Being a highly customizable language and tool support development environment, MetaEdit+ may sometimes expose the end user to issues originating from the language or code generator definitions made by the metamodeler. We have done our best to prevent this from happening, but in order to retain the maximum expressive power for language development, the metamodeler is not actively prohibited from making mistakes such as destructive refactoring or implementing accidental infinite loops. Incomplete or erroneous language or generator definitions may result in run-time anomalies or erratic behavior. This is quite normal during the development stage of a new language, but sometimes such troubles may unfortunately slip through the metamodeler’s testing into deployment.

The most common case of an apparent hang is an infinite recursion in a generator. If this happens in a generator run automatically in the background (e.g. an identifier generator while displaying an object in a list, or a symbol’s text label generator while displaying a diagram), MetaEdit+ will cut the generation short at the timeout value specified in Options | System: see Section 3.1.3. The generation output so far will be shown, followed by ‘*Error*: Generator took too long - maybe recursion e.g. id; in identifier generator?’. Alternatively, if a manually started generator hangs, the user can press the Break button in the progress bar widget to interrupt the generator and open a Generator Debugger: see Section 5.2.1. The information in the Generator Debugger may be useful to the metamodeler; the modeler can continue work as normal.

Aside from bugs in generators or MetaEdit+ itself, trouble may also arise from corrupted model and repository data structures. Typical sources for corruption are power and hardware failures that may have left the repository in a faulty state, careless system administration operation, or metamodel or model imports. While MetaEdit+ can usually catch and prevent suspicious import operations, or can revert from them by abandoning the current transaction, there may arise a condition where MetaEdit+ shows an error dialog, hangs, or otherwise prevents further work. An error dialog looks like Figure 2–2:

The error dialog has buttons to Proceed with the current operation (if possible), Terminate it or Exit MetaEdit+. If you choose to terminate the operation, please note that the operation is left half-finished and it is not recommended to commit the current transaction unless you are completely sure that data integrity was not affected. Also please note that choosing Exit MetaEdit+ will initiate an emergency exit procedure which will automatically discard the changes made during the current transaction.

Whenever an error dialog is opened, MetaEdit+ will write a trace to the meplus0.err file in the current working directory; please include that file when reporting the problem to MetaCase.

If multiple error dialogs continue to open a few seconds apart, the problem is most likely an error in displaying the contents of a window. Minimize the application windows, Terminate the error dialogs, and restore the windows one at a time to find the offending window. Minimize that window again, choose Close from the operating system pop-up menu for the minimized window, and Terminate any error dialogs.

If MetaEdit+ hangs during an operation other than generation, the user can interrupt processing of the MetaEdit+ program itself by pressing F8, which will open an error dialog as above. In those cases when pressing F8 does not help or MetaEdit+ encounters an unrecoverable problem, an Emergency Evaluator (Figure 2–3) can be launched by pressing Shift+F8.

In the Emergency Evaluator the following operations are available by typing the respective command and pressing ESC:

If your MetaEdit+ license includes the API features, the following are also available:

Any valid command line parameter sequence is also supported with the API: see the ‘MetaEdit+ Workbench User’s Guide’ for available command line parameters and formatting (as for internal...execute in MERL).

Please note that the Emergency Evaluator is provided only as the last line of defense in those cases where work cannot be continued, or only at the risk of repository corruption. The evaluator provides minimal means for saving the current work and closing MetaEdit+ – it does not provide tools for debugging or repairing the underlying problem.