Participating in ToolTalk Sessions

This chapter provides instructions on how to participate in a ToolTalk session. It also shows you how to manage storage of values passed in from the ToolTalk service and how to handle errors that the ToolTalk service returns.

To use the ToolTalk service, your application calls ToolTalk functions from the ToolTalk API library. To modify your application to use the ToolTalk service, you must first include the ToolTalk API header file in your program. After you have initialized the ToolTalk service and joined a session, you can join files and additional user sessions. When your process is ready to quit, you unregister your message patterns and leave your ToolTalk session.

Including the ToolTalk API Header File

To modify your application to use the ToolTalk service, first you must include the ToolTalk API header file tt_c.h in your program. This file resides in the /usr/dt/include/Tt/ directory.

The following code sample shows how a program includes this file.

#include <stdio.h>
#include <sys/param.h>
#include <sys/types.h>
#include <Tt/tt_c.h>

Registering with the ToolTalk Service

Before you can participate in ToolTalk sessions, you must register your process with the ToolTalk service. You can either register in the ToolTalk session in which the application was started (the initial session), or locate another session and register there.

The ToolTalk functions you need to register with the ToolTalk service are shown in Table 7-1.

Table 7-1 Registering with the ToolTalk Service

Registering in the Initial Session

To initialize and register your process with the initial ToolTalk session, your application needs to obtain a process identifier (procid). You can then obtain the file descriptor (fd) that corresponds to the newly initialized ToolTalk process.

The following code sample first initializes and registers the sample program with the ToolTalk service, and then obtains the corresponding file descriptor.

int ttfd;
char   *my_procid;

/*
 * Initialize ToolTalk, using the initial default session
 */

my_procid = tt_open();

/*
 * obtain the file descriptor that will become active whenever
 * ToolTalk has a message for this process.
 */

ttfd = tt_fd();

tt_open returns the procid for your process and sets it as the default procid; tt_fd returns a file descriptor for your current procid that will become active when a message arrives for your application.

Caution - Your application must call tt_open before other tt_ calls are made; otherwise, errors may occur. However, there are a few exceptions: tt_default_session_set and tt_X_session can be called before tt_open to control to which sesion you connect. tt_feature_required and tt_feature_enabled may be called when using ToolTalk in a Multi-Threaded environment. The ToolTalk filename mapping API calls, tt_file_netfile, tt_netfile_file, tt_host_file_netfile, and tt_host_netfile_file may be called without ever calling tt_open.

When tt_open is the first call made to the ToolTalk service, it sets the initial session as the default session. The default session identifier (sessid) is important to the delivery of ToolTalk messages. The ToolTalk service automatically fills in the default sessid if an application does not explicitly set the session message attribute. If the message is scoped to TT_SESSION, the message will be delivered to all applications in the default session that have registered interest in this type of message.

Registering in a Specified Session

To register in a session other than the initial session, your program must find the name of the other session, set the new session as the default, and register with the ToolTalk service.

The following code sample shows how to join an X session named somehost:0 that is not your initial session.

char   *my_session;
char   *my_procid;

my_session = tt_X_session("somehost:0");
tt_default_session_set(my_session);
my_procid = tt_open();
ttfd = tt_fd();

Note - The required calls must be in the specified order.

1. tt_X_session();

   This call retrieves the name of the session associated with an X display server. tt_X_session() takes the argument char *xdisplay_name

   where xdisplay_name is the name of an X display server (in this example, somehost:0).

2. tt_default_session_set();

   This call sets the new session as the default session.

3. tt_open();

   This call returns the procid for your process and sets it as the default procid.

4. tt_fd();

   This call returns a file descriptor for your current procid.

Registering in Multiple Sessions

There may be cases when you want to send and receive your messages in different sessions. To register in multiple sessions, your program must find the identifiers of the sessions to which it wants to connect, set the new sessions, and register with the ToolTalk service.

The following code sample shows how to connect procid to sessid1, and procid2 to sessid2.

tt_default_session_set(sessid1);
my_procid1 = tt_open();
tt_default_session_set(sessid2);
my_procid2 = tt_open();
tt_fd2 = tt_fd();

You can then use tt_default_procid_set() to switch between the sessions.

Setting Up to Receive Messages

Before your application can receive messages from other applications, you must set up your process to watch for arriving messages. When a message arrives for your application, the file descriptor becomes active. The code you use to alert your application that the file descriptor is active depends on how your application is structured.

For example, a program that uses the XView notifier, through the xv_main_loop or notify_start calls, can have a callback function invoked when the file descriptor becomes active. The following code sample invokes notify_set_input_func with the handle for the message object as a parameter.

	/*
	 * Arrange for XView to call receive_tt_message when the
	 * ToolTalk file descriptor becomes active.
	 */
	notify_set_input_func(base_frame,
								(Notify_func)receive_tt_message,
							ttfd);

Table 7-2 describes various window toolkits and the call used to watch for arriving messages.

Table 7-2 Code Used to Watch for Arriving Messages