-- BBAction.mesa
-- Russ Atkinson, November 1, 1982 3:30 pm

DIRECTORY
  AMEvents USING [Event];

BBAction: CEDAR DEFINITIONS = BEGIN

  ActionId: TYPE = INT;
    -- unique id for the action, these are never reused
    -- only positive integers are used

  Action: TYPE = REF ActionRep;
  
  Event: TYPE = AMEvents.Event;
  
  ActionKind: TYPE = {break, signal, other};
  
  ActionStatus: TYPE = {new, busy, pendingIn, pendingOut, dead};
  
  ActionRep: TYPE = RECORD
    [id: ActionId,
     rest: Action,
     kind: ActionKind,
     status: ActionStatus,
     event: Event,
     in,out: REF
     ];

  ActionError: ERROR;
    -- error given when pre-condition not met    

  NewAction: PROC [event: Event, kind: ActionKind _ other] RETURNS [Action];
    -- creates a new action with new id and given kind

  WaitForDataGiven: PROC [action: Action] RETURNS [REF];
    -- suspends caller (as pendingIn) until data is given
    -- data is returned from the call when proceding

  WaitForDataTaken: PROC [action: Action, out: REF];
    -- suspends caller (as pendingOut) until data (out) is taken
    -- when the data is taken, the process proceeds (busy)

  WaitForChange: PROC [changeCount: INT _ 0] RETURNS [INT];
    -- suspends caller until the change count is different than
    -- the given changeCount, then returns the new change count
    -- the changeCount will change for every time a process becomes pending,
    -- busy, or dead;  the change count may wrap around, but will always
    -- be > 0; therefore the default will not wait, but will return the
    -- current count

  ForceChange: PROC;
    -- forces a change to the change count

  GetChangeCount: PROC RETURNS [INT];
    -- get the current change count
  
  NextPendingAction: PROC [action: Action _ NIL] RETURNS [Action];
    -- returns the next eldest pending action
    -- returns NIL if no pending actions in list
    -- start with NIL to get most recent

  NextAction: PROC [action: Action _ NIL] RETURNS [Action];
    -- returns the next eldest action
    -- returns NIL if no actions in list
    -- start with NIL to get most recent

  GiveData: PROC [action: Action, in: REF];
    -- supplies the input data, allows the action to proceed

  TakeData: PROC [action: Action] RETURNS [REF];
    -- obtains the output data, allows the action to proceed  

  PeekData: PROC [action: Action] RETURNS [REF];
    -- obtains the output data, does not allow process to proceed  

  Abort: PROC [action: Action];
    -- aborts the pending action
    -- causes ERROR ABORTED in the associated process

  END.