Put some limits on various external queues

Ideally turtle functions would error, but wrangling that is more pain
than it's worth.

config/checkstyle/suppressions.xml

@@ -7,9 +7,6 @@
     <suppress checks="StaticVariableName" files=".*[\\/]ComputerCraft.java" />
     <suppress checks="StaticVariableName" files=".*[\\/]ComputerCraftAPI.java" />
 
-    <!-- Do not check for missing package Javadoc. -->
-    <suppress checks="JavadocStyle" files=".*[\\/]package-info.java" />
-
     <!-- The commands API is documented in Lua. -->
     <suppress checks="SummaryJavadocCheck" files=".*[\\/]CommandAPI.java" />
 </suppressions>

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

@@ -37,7 +37,7 @@ public class HTTPAPI implements ILuaAPI
 {
     private final IAPIEnvironment apiEnvironment;
 
-    private final ResourceGroup<CheckUrl> checkUrls = new ResourceGroup<>();
+    private final ResourceGroup<CheckUrl> checkUrls = new ResourceGroup<>( ResourceGroup.DEFAULT );
     private final ResourceGroup<HttpRequest> requests = new ResourceQueue<>( () -> ComputerCraft.httpMaxRequests );
     private final ResourceGroup<Websocket> websockets = new ResourceGroup<>( () -> ComputerCraft.httpMaxWebsockets );
 
@@ -127,7 +127,10 @@ public final Object[] request( IArguments args ) throws LuaException
             HttpRequest request = new HttpRequest( requests, apiEnvironment, address, postString, headers, binary, redirect );
 
             // Make the request
-            request.queue( r -> r.request( uri, httpMethod ) );
+            if( !request.queue( r -> r.request( uri, httpMethod ) ) )
+            {
+                throw new LuaException( "Too many ongoing HTTP requests" );
+            }
 
             return new Object[] { true };
         }
@@ -138,12 +141,15 @@ public final Object[] request( IArguments args ) throws LuaException
     }
 
     @LuaFunction
-    public final Object[] checkURL( String address )
+    public final Object[] checkURL( String address ) throws LuaException
     {
         try
         {
             URI uri = HttpRequest.checkUri( address );
-            new CheckUrl( checkUrls, apiEnvironment, address, uri ).queue( CheckUrl::run );
+            if( !new CheckUrl( checkUrls, apiEnvironment, address, uri ).queue( CheckUrl::run ) )
+            {
+                throw new LuaException( "Too many ongoing checkUrl calls" );
+            }
 
             return new Object[] { true };
         }

src/main/java/dan200/computercraft/core/apis/http/Resource.java

@@ -97,7 +97,7 @@ public final void close()
         tryClose();
     }
 
-    public boolean queue( Consumer<T> task )
+    public final boolean queue( Consumer<T> task )
     {
         @SuppressWarnings( "unchecked" )
         T thisT = (T) this;

src/main/java/dan200/computercraft/core/apis/http/ResourceGroup.java

@@ -18,6 +18,9 @@
  */
 public class ResourceGroup<T extends Resource<T>>
 {
+    public static final int DEFAULT_LIMIT = 512;
+    public static final IntSupplier DEFAULT = () -> DEFAULT_LIMIT;
+
     private static final IntSupplier ZERO = () -> 0;
 
     final IntSupplier limit;

src/main/java/dan200/computercraft/core/apis/http/ResourceQueue.java

@@ -38,8 +38,10 @@ public synchronized void shutdown()
     public synchronized boolean queue( Supplier<T> resource )
     {
         if( !active ) return false;
+        if( super.queue( resource ) ) return true;
+        if( pending.size() > DEFAULT_LIMIT ) return false;
 
-        if( !super.queue( resource ) ) pending.add( resource );
+        pending.add( resource );
         return true;
     }
 

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

@@ -503,20 +503,15 @@ public void addFuel( int fuel )
         setFuelLevel( getFuelLevel() + addition );
     }
 
-    private int issueCommand( ITurtleCommand command )
-    {
-        commandQueue.offer( new TurtleCommandQueueEntry( ++commandsIssued, command ) );
-        return commandsIssued;
-    }
-
     @Nonnull
     @Override
     public MethodResult executeCommand( @Nonnull ITurtleCommand command )
     {
         if( getWorld().isClientSide ) throw new UnsupportedOperationException( "Cannot run commands on the client" );
+        if( commandQueue.size() > 16 ) return MethodResult.of( false, "Too many ongoing turtle commands" );
 
-        // Issue command
-        int commandID = issueCommand( command );
+        commandQueue.offer( new TurtleCommandQueueEntry( ++commandsIssued, command ) );
+        int commandID = commandsIssued;
         return new CommandCallback( commandID ).pull;
     }