnable.setComment( "Enable the \"http\" API on Computers (see \"http_whitelist\" and \"http_blacklist\" for more fine grained control than this)" );
+            httpEnable.setComment( "Enable the \"http\" API on Computers (see \"http_whitelist\" and \"http_blacklist\" for " +
+                "more fine grained control than this)" );
 
             httpWebsocketEnable = config.get( CATEGORY_HTTP, "websocket_enabled", ComputerCraft.http_websocket_enable );
             httpWebsocketEnable.setComment( "Enable use of http websockets. This requires the \"http_enable\" option to also be true." );
 
             httpWhitelist = config.get( CATEGORY_HTTP, "whitelist", DEFAULT_HTTP_WHITELIST );
-            httpWhitelist.setComment( "A list of wildcards for domains or IP ranges that can be accessed through the \"http\" API on Computers.\n" +
-                "Set this to \"*\" to access to the entire internet. Example: \"*.pastebin.com\" will restrict access to just subdomains of pastebin.com.\n" +
+            httpWhitelist.setComment( "A list of wildcards for domains or IP ranges that can be accessed through the " +
+                "\"http\" API on Computers.\n" +
+                "Set this to \"*\" to access to the entire internet. Example: \"*.pastebin.com\" will restrict access to " +
+                "just subdomains of pastebin.com.\n" +
                 "You can use domain names (\"pastebin.com\"), wilcards (\"*.pastebin.com\") or CIDR notation (\"127.0.0.0/8\")." );
 
             httpBlacklist = config.get( CATEGORY_HTTP, "blacklist", DEFAULT_HTTP_BLACKLIST );
-            httpBlacklist.setComment( "A list of wildcards for domains or IP ranges that cannot be accessed through the \"http\" API on Computers.\n" +
-                "If this is empty then all whitelisted domains will be accessible. Example: \"*.github.com\" will block access to all subdomains of github.com.\n" +
+            httpBlacklist.setComment( "A list of wildcards for domains or IP ranges that cannot be accessed through the " +
+                "\"http\" API on Computers.\n" +
+                "If this is empty then all whitelisted domains will be accessible. Example: \"*.github.com\" will block " +
+                "access to all subdomains of github.com.\n" +
                 "You can use domain names (\"pastebin.com\"), wilcards (\"*.pastebin.com\") or CIDR notation (\"127.0.0.0/8\")." );
 
             httpTimeout = config.get( CATEGORY_HTTP, "timeout", ComputerCraft.httpTimeout );
@@ -150,15 +193,18 @@ public static void load( File configFile )
             httpTimeout.setMinValue( 0 );
 
             httpMaxRequests = config.get( CATEGORY_HTTP, "max_requests", ComputerCraft.httpMaxRequests );
-            httpMaxRequests.setComment( "The number of http requests a computer can make at one time. Additional requests will be queued, and sent when the running requests have finished. Set to 0 for unlimited." );
+            httpMaxRequests.setComment( "The number of http requests a computer can make at one time. Additional requests " +
+                "will be queued, and sent when the running requests have finished. Set to 0 for unlimited." );
             httpMaxRequests.setMinValue( 0 );
 
             httpMaxDownload = config.get( CATEGORY_HTTP, "max_download", (int) ComputerCraft.httpMaxDownload );
-            httpMaxDownload.setComment( "The maximum size (in bytes) that a computer can download in a single request. Note that responses may receive more data than allowed, but this data will not be returned to the client." );
+            httpMaxDownload.setComment( "The maximum size (in bytes) that a computer can download in a single request. " +
+                "Note that responses may receive more data than allowed, but this data will not be returned to the client." );
             httpMaxDownload.setMinValue( 0 );
 
             httpMaxUpload = config.get( CATEGORY_HTTP, "max_upload", (int) ComputerCraft.httpMaxUpload );
-            httpMaxUpload.setComment( "The maximum size (in bytes) that a computer can upload in a single request. This includes headers and POST text." );
+            httpMaxUpload.setComment( "The maximum size (in bytes) that a computer can upload in a single request. This " +
+                "includes headers and POST text." );
             httpMaxUpload.setMinValue( 0 );
 
             httpMaxWebsockets = config.get( CATEGORY_HTTP, "max_websockets", ComputerCraft.httpMaxWebsockets );
@@ -185,6 +231,9 @@ public static void load( File configFile )
             renameProperty( CATEGORY_GENERAL, "modem_highAltitudeRangeDuringStorm", CATEGORY_PERIPHERAL, "modem_high_altitude_range_during_storm" );
             renameProperty( CATEGORY_GENERAL, "maxNotesPerTick", CATEGORY_PERIPHERAL, "max_notes_per_tick" );
 
+            config.getCategory( CATEGORY_PERIPHERAL )
+                .setComment( "Various options relating to peripherals." );
+
             commandBlockEnabled = config.get( CATEGORY_PERIPHERAL, "command_block_enabled", ComputerCraft.enableCommandBlock );
             commandBlockEnabled.setComment( "Enable Command Block peripheral support" );
 
@@ -226,6 +275,9 @@ public static void load( File configFile )
             renameProperty( CATEGORY_GENERAL, "turtlesCanPush", CATEGORY_TURTLE, "can_push" );
             renameProperty( CATEGORY_GENERAL, "turtle_disabled_actions", CATEGORY_TURTLE, "disabled_actions" );
 
+            config.getCategory( CATEGORY_HTTP )
+                .setComment( "Various options relating to turtles." );
+
             turtlesNeedFuel = config.get( CATEGORY_TURTLE, "need_fuel", ComputerCraft.turtlesNeedFuel );
             turtlesNeedFuel.setComment( "Set whether Turtles require fuel to move" );
 
@@ -238,10 +290,12 @@ public static void load( File configFile )
             advancedTurtleFuelLimit.setMinValue( 0 );
 
             turtlesObeyBlockProtection = config.get( CATEGORY_TURTLE, "obey_block_protection", ComputerCraft.turtlesObeyBlockProtection );
-            turtlesObeyBlockProtection.setComment( "If set to true, Turtles will be unable to build, dig, or enter protected areas (such as near the server spawn point)" );
+            turtlesObeyBlockProtection.setComment( "If set to true, Turtles will be unable to build, dig, or enter protected " +
+                "areas (such as near the server spawn point)" );
 
             turtlesCanPush = config.get( CATEGORY_TURTLE, "can_push", ComputerCraft.turtlesCanPush );
-            turtlesCanPush.setComment( "If set to true, Turtles will push entities out of the way instead of stopping if there is space to do so" );
+            turtlesCanPush.setComment( "If set to true, Turtles will push entities out of the way instead of stopping if " +
+                "there is space to do so" );
 
             turtleDisabledActions = config.get( CATEGORY_TURTLE, "disabled_actions", new String[0] );
             turtleDisabledActions.setComment( "A list of turtle actions which are disabled." );
@@ -252,11 +306,12 @@ public static void load( File configFile )
             );
         }
 
-        setupLanguage( config.getCategory( CATEGORY_GENERAL ), "gui.computercraft:config" );
         for( String child : config.getCategoryNames() )
         {
-            if( child.equals( CATEGORY_GENERAL ) ) continue;
-            setupLanguage( config.getCategory( child ), "gui.computercraft:config." + child );
+            setupLanguage(
+                config.getCategory( child ),
+                child.equals( CATEGORY_GENERAL ) ? "gui.computercraft:config" : "gui.computercraft:config." + child
+            );
         }
 
         sync();
@@ -374,9 +429,13 @@ public static void sync()
         ComputerCraft.disable_lua51_features = disableLua51Features.getBoolean();
         ComputerCraft.default_computer_settings = defaultComputerSettings.getString();
         ComputerCraft.debug_enable = debugEnabled.getBoolean();
-        ComputerCraft.computer_threads = computerThreads.getInt();
         ComputerCraft.logPeripheralErrors = logComputerErrors.getBoolean();
 
+        // Execution
+        ComputerCraft.computer_threads = computerThreads.getInt();
+        ComputerCraft.maxMainGlobalTime = TimeUnit.MILLISECONDS.toNanos( Math.max( 1, maxMainGlobalTime.getLong() ) );
+        ComputerCraft.maxMainComputerTime = TimeUnit.MILLISECONDS.toNanos( Math.max( 1, maxMainComputerTime.getLong() ) );
+
         // HTTP
         ComputerCraft.http_enable = httpEnable.getBoolean();
         ComputerCraft.http_websocket_enable = httpWebsocketEnable.getBoolean();

src/main/java/dan200/computercraft/shared/peripheral/modem/wired/WiredModemPeripheral.java

@@ -16,8 +16,7 @@
 import dan200.computercraft.api.network.wired.IWiredSender;
 import dan200.computercraft.api.peripheral.IComputerAccess;
 import dan200.computercraft.api.peripheral.IPeripheral;
-import dan200.computercraft.core.computer.Computer;
-import dan200.computercraft.core.computer.IComputerOwned;
+import dan200.computercraft.api.peripheral.IWorkMonitor;
 import dan200.computercraft.shared.peripheral.modem.ModemPeripheral;
 import dan200.computercraft.shared.peripheral.modem.ModemState;
 import net.minecraft.world.World;
@@ -267,7 +266,7 @@ private RemotePeripheralWrapper getWrapper( IComputerAccess computer, String rem
         return wrappers == null ? null : wrappers.get( remoteName );
     }
 
-    private static class RemotePeripheralWrapper implements IComputerAccess, IComputerOwned
+    private static class RemotePeripheralWrapper implements IComputerAccess
     {
         private final WiredModemElement m_element;
         private final IPeripheral m_peripheral;
@@ -376,6 +375,13 @@ public void queueEvent( @Nonnull String event, Object[] arguments )
             m_computer.queueEvent( event, arguments );
         }
 
+        @Nullable
+        @Override
+        public IWorkMonitor getMainThreadMonitor()
+        {
+            return m_computer.getMainThreadMonitor();
+        }
+
         @Nonnull
         @Override
         public String getAttachmentName()
@@ -402,12 +408,5 @@ public IPeripheral getAvailablePeripheral( @Nonnull String name )
                 return m_element.getRemotePeripherals().get( name );
             }
         }
-
-        @Nullable
-        @Override
-        public Computer getComputer()
-        {
-            return m_computer instanceof IComputerOwned ? ((IComputerOwned) m_computer).getComputer() : null;
-        }
     }
 }

src/main/java/dan200/computercraft/shared/turtle/core/TurtleBrain.java

@@ -13,7 +13,6 @@
 import dan200.computercraft.api.lua.LuaException;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.api.turtle.*;
-import dan200.computercraft.core.tracking.Tracking;
 import dan200.computercraft.shared.computer.blocks.ComputerProxy;
 import dan200.computercraft.shared.computer.blocks.TileComputerBase;
 import dan200.computercraft.shared.computer.core.ComputerFamily;
@@ -41,6 +40,7 @@
 
 import javax.annotation.Nonnull;
 import java.util.*;
+import java.util.concurrent.TimeUnit;
 
 public class TurtleBrain implements ITurtleAccess
 {
@@ -957,53 +957,50 @@ private void updatePeripherals( ServerComputer serverComputer )
 
     private void updateCommands()
     {
-        if( m_animation == TurtleAnimation.None )
+        if( m_animation != TurtleAnimation.None || m_commandQueue.isEmpty() ) return;
+
+        // If we've got a computer, ensure that we're allowed to perform work.
+        ServerComputer computer = m_owner.getServerComputer();
+        if( computer != null && !computer.getComputer().getMainThreadMonitor().canWork() ) return;
+
+        // Pull a new command
+        TurtleCommandQueueEntry nextCommand = m_commandQueue.poll();
+        if( nextCommand == null ) return;
+
+        // Execute the command
+        long start = System.nanoTime();
+        TurtleCommandResult result = nextCommand.command.execute( this );
+        long end = System.nanoTime();
+
+        // Dispatch the callback
+        if( computer == null ) return;
+        computer.getComputer().getMainThreadMonitor().trackWork( end - start, TimeUnit.NANOSECONDS );
+        int callbackID = nextCommand.callbackID;
+        if( callbackID < 0 ) return;
+
+        if( result != null && result.isSuccess() )
         {
-            // Pull a new command
-            TurtleCommandQueueEntry nextCommand = m_commandQueue.poll();
-            if( nextCommand != null )
+            Object[] results = result.getResults();
+            if( results != null )
             {
-                ServerComputer computer = m_owner.getServerComputer();
-
-                // Execute the command
-                long start = System.nanoTime();
-                TurtleCommandResult result = nextCommand.command.execute( this );
-                long end = System.nanoTime();
-
-                // Dispatch the callback
-                if( computer != null )
-                {
-                    Tracking.addServerTiming( computer.getComputer(), end - start );
-                    int callbackID = nextCommand.callbackID;
-                    if( callbackID >= 0 )
-                    {
-                        if( result != null && result.isSuccess() )
-                        {
-                            Object[] results = result.getResults();
-                            if( results != null )
-                            {
-                                Object[] arguments = new Object[results.length + 2];
-                                arguments[0] = callbackID;
-                                arguments[1] = true;
-                                System.arraycopy( results, 0, arguments, 2, results.length );
-                                computer.queueEvent( "turtle_response", arguments );
-                            }
-                            else
-                            {
-                                computer.queueEvent( "turtle_response", new Object[] {
-                                    callbackID, true
-                                } );
-                            }
-                        }
-                        else
-                        {
-                            computer.queueEvent( "turtle_response", new Object[] {
-                                callbackID, false, result != null ? result.getErrorMessage() : null
-                            } );
-                        }
-                    }
-                }
+                Object[] arguments = new Object[results.length + 2];
+                arguments[0] = callbackID;
+                arguments[1] = true;
+                System.arraycopy( results, 0, arguments, 2, results.length );
+                computer.queueEvent( "turtle_response", arguments );
             }
+            else
+            {
+                computer.queueEvent( "turtle_response", new Object[] {
+                    callbackID, true
+                } );
+            }
+        }
+        else
+        {
+            computer.queueEvent( "turtle_response", new Object[] {
+                callbackID, false, result != null ? result.getErrorMessage() : null
+            } );
         }
     }
 

src/main/resources/assets/computercraft/lang/de_de.lang

@@ -58,7 +58,7 @@ commands.computercraft.dump.usage=[ID]
 commands.computercraft.dump.action=Zeigt mehr Informationen über einen Computer
 
 commands.computercraft.shutdown.synopsis=Fährt den Computer aus der Ferne herunter.
-commands.computercraft.shutdown.desc=Fährt die angegebenen Computer herunter. Falls keine Computer angegeben sind, werden alle heruntergefahren. Der Computer kann entweder über seine Instanz ID (z.B. 123), seine Computer ID (z.B. #123) oder seinen Namen (z.B. "@Mein Computer") angegeben werden. 
+commands.computercraft.shutdown.desc=Fährt die angegebenen Computer herunter. Falls keine Computer angegeben sind, werden alle heruntergefahren. Der Computer kann entweder über seine Instanz ID (z.B. 123), seine Computer ID (z.B. #123) oder seinen Namen (z.B. "@Mein Computer") angegeben werden.
 commands.computercraft.shutdown.usage=[IDs...]
 commands.computercraft.shutdown.done=Fährt die Computer %s/%s herunter
 
@@ -156,9 +156,10 @@ gui.computercraft:config.maximum_open_files=Maximalanzahl an gleichzeitig offene
 gui.computercraft:config.disable_lua51_features=Lua 5.1-Funktionen deaktivieren
 gui.computercraft:config.default_computer_settings=Computer-Standardeinstellungen
 gui.computercraft:config.debug_enabled=Debug-Library aktivieren
-gui.computercraft:config.computer_threads=Computer Threads
 gui.computercraft:config.log_computer_errors=Computerfehler loggen
 
+gui.computercraft:config.execution.computer_threads=Computer Threads
+
 gui.computercraft:config.http=HTTP
 gui.computercraft:config.http.enabled=HTTP-API aktivieren
 gui.computercraft:config.http.websocket_enabled=Websockets aktivieren

src/main/resources/assets/computercraft/lang/en_us.lang

@@ -156,9 +156,13 @@ gui.computercraft:config.maximum_open_files=Maximum files open per computer
 gui.computercraft:config.disable_lua51_features=Disable Lua 5.1 features
 gui.computercraft:config.default_computer_settings=Default Computer settings
 gui.computercraft:config.debug_enabled=Enable debug library
-gui.computercraft:config.computer_threads=Computer threads
 gui.computercraft:config.log_computer_errors=Log computer errors
 
+gui.computercraft:config.execution=Execution
+gui.computercraft:config.execution.computer_threads=Computer threads
+gui.computercraft:config.execution.max_main_global_time=Server tick global time limit
+gui.computercraft:config.execution.max_main_computer_time=Server tick computer time limit
+
 gui.computercraft:config.http=HTTP
 gui.computercraft:config.http.enabled=Enable the HTTP API
 gui.computercraft:config.http.websocket_enabled=Enable websockets

src/main/resources/assets/computercraft/lang/it_it.lang

@@ -56,9 +56,10 @@ gui.computercraft:config.maximum_open_files=Massimo file aperti per computer
 gui.computercraft:config.disable_lua51_features=Disattiva features Lua 5.1
 gui.computercraft:config.default_computer_settings=Impostazioni Computer predefinite
 gui.computercraft:config.debug_enabled=Attiva libreria di debug
-gui.computercraft:config.computer_threads=Threads computer
 gui.computercraft:config.log_computer_errors=Salva errori computer
 
+gui.computercraft:config.execution.computer_threads=Threads computer
+
 gui.computercraft:config.http=HTTP
 gui.computercraft:config.http.enabled=Attiva l'API HTTP
 gui.computercraft:config.http.websocket_enabled=Attiva websocket

src/main/resources/assets/computercraft/lang/pt_br.lang

@@ -56,9 +56,10 @@ gui.computercraft:config.maximum_open_files=Número máximo de arquivos em um co
 gui.computercraft:config.disable_lua51_features=Desabilitar funcionalidade da Lua 5.1
 gui.computercraft:config.default_computer_settings=Configurações padrão para Computadores
 gui.computercraft:config.debug_enabled=Habilitar biblioteca de debug
-gui.computercraft:config.computer_threads=Threads por computador
 gui.computercraft:config.log_computer_errors=Registrar erros de computadores
 
+gui.computercraft:config.execution.computer_threads=Threads por computador
+
 gui.computercraft:config.http=HTTP
 gui.computercraft:config.http.enabled=Habilitar a biblioteca de HTTP
 gui.computercraft:config.http.websocket_enabled=Habilitar websockets

src/main/resources/assets/computercraft/lang/sv_se.lang

@@ -56,9 +56,10 @@ gui.computercraft:config.maximum_open_files=Max antal filer öppna per dator
 gui.computercraft:config.disable_lua51_features=Avaktivera Lua 5.1 funktioner
 gui.computercraft:config.default_computer_settings=Standard Datorinställningar
 gui.computercraft:config.debug_enabled=Aktivera debug bibliotek
-gui.computercraft:config.computer_threads=Dator trådar
 gui.computercraft:config.log_computer_errors=Logga datorfel
 
+gui.computercraft:config.execution.computer_threads=Dator trådar
+
 gui.computercraft:config.http=HTTP
 gui.computercraft:config.http.enabled=Aktivera HTTP API
 gui.computercraft:config.http.websocket_enabled=Aktivera websockets