-- 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.