Correctly invalidate the ROM mount cache

Before it would remain the same across world reloads, and thus would be
out-of-date after leaving the first world. This architecture technically
allows for running multiple servers at once, though that's not going to
matter that soon.

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

@@ -6,11 +6,9 @@
 
 package dan200.computercraft;
 
-import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.turtle.event.TurtleAction;
 import dan200.computercraft.core.apis.AddressPredicate;
 import dan200.computercraft.core.apis.http.websocket.Websocket;
-import dan200.computercraft.core.filesystem.ResourceMount;
 import dan200.computercraft.shared.Config;
 import dan200.computercraft.shared.computer.blocks.BlockComputer;
 import dan200.computercraft.shared.computer.core.ClientComputerRegistry;
@@ -194,13 +192,6 @@ public static String getVersion()
         return "${version}";
     }
 
-    static IMount createResourceMount( String domain, String subPath )
-    {
-        IReloadableResourceManager manager = ServerLifecycleHooks.getCurrentServer().getResourceManager();
-        ResourceMount mount = new ResourceMount( domain, subPath, manager );
-        return mount.exists( "" ) ? mount : null;
-    }
-
     public static InputStream getResourceFile( String domain, String subPath )
     {
         IReloadableResourceManager manager = ServerLifecycleHooks.getCurrentServer().getResourceManager();

src/main/java/dan200/computercraft/ComputerCraftAPIImpl.java

@@ -6,6 +6,7 @@
 
 package dan200.computercraft;
 
+import com.google.common.collect.MapMaker;
 import dan200.computercraft.api.ComputerCraftAPI.IComputerCraftAPI;
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.api.filesystem.IWritableMount;
@@ -20,20 +21,26 @@
 import dan200.computercraft.api.turtle.ITurtleUpgrade;
 import dan200.computercraft.core.apis.ApiFactories;
 import dan200.computercraft.core.filesystem.FileMount;
+import dan200.computercraft.core.filesystem.ResourceMount;
 import dan200.computercraft.shared.*;
 import dan200.computercraft.shared.peripheral.modem.wireless.WirelessNetwork;
 import dan200.computercraft.shared.util.IDAssigner;
 import dan200.computercraft.shared.wired.CapabilityWiredElement;
 import dan200.computercraft.shared.wired.WiredNode;
+import net.minecraft.resources.IReloadableResourceManager;
 import net.minecraft.tileentity.TileEntity;
 import net.minecraft.util.Direction;
+import net.minecraft.util.ResourceLocation;
 import net.minecraft.util.math.BlockPos;
 import net.minecraft.world.IBlockReader;
 import net.minecraft.world.World;
 import net.minecraftforge.common.util.LazyOptional;
+import net.minecraftforge.fml.server.ServerLifecycleHooks;
 
 import javax.annotation.Nonnull;
 import java.io.File;
+import java.lang.ref.WeakReference;
+import java.util.Map;
 
 public final class ComputerCraftAPIImpl implements IComputerCraftAPI
 {
@@ -43,6 +50,9 @@ private ComputerCraftAPIImpl()
     {
     }
 
+    private WeakReference<IReloadableResourceManager> currentResources;
+    private final Map<ResourceLocation, ResourceMount> mountCache = new MapMaker().weakValues().concurrencyLevel( 1 ).makeMap();
+
     @Nonnull
     @Override
     public String getInstalledVersion()
@@ -72,7 +82,9 @@ public IWritableMount createSaveDirMount( @Nonnull World world, @Nonnull String
     @Override
     public IMount createResourceMount( @Nonnull String domain, @Nonnull String subPath )
     {
-        return ComputerCraft.createResourceMount( domain, subPath );
+        IReloadableResourceManager manager = ServerLifecycleHooks.getCurrentServer().getResourceManager();
+        ResourceMount mount = ResourceMount.get( domain, subPath, manager );
+        return mount.exists( "" ) ? mount : null;
     }
 
     @Override

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

@@ -56,9 +56,6 @@ final class ComputerExecutor
 {
     private static final int QUEUE_LIMIT = 256;
 
-    private static IMount romMount;
-    private static final Object romMountLock = new Object();
-
     private final Computer computer;
     private final List<ILuaAPI> apis = new ArrayList<>();
     final TimeoutState timeout = new TimeoutState();
@@ -329,16 +326,10 @@ void tick()
 
     private IMount getRomMount()
     {
-        if( romMount != null ) return romMount;
-
-        synchronized( romMountLock )
-        {
-            if( romMount != null ) return romMount;
-            return romMount = computer.getComputerEnvironment().createResourceMount( "computercraft", "lua/rom" );
-        }
+        return computer.getComputerEnvironment().createResourceMount( "computercraft", "lua/rom" );
     }
 
-    IWritableMount getRootMount()
+    private IWritableMount getRootMount()
     {
         if( rootMount == null )
         {

src/main/java/dan200/computercraft/core/filesystem/ResourceMount.java

@@ -8,13 +8,16 @@
 
 import com.google.common.cache.Cache;
 import com.google.common.cache.CacheBuilder;
+import com.google.common.collect.MapMaker;
 import com.google.common.io.ByteStreams;
+import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.filesystem.IMount;
 import dan200.computercraft.core.apis.handles.ArrayByteChannel;
 import net.minecraft.resources.IReloadableResourceManager;
 import net.minecraft.resources.IResource;
 import net.minecraft.resources.IResourceManager;
 import net.minecraft.util.ResourceLocation;
+import net.minecraft.util.ResourceLocationException;
 import net.minecraftforge.resource.IResourceType;
 import net.minecraftforge.resource.ISelectiveResourceReloadListener;
 
@@ -29,7 +32,7 @@
 import java.util.concurrent.TimeUnit;
 import java.util.function.Predicate;
 
-public class ResourceMount implements IMount
+public final class ResourceMount implements IMount
 {
     /**
      * Only cache files smaller than 1MiB.
@@ -55,6 +58,13 @@ public class ResourceMount implements IMount
         .<FileEntry, byte[]>weigher( ( k, v ) -> v.length )
         .build();
 
+    private static final MapMaker CACHE_TEMPLATE = new MapMaker().weakValues().concurrencyLevel( 1 );
+
+    /**
+     * Maintain a cache of currently loaded resource mounts. This cache is invalidated when currentManager changes.
+     */
+    private static final Map<IReloadableResourceManager, Map<ResourceLocation, ResourceMount>> MOUNT_CACHE = new WeakHashMap<>( 2 );
+
     private final String namespace;
     private final String subPath;
     private final IReloadableResourceManager manager;
@@ -62,7 +72,26 @@ public class ResourceMount implements IMount
     @Nullable
     private FileEntry root;
 
-    public ResourceMount( String namespace, String subPath, IReloadableResourceManager manager )
+    public static ResourceMount get( String namespace, String subPath, IReloadableResourceManager manager )
+    {
+        Map<ResourceLocation, ResourceMount> cache;
+
+        synchronized( MOUNT_CACHE )
+        {
+            cache = MOUNT_CACHE.get( manager );
+            if( cache == null ) MOUNT_CACHE.put( manager, cache = CACHE_TEMPLATE.makeMap() );
+        }
+
+        ResourceLocation path = new ResourceLocation( namespace, subPath );
+        synchronized( cache )
+        {
+            ResourceMount mount = cache.get( path );
+            if( mount == null ) cache.put( path, mount = new ResourceMount( namespace, subPath, manager ) );
+            return mount;
+        }
+    }
+
+    private ResourceMount( String namespace, String subPath, IReloadableResourceManager manager )
     {
         this.namespace = namespace;
         this.subPath = subPath;
@@ -119,7 +148,17 @@ private void create( FileEntry lastEntry, String path )
             FileEntry nextEntry = lastEntry.children.get( part );
             if( nextEntry == null )
             {
-                lastEntry.children.put( part, nextEntry = new FileEntry( new ResourceLocation( namespace, subPath + "/" + path ) ) );
+                ResourceLocation childPath;
+                try
+                {
+                    childPath = new ResourceLocation( namespace, subPath + "/" + path );
+                }
+                catch( ResourceLocationException e )
+                {
+                    ComputerCraft.log.warn( "Cannot create resource location for {} ({})", part, e.getMessage() );
+                    return;
+                }
+                lastEntry.children.put( part, nextEntry = new FileEntry( childPath ) );
             }
 
             lastEntry = nextEntry;

src/test/java/dan200/computercraft/core/filesystem/ResourceMountTest.java

@@ -31,7 +31,7 @@ public void before()
         SimpleReloadableResourceManager manager = new SimpleReloadableResourceManager( ResourcePackType.SERVER_DATA, null );
         manager.addResourcePack( new FolderPack( new File( "src/main/resources" ) ) );
 
-        mount = new ResourceMount( "computercraft", "lua/rom", manager );
+        mount = ResourceMount.get( "computercraft", "lua/rom", manager );
     }
 
     @Test