-- FilePageMgrIO.mesa
-- Last edited by
--   Kolling on January 27, 1984 2:39:57 pm PST

DIRECTORY

      File
         USING[Handle, PageCount, PageNumber, RC, Reason];


FilePageMgrIO: CEDAR DEFINITIONS =


BEGIN


-- The (controlling) process:  starts the "sequential" io by calling RegisterRequest (which Notifies IdlerNeeded), and then loops 
on GetNext until that returns error # ok OR workToDo = FALSE.  (GetNext does not return error # ok OR workToDo = FALSE to the 
controller until its idler, if any, has completed.)  If the controller detects an error while doing io, it must call LogError to 
terminate this sequence;  LogError will not return to the controller until the associated idler, if any, has stopped.  It is the 
controller's responsibility to report errors to its caller.

-- An idler sits around waiting for IdlerNeeded;  when it sees it, it calls RegisterIdler and if workToDo # FALSE it then loops on 
GetNext until workToDo = FALSE  (GetNext doesn't report errors to the idler, it just stops it with workToDo = FALSE).  If the idler 
detects an error while doing io, it must call LogError to terminate this sequence and inform the controller of the error.

-- By setting maxRequests in FilePageMgrIOImpl suitably, we can optimize for File really scheduling disk requests or (current case) 
only doing FCFS.



IORequest: TYPE = RECORD[filePageNumber: File.PageNumber, nPages: File.PageCount,
   vM: LONG POINTER];
IOType: TYPE = {read, write};
Who: TYPE = {idler, controller};


RegisterRequest: PROCEDURE[controllingProcess: PROCESS, io: IOType,
 file: File.Handle, list: LIST OF IORequest] RETURNS[iORequest: IORequest];
 -- non system fatal errors:  none.
   

GetNext: PROCEDURE[controllingProcess: PROCESS, who: Who] RETURNS[error: File.RC,
 errorIORequest: IORequest, workToDo: BOOLEAN, iORequest: IORequest];
 -- non system fatal errors:  none.
   

LogError: PROCEDURE[controllingProcess: PROCESS, who: Who, why: File.Reason,
 errorIORequest: IORequest];
 -- non system fatal errors:  none.
 

DoIO: PROCEDURE[io: IOType, file: File.Handle, iORequest: IORequest];  -- utility routine.
 -- non system fatal errors:  none.


END.

                                                                Edit Log

Initial: Kolling: August 25, 1983 6:30 pm: definitions module for FilePageManager io.