Organization of the Code

The organization of the code is shown in figure . This hierachy is present in every DD routine. It should be noted that the ``normal user'' calls only user routines ( ddu_xxx), whereas the system routines ( dds_xxx) are typically called either by a control program or the main user interface.

 
Figure:   Overview of the DD code.

The processes attached to the DD system can be divided into three classes:

• DD masters:
  These are processes that have called at a given time dds_create(). This routine creates the DD system (if it doesn't exist) or attaches to it (if it exists).
• DD consumers/producers:
  These are processes that are attached to a DD fifo (i.e. processes that called ddu_init).
• Monitor processes:
  These are processes that attached to the DD system, but do not insert or retrieve any events (i.e. they are not attached to a fifo). They typically only called ddu_attach() .