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Introduction to the PostMaster


Caution!

The PostMaster was originally designed and implemented for integrating tools in the SDL Suite environment. Currently it integrates tools in the SDL Suite and the TTCN Suite environment. Our experience is that the PostMaster is also suitable for integrating external tools and applications with SDL Suite or TTCN Suite applications; one application area is for instance quick prototyping.

However, IBM Rational does not support using the PostMaster as a communication mechanism between real-time applications, in a run-time environment.

The PostMaster is the mechanism used for communication between the different tools in SDL Suite and TTCN Suite. A C program generated by the SDL Suite or the TTCN Suite tools can also take advantage of this communication mechanism. It can communicate with any application connected to the PostMaster that send messages according to a defined format. This makes it possible for an SDL simulator to communicate with, for instance, a user interface process for the Simulator.

The PostMaster also provides the basic means for an open public interface concept, see The Public Interface.

The PostMaster provides the following functionality:

The PostMaster is a message passing service based on a selective broadcasting mechanism. It will distribute a copy of each message it receives to the tools subscribing to that type of message. By this, the PostMaster provides an integration mechanism between tools without the hard coupling between them that follows from conventional two part communication mechanisms.

Figure 159 illustrates some of the PostMaster concepts. The PostMaster maintains a list of which messages each tool subscribes to. Each tool has a PostMaster part for sending and receiving messages. In the figure, tool F broadcasts a message, i.e. the message is sent to the PostMaster. The subscription lists of tool A and C (but not the lists of B and F) contains the message type. Accordingly the PostMaster broadcasts the message to tool A and C.

Figure 159 : Example of a PostMaster broadcast

The PostMaster configuration is a file that informs the PostMaster about what tools and messages exist in the current context, i.e. it contains the message subscription lists. To include new tools or add new messages, the configuration must be edited.

For detailed information on the configuration, see The PostMaster Configuration.


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