Add back executeMainThreadTask

Closes #868

src/main/java/dan200/computercraft/api/lua/ILuaContext.java

@@ -27,4 +27,18 @@ public interface ILuaContext
      * @see LuaFunction#mainThread() To run functions on the main thread and return their results synchronously.
      */
     long issueMainThreadTask( @Nonnull ILuaTask task ) throws LuaException;
+
+    /**
+     * Queue a task to be executed on the main server thread at the beginning of next tick, waiting for it to complete.
+     * This should be used when you need to interact with the world in a thread-safe manner.
+     *
+     * Note that the return values of your task are handled as events, meaning more complex objects such as maps or
+     * {@link IDynamicLuaObject} will not preserve their identities.
+     *
+     * @param task The task to execute on the main thread.
+     * @return The objects returned by {@code task}.
+     * @throws LuaException If the task could not be queued, or if the task threw an exception.
+     */
+    @Nonnull
+    MethodResult executeMainThreadTask( @Nonnull ILuaTask task ) throws LuaException;
 }

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

@@ -9,6 +9,8 @@ import dan200.computercraft.ComputerCraft;
 import dan200.computercraft.api.lua.ILuaContext;
 import dan200.computercraft.api.lua.ILuaTask;
 import dan200.computercraft.api.lua.LuaException;
+import dan200.computercraft.api.lua.MethodResult;
+import dan200.computercraft.core.asm.TaskCallback;
 import dan200.computercraft.core.computer.Computer;
 import dan200.computercraft.core.computer.MainThread;
 
@@ -66,4 +68,11 @@ class LuaContext implements ILuaContext
             throw new LuaException( "Task limit exceeded" );
         }
     }
+
+    @Nonnull
+    @Override
+    public MethodResult executeMainThreadTask( @Nonnull ILuaTask task ) throws LuaException
+    {
+        return TaskCallback.make( this, task );
+    }
 }

src/test/java/dan200/computercraft/core/apis/ObjectWrapper.java

@@ -8,6 +8,7 @@ package dan200.computercraft.core.apis;
 import dan200.computercraft.api.lua.*;
 import dan200.computercraft.core.asm.LuaMethod;
 import dan200.computercraft.core.asm.NamedMethod;
+import dan200.computercraft.core.asm.TaskCallback;
 
 import javax.annotation.Nonnull;
 import java.util.HashMap;
@@ -64,4 +65,11 @@ public class ObjectWrapper implements ILuaContext
     {
         throw new IllegalStateException( "Method should never queue events" );
     }
+
+    @Nonnull
+    @Override
+    public MethodResult executeMainThreadTask( @Nonnull ILuaTask task ) throws LuaException
+    {
+        return TaskCallback.make( this, task );
+    }
 }

src/test/java/dan200/computercraft/core/asm/GeneratorTest.java

@@ -11,6 +11,7 @@ import dan200.computercraft.core.computer.ComputerSide;
 import org.hamcrest.Matcher;
 import org.junit.jupiter.api.Test;
 
+import javax.annotation.Nonnull;
 import java.io.IOException;
 import java.util.Collection;
 import java.util.List;
@@ -248,5 +249,19 @@ public class GeneratorTest
         return contramap( is( method ), "name", NamedMethod::getName );
     }
 
-    private static final ILuaContext CONTEXT = task -> 0;
+    private static final ILuaContext CONTEXT = new ILuaContext()
+    {
+        @Override
+        public long issueMainThreadTask( @Nonnull ILuaTask task )
+        {
+            return 0;
+        }
+
+        @Nonnull
+        @Override
+        public MethodResult executeMainThreadTask( @Nonnull ILuaTask task ) throws LuaException
+        {
+            return TaskCallback.make( this, task );
+        }
+    };
 }