Action Data Type

MDSplus provides an action data type used for describing actions to be dispatched to action servers during a normal experiment cycle. An action consists of 5 parts but the current implementations of action dispatching only refernce the first three parts, a dispatch part, a task part and an errorlogs part (OpenVMS only). The dispatch part (See: DTYPE_DISPATCH) includes information such as which server should perform the task, when during the course of the shot cycle it should be executed, what MDSplus event should be issued when the task completes. The task part describes what is to be done when the action is executed. There are a couple different types of task types currently support (See: DTYPE_METHOD and DTYPE_ROUTINE). The errorlogs part is implemented only on OpenVMS. If this part contains a string consisting of a comma delimited list of user accounts, each user on the list will receive a OpenVMS cluster-wide broadcast message if this action fails during execution. The remaining parts were originally defined to hold statistics from the execution of the action but since this would require rewriting the action data (which is usually considered setup information and not writable in the pulse files) this feature was never used. This unused parts are called completion_message and performance.

The following shows some examples of creating and accessing an MDSplus action. These examples are written in TDI (the MDSplus expression evaluator language).

_MYACTION = BUILD_ACTION(
             BUILD_DISPATCH(2,"CAMAC_SERVER","STORE",50,"A12_42_DONE"),
             BUILD_METHOD(*,"STORE",A12_42)
            )
_DISPATCH = DISPATCH_OF(_MYACTION)
_TASK = TASK_OF(_MYACTION)

The above example builds an action item consisting of a dispatch item and a metho item. The dispatch item is specifying that this action should be run on the action server called "CAMAC_SERVER" during the "STORE" phase using sequential scheduling, executed after all actions with sequence numbers between 1-49 have completed. When this action completes the dispatcher should issue the MDSplus event called "A12_42_DONE"). The task portion of the action is a method item specifying the "STORE" action is to be performed on the A14_42 (tree node) device.

Normally actions are defined using tools such as the "traverser" and "actions" applications and the contents of actions are referenced by action dispatchers so you rarely need to build or access the parts of actions, dispatch and method items by hand.

The following table lists some of the functions available for creating and accessing actions: