Additional Rules for an Asynchronous Processor

In addition to the rules for a Standard Processor, Asynchronous Processors must abide by the following rules that require them to call the Data Structure Manager (DSM). See section 4.3.6 for sample code that does this.

• A processor which does not modify the data structure in any way (note this includes I/O which merely moves the structure between memory and some external media) should process without making any call to the DSM.

• A processor, which does modify the data structure, must report that is about to process to the DSM, using the routine DSM_PRO_PREPARE. If, and only if, the call to the processor results in the data structure being modified the routine DSM_PRO_COMPLETE must be called after processing. This call must be made even if the result is considered a failure.

• A processor that produces outputs must be able to handle the situation that its outputs (if any) already exist. 3 responses are possible:-

  Insert

  Do nothing.

  Replace

  Replace outputs removing any downstream processing.

  Append

  Append additional outputs removing any downstream processing.

  A MODE parameter passed to the processor determines the required response. This parameter should be passed to DSM_PRO_PREPARE which will remove unwanted downstream processing and signal quit in the case of insert mode with existing outputs.

• The processor must support both Insert and Replace modes; Append is optional.

• The processor must provide a separate routine that is to be called if its action is to be undone. This is called its Delete Outputs routine. A processor that does not modify the data structure should return KSU_NOOP as the return code. In all other cases, the routine must delete all outputs and undo any temporary modification to its inputs.