ToolTalk messages contain attributes that store message information and provide delivery information to the ToolTalk service. This delivery information is used to route the messages to the appropriate receivers.
ToolTalk messages are simple structures that contain attributes for address, subject (such as operation and arguments), and delivery information (such as class and scope.) Each message contains attributes from .
Table 8-1 ToolTalk Message Attributes
Messages addressed to other applications can be addressed to a particular process or to any process that has registered a pattern that matches your message. When you address a message to a process, you need to know the process identifier (procid) of the other application. However, processes do not usually know each other's procid; more often, a sender does not care which process performs an operation (request message) or learns of an event (notice message).
Applications that use the ToolTalk service to communicate usually have something in common – the applications are running in the same session, or they are interested in the same file or data. To register this interest, applications join sessions or files (or both) with the ToolTalk service. This file and session information is used by the ToolTalk service with the message patterns to determine which applications should receive a message.
Note - The scope attributes are restricted to NFS and UFS files systems; file scoping does not work across file systems (for example, a tmpfs file system.)
When a message is scoped to a file, only those applications that have joined the file (and match the remaining attributes) will receive the message. Applications that share interest in a file do not have to be running in the same session.
Table 8-2 Scoping a Message with Patterns to a File
Example 8-1 Scoping to Union of TT_FILE_IN_SESSION and TT_SESSION
Messages have the same types of file-based scoping mechanisms as patterns. describes these scopes.
Table 8-3 Scoping Mechanisms for Messages
When a message is scoped to TT_FILE or TT_BOTH, the ToolTalk client library checks the database server for all sessions that have clients that are interested in the file and sends the message to all of the interested ToolTalk sessions. The ToolTalk sessions then match the messages to the appropriate clients. The message sender is not required to explicitly call to tt_file_join.
If a message that is scoped to TT_FILE_IN_SESSION or TT_SESSION contains a file, the database server is not contacted and the message is sent only to clients that are scoped to the message's session.
When a message is scoped to a session, only those applications that have connected to that session are considered as potential recipients.
Example 8-2 Setting a Session
The first line creates message. The second line adds scope to message, and the last line adds file attribute that does not affect message scope.
Applications can be very specific about the distribution of a message by specifying TT_FILE_IN_SESSION for the message scope. Only those applications that have joined both the file and the session indicated are considered potential recipients.
Applications can also scope a message to every client that has registered interest in the message's session by specifying TT_SESSION with tt_message_file_set for the message scope. When the message is received by a client whose pattern matches, the receiving client can get the file name by calling tt_message_file.
Example 8-3 Setting a File
The first line creates message. The second line adds scope. The third line adds file to message scope.
The ToolTalk service supports three types of data for message arguments: integers, null-terminated strings, and byte strings.
To send any other data type in a ToolTalk message, the client must serialize the data into a string or byte string and then deserialize it on receipt. The new XDR argument API calls provided with the ToolTalk service now handles these serialization and deserialization functions. The client only needs to provide an XDR routine and a pointer to the data. After serializing the data into the internal buffer, the ToolTalk service treats the data in the same manner as it treats a byte stream.