Pool Manager Sample Application (Pmgr_Svr.vp and Pmgr_Cli.vbp), Enterprise Edition

This sample app is an example of a simple pool manager that could be used to maintain open instances of Automation servers for client applications. Using this scheme, client applications ask the pool manager for a pointer to an object they want to use. The pool manager checks the pool, and either grants or denies the request. This approach has a number of benefits:

It avoids the lengthy Automation server creation costs associated with each client request. This is because the pool is typically created before a client needs a server.
Based on the frequency of client requests, the potential number of clients, and the duration of server tasks, a pool size can be created (or even adjusted as demand dictates at various times) that is significantly smaller than a one-to-one allocation scheme for clients and servers. For example: if the number of clients is 60, the average frequency of requests is one per minute per client, and the average duration of a server task is one second. A linear allocation plan would suggest that one server is needed to meet the needs of 60 clients. Realistically, requests will not be perfectly spaced; therefore, a reasonable level of redundancy, for instance a pool size of 5 Automation servers, could be used to meet the normal needs of the 60 clients.
It limits the number of servers that can be created of a specific type to a threshold that has been determined by the server administrator. This can be a very useful tuning parameter, and can also be useful in preventing the server from being abused by a peak request of a low priority server.

The server in this project uses a visible form purely for demonstration purposes. There is no functional need for the server to have any UI, though state information presented through a UI can help with debugging or run-time monitoring needs. (State monitoring requirements can also be addressed by providing a status method on the server that can be queried by a monitor application.)

File	Description
Pmgr_cli.vbp	Client component project file.
Pmgr_cli.frm	Client main form.
Pmgr_svr.vbp	Server component project file.
Pmgr_svr.frm	Server status indicator form.
Pmgr_svr.bas	Server main/global utility module.
Pmgr_svr.cls	Server class module.
Poolmngr.txt	A text file containing a project overview and description.

To Run

From the Visual Basic File menu, choose Open Project and select the Pmgr_svr.vbp file, which is listed in the Samples directory. Press F5 or choose Start from the Run menu to run the server project.

Once running, this project temporarily registers its classes in the system registry. You can then start a second instance of Visual Basic to run Pmgr_cli.vbp, the client that uses the class modules defined in Pmgr_svr.vbp.

Note The Automation server can be run on the same machine as the client, or it can be run on a remote machine to benefit from distributed processing power and support multi-user access. The Automation server does not need to be recompiled or changed in any way to support this location independence.