Agent Entry Points

Developing a VCS agent requires using the agent framework and implementing entry points. An entry point is a plug-in, defined by the user, that is called when an event, such as onlining, offlining, or monitoring a resource, occurs within the VCS agent. Definitions of each of the supported entry points begin with Agent Entry Points.

The VCS agent framework ensures that a resource has only one entry point running at a time. If multiple requests or events are received for the same resource, they are queued, then processed one at a time. An exception to this behavior is an optimization such that the agent framework discards internally generated periodic monitoring requests for a resource that is being monitored or that has a pending monitor request. However, because the agent framework is multithreaded, a single agent process can run entry points of several resources simultaneously. For example, if a resource receives requests to offline first, then close, the offline entry point is called first. The close entry point is called only after the offline request returns or times out. However, if the offline request is received for one resource, and the close request is received for another, both are called simultaneously.