COM & .NET Component Services

Queued Components Architecture

One of the major requirements for the COM+ queued components architecture specifies that the component developer should take no special steps to make a component asynchronous; the developer writes synchronous code, and COM+ provides the mechanism to allow clients to call the method asynchronously.

As a result, the client cannot create the component directly, since it would result in the usual blocking calls. Instead, COM+ uses the architecture shown in Figure 8-1. For every queued component, COM+ provides a recorder object. The recorder object supports the same set of interfaces as the queued component. When the client calls methods on the recorder interfaces (Step 1), the recorder (as the name implies) merely records the calls. When the client releases the recorder, the recorder converts the calls to an MSMQ message and posts that message to the recorder queue (Step 2).

Every application that contains queued components has a queue associated with it. MSMQ transfers the message to the application queue from the recorder queue (Step 3). For each application, COM+ maintains a listener object that detects when a message was added to the application queue (Step 4). The listener creates a player object (Step 5) and instructs it to retrieve the message from the queue (Step 6). The player creates the actual component and plays the calls back to it (Step 7). When the player is finished playing back calls, it releases the component.

Figure 8-1.  COM+ queued ...