Retrieving Messages

When a message arrives for your process, the ToolTalk-supplied file descriptor becomes active. When notified of the active state of the file descriptor, your process must call tt_message_receive to get a handle for the incoming message.

Example 11–1 illustrates how to receive a message.

Example 11–1 Receiving a Message

/*
 * When a ToolTalk message is available, receive it; if it's a
 * ttsample1_value message, update the gauge with the new value.
 */
void
receive_tt_message()
{
	Tt_message msg_in;
	int mark;
	int val_in;

	msg_in = tt_message_receive();

	/*
	 * It's possible that the file descriptor would become active
	 * even though ToolTalk doesn't really have a message for us.
	 * The returned message handle is NULL in this case.
	 */

	if (msg_in == NULL) return;

Handles for messages remain constant. For example, when a process sends a message, both the message and any replies to the message have the same handle as the sent message. Example 11–2 is an example of how you can check the message state for TT_HANDLED.

Example 11–2 Code Checking the Message State

Tt_message m, n;
m = tt_message_create();
...
tt_message_send(m);

... wait around for tt_fd to become active

n = tt_message_receive();
if (m == n) {
	/* This is the reply to the message we sent */
	if (TT_HANDLED == tt_message_state(m) ) {
			/* The receiver has handled the message so we can go
on */
			...
	}
} else {
	/* This is a new message coming in */
)

Identifying and Processing Messages Easily

To easily identify and process messages received by you:

• Add a callback to a dynamic pattern with tt_pattern_callback_add. When you retrieve the message, the ToolTalk service will invoke any message or pattern callbacks. See Chapter 9, Dynamic Message Patterns for more information on placing callbacks on patterns.

• Retrieve the message's opnum if you are receiving messages that match your ptype message patterns.

Recognizing and Handling Replies Easily

To easily recognize and handle replies to messages sent by you:

• Place specific callbacks on requests before you send them with tt_message_callback_add. See Chapter 8, Sending Messages for more information on placing callbacks on messages.

• Compare the handle of the message you sent with the message you just received. The handles will be the same if the message is a reply.

• Add information meaningful to your application on the request with the tt_message_user_set call.