-- FileInstance.mesa
-- Last edited by
--   Taft on October 25, 1982 11:01 am
--   Kolling on November 12, 1982 4:35 pm


DIRECTORY
   AlpineEnvironment
      USING[FileID, LockMode, PageCount, VolumeID],
   AlpineInternal
      USING[FileHandle, FileInstanceHandle, TransHandle];


FileInstance: CEDAR DEFINITIONS =

BEGIN


Handle: TYPE = AlpineInternal.FileInstanceHandle;


Register: PROCEDURE [trans: AlpineInternal.TransHandle, volumeID:
 AlpineEnvironment.VolumeID, fileID: AlpineEnvironment.FileID] RETURNS [handle: Handle];
-- errors defined in this interface: none.
-- Finds or creates a handle for the supplied trans, volume, and file, and increments use count on the returned handle.  If the handle is created, it is also entered in the FileInstance list for its transaction and FileMap.Register is called.

Unregister: PROCEDURE [handle: Handle];
-- errors defined in this interface: none.
-- Decrements use count on handle.  If the use count becomes zero and delta version is 0 (i.e., if the file has not been updated), deletes it from the FileInstance list for its transaction and calls FileMap.Unregister.  (Updated files are taken care of by FlushTransState.)

FlushTransState: PROCEDURE [trans: AlpineInternal.TransHandle];
-- errors defined in this interface: none.
-- When this is called, it is a fatal error if any handle in this transaction's FileInstance list has useCount # 0 or delta version = 0.  Otherwise, FileMap.Unregister is called for each handle.



-- Access to immutable attributes.

GetFileHandle: PROCEDURE [handle: Handle] RETURNS [fileHandle: AlpineInternal.FileHandle];
-- errors defined in this interface: none.

GetTransHandle: PROCEDURE [handle: Handle] RETURNS [trans: AlpineInternal.TransHandle];
-- errors defined in this interface:  none.

GetVolumeID: PROCEDURE [handle: Handle] RETURNS [volumeID:
 AlpineEnvironment.VolumeID];
-- errors defined in this interface: none.

GetFileID: PROCEDURE [handle: Handle] RETURNS [fileID: AlpineEnvironment.FileID];
-- errors defined in this interface: none.

GetVolumeIDAndFileID: PROCEDURE [handle: Handle] RETURNS [volumeID:
 AlpineEnvironment.VolumeID, fileID: AlpineEnvironment.FileID];
-- errors defined in this interface: none.



-- Access to read/write attributes.

GetDeltaVersion: PROCEDURE [handle: Handle] RETURNS [delta: LONG INTEGER];
-- errors defined in this interface: none.
-- Returns the most recent value set by SetMaxDeltaVersion, or zero if SetMaxDeltaVersion
-- hasn't been called.  A nonzero value means that the file has been updated by this transaction.

SetMaxDeltaVersion: PROCEDURE [handle: Handle, increment: LONG INTEGER _ 1];
-- errors defined in this interface: none.
-- Sets the delta version to the MAX of increment and its existing value.

GetHighWaterMark: PROCEDURE [handle: Handle] RETURNS [highWaterMark:
 AlpineEnvironment.PageCount];
-- errors defined in this interface:  none.
-- returns the uncommitted highWaterMark, for this transaction.  Initialize value is
-- LAST[PageCount].

SetHighWaterMark: PROCEDURE [handle: Handle, highWaterMark:
  AlpineEnvironment.PageCount] RETURNS [oldHighWaterMark: AlpineEnvironment.PageCount];
-- errors defined in this interface:  none.
 
GetLockMode: PROCEDURE [handle: Handle] RETURNS [lock: AlpineEnvironment.LockMode];
-- errors defined in this interface:  none.

SetLockMode: PROCEDURE [handle: Handle, lock: AlpineEnvironment.LockMode];
-- errors defined in this interface:  none.



-- Enumeration.

GetNextHandleForTrans: PROCEDURE [trans: AlpineInternal.TransHandle, handle: Handle _
 NIL] RETURNS [nextHandle: Handle];
-- errors defined in this interface: none.
-- handle = NIL starts a new enumeration, and nextHandle = NIL is returned when the
-- enumeration is exhausted.  The FileInstance list is assumed to not be being
-- modified during this enumeration.  When handle is non-NIL, not finding it is a fatal error.




END.