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sources/rms/rmsbuf.b36
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%TITLE 'B U F F E R -- file buffer routines'
!<BLF/REQUIRE 'RMSBLF.REQ'>
MODULE buffer (IDENT = '2.0'
) =
BEGIN
!
! COPYRIGHT (C) DIGITAL EQUIPMENT CORPORATION 1984, 1986.
! ALL RIGHTS RESERVED.
!
! THIS SOFTWARE IS FURNISHED UNDER A LICENSE AND MAY BE USED AND
! COPIED ONLY IN ACCORDANCE WITH THE TERMS OF SUCH LICENSE AND WITH
! THE INCLUSION OF THE ABOVE COPYRIGHT NOTICE. THIS SOFTWARE OR
! ANY OTHER COPIES THEREOF MAY NOT BE PROVIDED OR OTHERWISE MADE
! AVAILABLE TO ANY OTHER PERSON. NO TITLE TO AND OWNERSHIP OF THE
! SOFTWARE IS HEREBY TRANSFERRED.
!
! THE INFORMATION IN THIS SOFTWARE IS SUBJECT TO CHANGE WITHOUT
! NOTICE AND SHOULD NOT BE CONSTRUED AS A COMMITMENT BY DIGITAL
! EQUIPMENT CORPORATION.
!
! DIGITAL ASSUMES NO RESPONSIBILITY FOR THE USE OR RELIABILITY OF
! ITS SOFTWARE ON EQUIPMENT THAT IS NOT SUPPLIED BY DIGITAL.
!
!++
! FACILITY: RMS
!
! ABSTRACT:
!
! BUFFER contains all routines which process
! file buffers within RMS-20.
!
! ENVIRONMENT: Deep within RMS, interrupts deferred until JSYS return.
!
! AUTHOR: Ron Lusk , CREATION DATE: 15-Mar-83
!
! MODIFIED BY:
!
! , : VERSION
! 01 -
!--
!
! TABLE OF CONTENTS
!
!
! GETBUF -- allocate a file buffer
! PUTBUF -- Deallocate a file buffer
!
!
! INCLUDE FILES:
!
REQUIRE 'rmsreq';
!
! MACROS:
!
!<BLF/MACRO>
MACRO
!
! SETLRU (buffer) sets the buffer's Least Recently
! Used count to the current buffer access count.
! This count is incremented each time a buffer is
! allocated and is never decremented, thus giving
! a "timestamp" of sorts for determining age of
! a given buffer.
!
setlru (a) =
a [0, wrd] = .bufacc %;
!
! EQUATED SYMBOLS:
!
GLOBAL BIND
bufrv = 2^24 + 0^18 + 400; ! Current edit level
!
! OWN STORAGE:
!
! None.
!
! EXTERNAL REFERENCES:
!
! None.
!
%SBTTL 'GETBUF -- allocate a file buffer'
GLOBAL ROUTINE getbuf (fpage, bsize, contigflag, p_bpage, p_incore, p_bfdadr) =
!++
! FUNCTIONAL DESCRIPTION:
!
! GETBUF allocates a buffer for a specified number of
! file pages beginning with the specified file page.
! There are four cases which may occur (listed here in
! decreasing priority):
!
! 1) Specified file page is still mapped into our
! process;
! 2) A buffer is available (use one with smallest LRU
! count, which is the least recently used, except
! that empty buffers will be used before the file
! pages in unused buffers are flushed);
! 3) A buffer must be allocated from free storage;
! 4) No buffer is available (give failure return).
!
!
! FORMAL PARAMETERS
!
! FPAGE - File page number
! BSIZE - Bucket/buffer size in pages
! CONTIGFLAG - Buffers should be allocated
! contiguously (see note below)
! BPAGE - Buffer page number (returned to
! caller)
! INCORE - if page is in core (if false, caller
! must map it) (returned to caller)
! BFDADR - adress of buffer descriptor (if 0,
! then called by Free Storage Manager
! (returned to caller)
!
! IMPLICIT INPUTS
!
! ?
!
! COMPLETION CODES:
!
! TRUE - Got buffer, (BPAGE, INCORE, and
! BFDADR will be set)
! FALSE - could not get buffer, no free
! storage
!
! SIDE EFFECTS:
!
! ?
!
! NOTES:
!
! 1) If the page was not found in any of the core
! buffers, then INCORE will be false and it is
! then the caller's responsibility to map the file
! page into the buffer returned by this routine.
!
! 2) If CONTIGFLAG is non-zero (not TRUE, just merely
! non-zero), then it means that if we don't find
! the page in our buffers, we should completely
! fill up our buffer pool by mapping all pages
! that will fit. Currently, this facility is used
! only for Sequential/Relative files which use
! Read-ahead.
!--
BEGIN
BIND
bpage = .p_bpage,
incore = .p_incore,
bfdadr = .p_bfdadr : REF BLOCK;
EXTERNAL
bfound, ! # buffers found in chain
bfault, ! # buffers not found in chain
bfcore; ! # buffers allocated
! from free core
LOCAL
usecount, ! # Of users of this buffer
bfdptr : REF BLOCK,
lruptr : REF BLOCK, ! Ptr to LRU word for BFDPTR
lrumin;
TRACE ('GETBUF');
!+
! Increment counter of calls to GETBUF
! (this is used to fill in the LRU count
! for a buffer).
!-
bufacc = .bufacc + 1; ! Incr count of buffer accesses
%IF dbug
%THEN
!
! Check our input
!
IF .contigflag AND idxfile THEN rmsbug (msgflags);
%FI
!+
! Search for a buffer to return to caller
!-
bfdadr = 0; ! Reset ptr to available buffer
lrumin = plusinfinity; ! Preset smallest LRU
INCR j FROM bfdoffset !
TO bfdoffset + .rst [rstbfdcount] - 1 !
BY 1 !
DO
BEGIN
bfdptr = .j; ! Setup ptr to this
! buffer descriptor
lruptr = .j + .rst [rstbfdcount]; ! Point at its LRU word
!+
! 1. Check if the specified file
! page is in this buffer.
!-
IF .bfdptr [bfdfpage] EQL .fpage !
AND .bfdptr [bfdbktsiz] NEQ 0 !
THEN
BEGIN ! Return file page
! already in core
setlru (lruptr); ! Set LRU count
bfdptr [bfdusecount] = .bfdptr [bfdusecount] + 1; ! Incr users
bpage = .bfdptr [bfdbpage]; ! Return buffer page no.
incore = true; ! Return "file page is in core"
bfdadr = .bfdptr; ! Pointer to buffer descriptor
bfound = .bfound + 1; ! Bump count of found buffs
RETURN true; ! Give good return to caller
END;
!+
! 2. Check if this buffer is empty or
! available with has smaller LRU count.
!-
IF .bfdptr [bfdbktsiz] EQL 0 OR !
(.bfdptr [bfdusecount] EQL 0 AND !
.lruptr [0, wrd] LSS .lrumin) !
THEN
BEGIN ! Save pointer to LRU buffer
bfdadr = .bfdptr; ! Tentatively set LRU buffer
IF .bfdptr [bfdbktsiz] EQL 0 THEN EXITLOOP; ! Use 1st empty buffer
lrumin = .lruptr [0, wrd] ! Reset lowest LRU seen
END
END; ! Search iteration
!+
! If contiguous allocation is needed,
! assume we found the first buffer.
!-
IF .contigflag NEQ false !
THEN
bfdadr = bfdoffset;
!+
! Check if we found a buffer to use (empty or LRU)
!-
IF (.bfdadr NEQ 0)
THEN
BEGIN ! Return this buffer to caller
usecount = 1; ! this buffer is busy
bfdptr = .bfdadr; ! Set up moving pointer
bpage = .bfdptr [bfdbpage]; ! Return buffer page
! number to caller
incore = false; ! Return "page must be
! mapped from file" to caller
bfault = .bfault + 1; ! Bump # of faults
!+
! Do this loop once for each buffer if
! contiguous allocation, only once otherwise.
!-
INCR j FROM 1 TO .rst [rstbfdcount] DO
BEGIN
lruptr = .bfdptr + .rst [rstbfdcount]; ! Point at chosen LRU
IF bfdupd (bfdptr) ! Do old contents
! need putting out?
THEN
pagout (.fst [fstjfn], ! JFN
.bfdptr [bfdfpage], ! File page number
.bfdptr [bfdbpage], ! Page number of buffer
.bfdptr [bfdbktsiz]); ! Number of pages to write
clearbfdupd (bfdptr); ! Reset flag
setlru (lruptr); ! Set LRU count for buffer
bfdptr [bfdusecount] = .usecount; ! Set initial use count
! for buffer
bfdptr [bfdfpage] = .fpage; ! Set file page number
! that is in buffer
bfdptr [bfdbktsiz] = .bsize; ! For demand flush
! in later GETBUF
%IF dbug
%THEN
begindebug (dbio);
printvalue (' PAGE FAULT FOR PAGE: ', fpage);
enddebug;
%FI
!+
! We can exit in the normal case.
!-
IF .contigflag EQL false THEN RETURN true;
bfdptr = .bfdptr + 1; ! Bump pointer
lruptr = .lruptr + 1; ! Bump pointer
fpage = .fpage + .bsize; ! And page number
usecount = 0 ! Other buffers are free
END;
!+
! We have set up all buffer descriptors
! for contiguous allocation.
!-
RETURN true
END;
!+
! Didn't find buffer. ask free storage manager for buffer.
!-
IF (bpage = gpage (.bsize ! Page count
)) NEQ false
THEN
BEGIN ! Got buffer from FSM
incore = false; ! Return "Page Must
! Be Mapped" to caller
bfcore = .bfcore + 1; ! Bump count of free core buffs
RETURN true ! Successful return
END
ELSE
returnstatus (er$dme) ! Return "Can't get buffer"
END; ! End of GETBUF
%SBTTL 'PUTBUF -- Deallocate a file buffer'
GLOBAL ROUTINE putbuf (bsize, bpage, incore, bfdadr : REF BLOCK) =
!++
! FUNCTIONAL DESCRIPTION:
!
! PUTBUF deallocates a buffer. If the buffer was
! allocated from free storage, then the Free Storage
! Manager is called to release the pages composing the
! buffer. Otherwise, the buffer is "returned" to the
! buffer pool (note that if there is more than one
! user of the buffer then the buffer becomes free only
! after the last user calls this routine.
!
! FORMAL PARAMETERS
!
! BSIZE - bucket/buffer size in pages
! BPAGE - buffer page number
! INCORE - if page is in core (if FALSE, it was
! pmapped to file; FALSE also means
! that the buffer is now empty)
! BFDADR - address of buffer descriptor
!
! IMPLICIT INPUTS
!
! NONE.
!
! COMPLETION CODES:
!
! TRUE - always.
!
! SIDE EFFECTS:
!
! ?
!
! NOTES:
! 1) If the address of the buffer descriptor (BFDADR)
! in the bucket descriptor is null, this indicates
! that the buffer was not allocated from the
! buffer pool in the Record Status Table.
! Instead, it was allocated from the Free Storage
! Manager because all other buffers were already
! in use (this situation should not happen
! currently since a minimum of 3 buffers is
! allocated when a record stream is initiated).
!--
BEGIN
TRACE ('PUTBUF');
!+
! If buffer came from free storage, return it to the FSM.
!-
IF (.bfdadr EQL 0)
THEN ! Return buffer to FSM
BEGIN
ppage (.bpage, ! Page number
.bsize, ! Count
true); ! Kill Flag
RETURN true
END;
!+
! Decrement use count for buffer.
!-
BEGIN
REGISTER
tempac;
tempac = .bfdadr [bfdusecount];
IF .tempac EQL 0 THEN rmsbug (msgbna);
bfdadr [bfdusecount] = .tempac - 1; ! Decrement use count
END;
!+
! If buffer is now empty, and if there are
! no more users of the buffer, then make the
! Buffer Descriptor indicate that condition.
!-
IF (.incore EQL false) !
AND (.bfdadr [bfdusecount] EQL 0) !
THEN
bfdadr [bfdbktsiz] = 0; ! Indicate no data in buffer
RETURN true; ! Give "good" return to caller
END; ! End of PUTBUF
END ! End of Module BUFFER
ELUDOM