Shut down computers on errors

Previously we would attempt to resume them, which then caused confusing
behaviour if the Lua VM was in an inconsistent state.

Closes #811

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

@@ -251,6 +251,20 @@ void queueStop( boolean reboot, boolean close )
      * and then schedule a shutdown.
      */
     void abort()
+    {
+        immediateFail( StateCommand.ABORT );
+    }
+
+    /**
+     * Abort this whole computer due to an internal error. This will immediately destroy the Lua machine,
+     * and then schedule a shutdown.
+     */
+    void fastFail()
+    {
+        immediateFail( StateCommand.ERROR );
+    }
+
+    private void immediateFail( StateCommand command )
     {
         ILuaMachine machine = this.machine;
         if( machine != null ) machine.close();
@@ -258,7 +272,7 @@ void abort()
         synchronized( queueLock )
         {
             if( closed ) return;
-            command = StateCommand.ABORT;
+            this.command = command;
             if( isOn ) enqueue();
         }
     }
@@ -596,6 +610,12 @@ void work() throws InterruptedException
                     displayFailure( "Error running computer", TimeoutState.ABORT_MESSAGE );
                     shutdown();
                     break;
+
+                case ERROR:
+                    if( !isOn ) return;
+                    displayFailure( "Error running computer", "An internal error occurred, see logs." );
+                    shutdown();
+                    break;
             }
         }
         else if( event != null )
@@ -644,6 +664,7 @@ private enum StateCommand
         SHUTDOWN,
         REBOOT,
         ABORT,
+        ERROR,
     }
 
     private static final class Event

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

@@ -506,6 +506,8 @@ public void run()
                 catch( Exception | LinkageError | VirtualMachineError e )
                 {
                     ComputerCraft.log.error( "Error running task on computer #" + executor.getComputer().getID(), e );
+                    // Tear down the computer immediately. There's no guarantee it's well behaved from now on.
+                    executor.fastFail();
                 }
                 finally
                 {