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OOMMF Architecture Overview

Before describing each of the applications which comprise the OOMMF software, it is helpful to understand how these applications work together. OOMMF is not structured as a single program. Instead it is a collection of programs, each specializing in some task needed as part of a micromagnetic simulation system. An advantage of this modular architecture is that each program may be improved or even replaced without a need to redesign the entire system.

The OOMMF programs work together by providing services to one another. The programs communicate over Internet (TCP/IP) connections, even when the programs are running on a common host. An advantage of this design is that distributed operation of OOMMF programs over a networked collection of hosts is supported in the basic design, though it is not fully realized in the current release.

When two OOMMF applications are in the relationship that one is requesting a service from the other, it is convenient to introduce some clarifying terminology. Let us refer to the application that is providing a service as the ``server application'' and the application requesting the service as the ``client application.'' Note that a single application can be both a server application in one service relationship and a client application in another service relationship.

Each server application provides its service on a particular Internet port, and needs to inform potential client applications how to obtain its service. Each client application needs to be able to look up possible providers of the service it needs. The intermediary which brings server applications and client applications together is another application called the ``account service directory.'' There may be at most one account service directory application running under the user ID of each user account on a host. Each account service directory keeps track of all the services provided by OOMMF server applications running under its user account on its host and the corresponding Internet ports at which those services may be obtained. OOMMF server applications register their services with the corresponding account service directory application. OOMMF client applications look up service providers running under a particular user ID in the corresponding account server directory application.

The account service directory applications simplify the problem of matching servers and clients, but they do not completely solve it. OOMMF applications still need a mechanism to find out how to obtain the service of the account service directory! Another application, called the ``host service directory'' serves this function. Only one copy of the host service directory application runs on each host. Its sole purpose is to tell OOMMF applications where to obtain the services of account service directories on that host. Because only one copy of this application runs per host, it can provide its service on a well-known port which is configured into the OOMMF software. By default, this is port 15136. OOMMF software can be customized to use a different port number.

The account service directory applications perform another task as well. They launch other programs under the user ID for which they manage service registration. The user controls the launching of programs through the interface provided by the application mmLaunch, but it is the account service directory application that actually spawns a subprocess for the new application. Because of this architecture, most OOMMF applications are launched as child processes of an account service directory application. These child processes inherit their environment from their parent account service directory application, including their working directory, and other key environment variables, such as DISPLAY. Each account service directory application sets its working directory to the root directory of the OOMMF distribution.

These service directory applications are vitally important to the operation of the total OOMMF micromagnetic simulation system. However, it would be easy to overlook them. They act entirely ``behind the scenes'' without a user interface window. Furthermore, they are never launched by the user. When any server application needs to register its service, if it finds that these service directory applications are not running, it launches new copies of them. In this way the user can be sure that if any OOMMF server applications are running, then so are the service directory applications needed to direct clients to its service. After all server applications terminate, and there are no longer any services registered with a service directory application, it terminates as well. Similarly, when all service directory applications terminate, the host service directory application exits.

In the sections which follow, the OOMMF applications are described in terms of the services they provide and the services they require.

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OOMMF Documentation Team
May 11, 2021