tt_message_callback_add(3)

NAME

tt_message_callback_add − register a callback function

SYNOPSIS

#include <Tt/tt_c.h>
Tt_status tt_message_callback_add(Tt_message m,
Tt_message_callback f);

DESCRIPTION

The tt_message_callback_add() function registers a callback function to be automatically invoked by tt_message_receive(3) whenever a reply or other state-change to this message is returned.

The callback is defined in <Tt/tt_c.h>. If the callback returns TT_CALLBACK_CONTINUE, other callbacks will be run; if no callback returns TT_CALLBACK_PROCESSED, tt_message_receive() returns the message. If the callback returns TT_CALLBACK_PROCESSED, no further callbacks are invoked for this event; tt_message_receive() does not return the message.

The m argument is the opaque handle for the message involved in this operation. The f argument is the message callback to be run.

The pattern handle will be NULL if the message did not match a dynamic pattern. This is usually the case for message callbacks.

RETURN VALUE

Upon successful completion, the tt_message_callback_add() function returns the status of the operation as one of the following Tt_status values:

TT_OK
The operation completed successfully.

TT_ERR_NOMP
The ttsession(1) process is not running and the ToolTalk service cannot restart it.

TT_ERR_POINTER
The pointer passed does not point to an object of the correct type for this operation.

APPLICATION USAGE

These callbacks are invoked from tt_message_receive(); the program must, therefore, call tt_message_receive() when the file descriptor returned by tt_fd() becomes active.

The application can use tt_message_callback_add() to create wrappers for ToolTalk messages. For example, a library routine can construct a request, attach a callback to the message, send the message, and process the reply in the callback. When the callback returns TT_CALLBACK_PROCESSED, the message reply is not returned to the main program; the message and reply are, therefore, completely hidden.

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