Thursday, July 9, 2009

C++/Java Invocation API: Java App Meets Vista Logo Certification?

Attachmate wanted to prepare an update to their Windows-native product, Reflection X, in Java so it could be run on several previously unsupported operating systems. At the same time, another significant goal was supplied from Attachmate's Marketing department, which specified that Reflection X must pass Microsoft's Vista Logo Certification.

Vista Logo requires a candidate application to meet more than 30 Microsoft-specified requirements that are to be tested by a third party validator, in this case Veri-Test. Two items from the list of requirements are 1) the application must provide a fully capable MSI installer; and 2) the application must conform to the Windows Error Reporting (WER) initiative. In a nutshell, the WER requirement will be met when 1) serious runtime exceptions are recognized by the application; 2) the user is warned via a common Windows dialog that asks if the problem should be reported to Microsoft; 3) if the user selects OK, a minidump is transmitted to the Microsoft WER site where it can be bucketed for statistical purposes and from where the user can be redirected to a website that provides further information on a workaround or product update; & 4) an application restart action can be started.

I prepared a WIX MSI installer that installed the Reflection X jar files, documents, graphic images, language resources, and JVM, and then installed and started the Reflection X Server, the underlying Windows service. Difficulty with the WER requirement came from the fact that the Java JVM is a virtual machine that contains its internal threads within structured exception handlers (SEH). That means that any serious or fatal Java exception that originates in Reflection X -- the kind that should be reported via the WER -- would be caught by the JVM, never making its way to a WER handler in RX's Java launcher application.

The interesting solution to this problem was found in the precedence given to different exception handler types. As mentioned above, a SEH is defined to surround each Java thread and therefore catches all exceptions that originate within the thread. If an exception is not handled in an application's SEH then the JVM will eventually catch it with one of its own handlers, ensuring that none escape to an interested WER manager. Another exception type, a Vectored Exception Handler (VEH), is given the first look at every exception thrown within the application by the operating sytem before it makes it to any SEH. I added a VEH to Reflection X's Java launcher application that evaluates every exception Reflection X generates and reports serious or fatal failures to the WER before passing them on to the SEH that should eventually handle it.

As a result of this design, and I think much to Microsoft's chagrin, Reflection X 2008 is the only Java application to earn Vista Logo Certification.

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