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tt_message_callback_add(3)


CDE


NAME

  tt_message_callback_add - register a callback function


SYNOPSIS

  #include <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_c.h(5). 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_callback_add; 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.


SEE ALSO

  tt_c.h(5), tt_message_receive(3)

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