-- FileIOPrivate.mesa
-- Last edited by
--   MBrown on September 17, 1983 8:42 pm
--   Teitelman on May 26, 1982 4:52 pm
-- Last Edited by: Levin, September 22, 1983 2:48 pm

	DIRECTORY
		FS USING [Lock, OpenFile, StreamOptions],
		Rope USING [ROPE],
		VM USING [Interval];
		
FileIOPrivate:  CEDAR DEFINITIONS =
	BEGIN
	ROPE: TYPE = Rope.ROPE;
	
	-- We model the behavior of a File IOStream with variables "file", "fileLen", and
	--"streamIndex", where
	--   file is an ARRAY [0..fileLen) OF CHAR
	--   streamIndex is an INT [0..fileLen]
	
	-- The real stream contains a lot of redundant state to make the frequently-used
	--operations GetChar and PutChar fast.  We shall list some invariant properties of
	--this state below.  These invariants hold on entry to and exit from each stream
	--operation. (Redundant properties, included for their intuitive value, are given in
	--parentheses.)
	
	-- We also define a piece of fictional state: trueDataBytesInBuffer. 
	-- trueDataBytesInBuffer ::= MIN[bufferBytes, fileLen - firstByteInBuffer].
	-- trueDataBytesInBuffer is too expensive for PutByte to maintain at all times, but it
	--is useful for other operations.
	
	DataHandle: TYPE = REF Data;
	FSDataHandle: TYPE = REF Data.fs;
	AlpineDataHandle: TYPE = REF Data.alpine;
	
	FileSystem: TYPE = {fs, alpine};
	
	Data: TYPE = RECORD [
		-- common part, followed by variant depending on FileSystem.
		-- order these components to optimize the code generated for GetChar and PutChar.
		index: CARDINAL _ 0,
			-- index is IN [0..bufferBytes].
			-- didPut AND index >= dataBytesInBuffer => trueDataBytesInBuffer = index.
		dataBytesInBuffer: CARDINAL _ 0,
			-- dataBytesInBuffer is IN [0..trueDataBytesInBuffer] => IN [0..bufferBytes].
			-- NOT didPut OR (didPut AND index <= dataBytesInBuffer) =>
			--   trueDataBytesInBuffer = dataBytesInBuffer.
		bufferBytes: CARDINAL _ 0,
			-- (see buffer below).
		eofInBuffer: BOOL _ FALSE,
			-- eofInBuffer <=> fileLen <= firstFileByteInBuffer + bufferBytes.
			-- (this means fileLen = 0, or file[fileLen-1] is contained in the buffer.  This
			--is a useful piece of redundant state; fortunately, none of the cheap operations
			--need to update it).
		didPut: BOOL _ FALSE,
			-- (somebody has done a Put and not updated dataBytesInBuffer, FileLength, and
			--bufferDirty).
		bufferDirty: BOOL _ FALSE,
			-- didPut OR bufferDirty => there exists some i IN [0..trueDataBytesInBuffer) such
			--that buffer[i] # file[i] as last read from file system.  (Not maintained for
			--Pilot because of its mapped files.)
		accessRights: FS.Lock,
		streamOptions: FS.StreamOptions,
		tiogaReader: BOOL _ FALSE,
			-- TRUE iff file is being read as a Tioga file (reading the plain text only).
			--This implies that the file length shown in the stream is not the true file length,
			--but instead is the Tioga plain text length.
		streamIsClosed: BOOL _ FALSE,
			-- stream.Close[] was called.
			-- (all operations should now raise StreamError[streamClosed]).
		firstFileByteInBuffer: INT _ 0,
			-- streamIndex = firstFileByteInBuffer + index.
			-- firstFileByteInBuffer < fileLen OR firstFileByteInBuffer = fileLen = 0.
			-- firstFileByteInBuffer MOD bytesPerPage = 0.
			-- (buffer[0] is indentified with file[firstFileByteInBuffer].  There is always
			--one file byte in the buffer unless file is empty.)
		fileLength: INT _ 0,
			-- NOT didPut => fileLen = fileLength.
			-- didPut AND index > dataBytesInBuffer => fileLen = firstFileByteInBuffer +
			--index.
		buffer: LONG POINTER TO PACKED ARRAY [0..0) OF CHAR _ NIL,
			-- (the current stream buffer.)
			-- buffer is really PACKED ARRAY [0..bufferBytes) OF CHAR.
			-- file[firstFileByteInBuffer..firstFileByteInBuffer+trueDataBytesInBuffer) = 
			--   buffer[0..trueDataBytesInBuffer)
			-- (in case of Pilot, buffer[0..bufferBytes) are always backed by pages of file.)
		bufferInterval: VM.Interval _ TRASH,
			-- (a space of length maxBufferPages pages for the stream buffer above. If buffer
			--= NIL, the space has not yet been created.)
		fileName: ROPE,
		body: SELECT type: FileSystem FROM
			fs => [
				fileHandle: FS.OpenFile,
				byteLength: INT, --current value of fileHandle.OpenInfo[].bytes
				byteSize: INT --current value of fileHandle.OpenInfo[].pages*bytesPerPage
				],
			alpine => [
				fileHandle: REF ANY, --AlpFile.Handle (includes transaction)
				byteLength: INT, --current value of fileHandle.ReadProperties[[byteLength: TRUE]]
				byteSize: INT --current value of fileHandle.GetSize[]*bytesPerPage
				],
			ENDCASE];

END.


CHANGE LOG

Created by MBrown on December 12, 1980  12:04 PM

Changed by MBrown on January 6, 1981  8:53 PM
-- Added Invalidate, added trans field to pilot data.

Changed by MBrown on January 16, 1981  10:00 AM
-- DataObject is now defined without using a Stream.Handle (copied structure from
--FileStreamImpl).

Changed by MBrown on January 18, 1981  1:00 AM
-- LeaderPage now defined here (but it uses something called FileStream.Subtype for its
--"dataType" field).

Changed by MBrown on 18-Jan-81 16:49:31
-- Added bufferDirty (for juniper stream use). and streamIsClosed (for diagnosis from
--the debugger).  Improved the description of invariants. 

Changed by MBrown on January 21, 1981  3:45 PM
-- Complete re-think of Pilot FileStream state, to make Put faster and generally reduce
--the number of expensive conversions betweeen pages and bytes.  Not yet implemented.

Changed by MBrown on January 22, 1981  3:12 PM
-- Improved comments on invariants.

Changed by MBrown on January 25, 1981  8:19 PM
-- Added Juniper variant of Data.

Changed by MBrown on 27-Jan-81 15:10:07
-- FileByteStreamJuniper -> Juniper.

Changed by MBrown on 29-Jan-81 20:43:05
-- Added JOpen, POpen.

Changed by Russ Atkinson on 26-May-81 14:07:10
-- CedarString -> Rope, LONG CARDINAL -> LONG INTEGER

Changed by MBrown on  7-Dec-81 10:30:56
-- Conversion to IO, INT, ROPE, etc.

Changed by MBrown on March 26, 1982 4:40 pm
-- Added tiogaReader field (this is redundant, but may be useful for debugging), and the
--IsThisThingATiogaFile proc.

Changed by Teitelman on May 26, 1982 4:52 pm
-- changed to safe language, name change IOStream -> IO.

Changed by MBrown on August 23, 1982 2:18 pm
-- Eliminated TEXTDataOffset, added bufferParms, renamed JOpen -> JuniperOpen,
--POpen -> ComSoftOpen, added CIFSOpen, added CIFS open file to pilot variant of Data.

Changed by MBrown on May 16, 1983 2:03 pm
-- Eliminated Juniper stuff, added Alpine stuff.

Changed by MBrown on June 22, 1983 11:29 am
-- Eliminated Pilot stuff, added FS stuff.

Changed by MBrown on September 17, 1983 8:42 pm
-- Eliminated all procs, since file stream impl is one module (FS).