The COM+ 1.5 Explorer lets you disable applications and components. When you disable an application, all client attempts to create any component from that application fail, and the following message is associated with the HRESULT: “The component has been disabled.” To disable an application, display its pop-up context menu and select Disable. A disabled application has a red square on it (like a player’s Stop button) in the COM+ 1.5 Explorer (see Figure B-5). To enable a disabled application, bring up the context menu again and select Enable. You can only disable a COM+ 1.5 application. Legacy applications cannot be disabled. Interestingly, a client that already has a reference to a COM+ object is not affected by the disabled application. Only clients that try to create new objects are affected. Consequently, you can have a disabled application running indefinitely.

Figure B-5. Disabling or enabling a COM+ 1.5 application from its pop-up context menu

You can also disable on a component-by-component basis instead of disabling an entire application. Every component pop-up context menu has a Disable option. Like a disabled application, a disabled component has a red square on it. All client attempts to create a disabled component fail, and the following message is associated with the HRESULT: “The component has been disabled.” You can disable any component in a COM+ 1.5 application, including legacy components (see Figure B-4). To enable a component, select Enable from its context menu. Like a disabled application, a disabled component only affects new activation requests. Existing references to objects are not affected. Enabled status for applications and components is stored in the COM+ Catalog and is therefore maintained between machine reboots.

Disabling applications or components is useful in two cases. The first situation is when you want to gracefully shut down an application on a live server machine to perform maintenance or upgrades. If you simply shut down the application, you might cause failures on client machines holding existing references. By disabling an application, you can have existing clients finish their work, while new activations may be routed to another machine, providing you the opportunity to perform maintenance. The other situation in which disabling an application is useful is during development and testing. It provides a guaranteed way to fail client calls and is thus a way to test your client-side error handling.

Currently, the COM+ Catalog interface ICOMAdminCatalog2 does not have methods used to programmatically disable or enable an application, but that situation could change by release time. Another possibility is that every COM+ application catalog object will have an Enabled named property. Currently, an application object has a Boolean property called IsEnabled that is set to TRUE if the application is enabled and FALSE if it is disabled. Similarity, components today do not have an Enabled named property, only a Boolean property called IsEnabled, used the same way as in the application object.