ToolTalk Message Distribution

The ToolTalk service provides two methods of addressing messages: process-oriented messages and object-oriented messages.

Process-Oriented Messages

Process-oriented messages are addressed to processes. Applications that create a process-oriented message address the message to either a specific process or to a particular type of process. Process-oriented messages are a good way for existing applications to begin communication with other applications. Modifications to support process-oriented messages are straightforward and usually take a short time to implement.

Object-Oriented Messages

Object-oriented messages are addressed to objects managed by applications. Applications that create an object-oriented message address the message to either a specific object or to a particular type of object. Object-oriented messages are particularly useful for applications that currently use objects or that are to be designed around objects. If an existing application is not object-oriented, the ToolTalk service allows applications to identify portions of application data as objects so that applications can begin to communicate about these objects.

Programs coded to the ToolTalk object-oriented messaging interface are not portable to CORBA-compliant systems without source changes.

Determining Message Delivery

To determine which groups receive messages, you scope your messages. Scoping limits the delivery of messages to a particular session or file.

Sessions

A session is a group of processes that have an instance of the ToolTalk message server in common. When a process opens communication with the ToolTalk service, a default session is located (or created if a session does not already exist) and a process identifier (procid) is assigned to the process. Default sessions are located either through an environment variable (called process tree sessions) or through the X display (called X sessions).

The concept of a session is important in the delivery of messages. Senders can scope a message to a session and the ToolTalk service will deliver it to all processes that have message patterns that reference the current session. To update message patterns with the current session identifier (sessid), applications join the session.

Files

A container for data that is of interest to applications is called a file in this book.

The concept of a file is important in the delivery of messages. Senders can scope a message to a file and the ToolTalk service will deliver it to all processes that have message patterns that reference the file without regard to the process's default session. To update message patterns with the current file path name, applications join the file.

You can also scope a message to a file within a session. The ToolTalk service will deliver the message to all processes that reference both the file and session in their message patterns.

The file scoping feature is restricted to NFS and UFS file systems; it does not work, for example, across tmpfs filesystems.