Add basic JMX monitoring on dedicated servers

Closes #482

src/main/java/dan200/computercraft/core/tracking/ComputerMBean.java

@@ -0,0 +1,155 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2021. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.core.tracking;
+
+import com.google.common.base.CaseFormat;
+import dan200.computercraft.ComputerCraft;
+import dan200.computercraft.core.computer.Computer;
+import net.minecraft.util.text.LanguageMap;
+
+import javax.annotation.Nonnull;
+import javax.management.*;
+import java.lang.management.ManagementFactory;
+import java.util.*;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.LongSupplier;
+
+public final class ComputerMBean implements DynamicMBean, Tracker
+{
+    private static final Set<TrackingField> SKIP = new HashSet<>( Arrays.asList(
+        TrackingField.TASKS, TrackingField.TOTAL_TIME, TrackingField.AVERAGE_TIME, TrackingField.MAX_TIME,
+        TrackingField.SERVER_COUNT, TrackingField.SERVER_TIME
+    ) );
+
+    private static ComputerMBean instance;
+
+    private final Map<String, LongSupplier> attributes = new HashMap<>();
+    private final Map<TrackingField, Counter> values = new HashMap<>();
+    private final MBeanInfo info;
+
+    private ComputerMBean()
+    {
+        List<MBeanAttributeInfo> attributes = new ArrayList<>();
+        for( Map.Entry<String, TrackingField> field : TrackingField.fields().entrySet() )
+        {
+            if( SKIP.contains( field.getValue() ) ) continue;
+
+            String name = CaseFormat.LOWER_UNDERSCORE.to( CaseFormat.LOWER_CAMEL, field.getKey() );
+            add( name, field.getValue(), attributes, null );
+        }
+
+        add( "task", TrackingField.TOTAL_TIME, attributes, TrackingField.TASKS );
+        add( "serverTask", TrackingField.SERVER_TIME, attributes, TrackingField.SERVER_COUNT );
+
+        this.info = new MBeanInfo(
+            ComputerMBean.class.getSimpleName(),
+            "metrics about all computers on the server",
+            attributes.toArray( new MBeanAttributeInfo[0] ), null, null, null
+        );
+    }
+
+    public static void register()
+    {
+        try
+        {
+            ManagementFactory.getPlatformMBeanServer().registerMBean( instance = new ComputerMBean(), new ObjectName( "dan200.computercraft:type=Computers" ) );
+        }
+        catch( InstanceAlreadyExistsException | MBeanRegistrationException | NotCompliantMBeanException | MalformedObjectNameException e )
+        {
+            ComputerCraft.log.warn( "Failed to register JMX bean", e );
+        }
+    }
+
+    public static void registerTracker()
+    {
+        if( instance != null ) Tracking.add( instance );
+    }
+
+    @Override
+    public Object getAttribute( String attribute ) throws AttributeNotFoundException, MBeanException, ReflectionException
+    {
+        LongSupplier value = attributes.get( attribute );
+        if( value == null ) throw new AttributeNotFoundException();
+        return value.getAsLong();
+    }
+
+    @Override
+    public void setAttribute( Attribute attribute ) throws InvalidAttributeValueException
+    {
+        throw new InvalidAttributeValueException( "Cannot set attribute" );
+    }
+
+    @Override
+    public AttributeList getAttributes( String[] attributes )
+    {
+        return null;
+    }
+
+    @Override
+    public AttributeList setAttributes( AttributeList attributes )
+    {
+        return new AttributeList();
+    }
+
+    @Override
+    public Object invoke( String actionName, Object[] params, String[] signature ) throws MBeanException, ReflectionException
+    {
+        return null;
+    }
+
+    @Override
+    @Nonnull
+    public MBeanInfo getMBeanInfo()
+    {
+        return info;
+    }
+
+    @Override
+    public void addTaskTiming( Computer computer, long time )
+    {
+        addValue( computer, TrackingField.TOTAL_TIME, time );
+    }
+
+    @Override
+    public void addServerTiming( Computer computer, long time )
+    {
+        addValue( computer, TrackingField.SERVER_TIME, time );
+    }
+
+    @Override
+    public void addValue( Computer computer, TrackingField field, long change )
+    {
+        Counter counter = values.get( field );
+        counter.value.addAndGet( change );
+        counter.count.incrementAndGet();
+    }
+
+    private MBeanAttributeInfo addAttribute( String name, String description, LongSupplier value )
+    {
+        attributes.put( name, value );
+        return new MBeanAttributeInfo( name, "long", description, true, false, false );
+    }
+
+    private void add( String name, TrackingField field, List<MBeanAttributeInfo> attributes, TrackingField count )
+    {
+        Counter counter = new Counter();
+        values.put( field, counter );
+
+        String prettyName = LanguageMap.getInstance().getOrDefault( field.translationKey() );
+        attributes.add( addAttribute( name, prettyName, counter.value::longValue ) );
+        if( count != null )
+        {
+            String countName = LanguageMap.getInstance().getOrDefault( count.translationKey() );
+            attributes.add( addAttribute( name + "Count", countName, counter.count::longValue ) );
+        }
+    }
+
+    private static class Counter
+    {
+        AtomicLong value = new AtomicLong();
+        AtomicLong count = new AtomicLong();
+    }
+}

src/main/java/dan200/computercraft/shared/proxy/ComputerCraftProxyCommon.java

@@ -11,6 +11,7 @@ import dan200.computercraft.api.media.IMedia;
 import dan200.computercraft.api.network.wired.IWiredElement;
 import dan200.computercraft.api.peripheral.IPeripheral;
 import dan200.computercraft.core.computer.MainThread;
+import dan200.computercraft.core.tracking.ComputerMBean;
 import dan200.computercraft.core.tracking.Tracking;
 import dan200.computercraft.shared.command.CommandComputerCraft;
 import dan200.computercraft.shared.command.arguments.ArgumentSerializers;
@@ -32,6 +33,8 @@ import net.minecraft.inventory.container.Container;
 import net.minecraft.item.Item;
 import net.minecraft.item.MusicDiscItem;
 import net.minecraft.loot.*;
+import net.minecraft.server.MinecraftServer;
+import net.minecraft.server.dedicated.DedicatedServer;
 import net.minecraft.util.ResourceLocation;
 import net.minecraft.util.registry.Registry;
 import net.minecraftforge.common.capabilities.CapabilityManager;
@@ -46,6 +49,7 @@ import net.minecraftforge.fml.DeferredWorkQueue;
 import net.minecraftforge.fml.common.Mod;
 import net.minecraftforge.fml.event.lifecycle.FMLCommonSetupEvent;
 import net.minecraftforge.fml.event.server.FMLServerStartedEvent;
+import net.minecraftforge.fml.event.server.FMLServerStartingEvent;
 import net.minecraftforge.fml.event.server.FMLServerStoppedEvent;
 import net.minecraftforge.items.CapabilityItemHandler;
 
@@ -161,12 +165,23 @@ public final class ComputerCraftProxyCommon
             CommandComputerCraft.register( event.getDispatcher() );
         }
 
+        @SubscribeEvent
+        public static void onServerStarting( FMLServerStartingEvent event )
+        {
+            MinecraftServer server = event.getServer();
+            if( server instanceof DedicatedServer && ((DedicatedServer) server).getProperties().enableJmxMonitoring )
+            {
+                ComputerMBean.register();
+            }
+        }
+
         @SubscribeEvent
         public static void onServerStarted( FMLServerStartedEvent event )
         {
             ComputerCraft.serverComputerRegistry.reset();
             WirelessNetwork.resetNetworks();
             Tracking.reset();
+            ComputerMBean.registerTracker();
         }
 
         @SubscribeEvent