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postgres/src/backend/storage/buffer/bufmgr.c
Vadim B. Mikheev eb08b3ce4f No more LateWrite, but there is WriteMode; 
SetBufferWriteMode () added;
FlushBuffer () fixed: now directly calls smgrflush () and
	releases buffer only if required by caller.
1997-01-16 08:11:41 +00:00

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/*-------------------------------------------------------------------------
*
* bufmgr.c--
* buffer manager interface routines
*
* Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/storage/buffer/bufmgr.c,v 1.8 1997/01/16 08:11:41 vadim Exp $
*
*-------------------------------------------------------------------------
*/
/*
*
* BufferAlloc() -- lookup a buffer in the buffer table. If
* it isn't there add it, but do not read it into memory.
* This is used when we are about to reinitialize the
* buffer so don't care what the current disk contents are.
* BufferAlloc() pins the new buffer in memory.
*
* ReadBuffer() -- same as BufferAlloc() but reads the data
* on a buffer cache miss.
*
* ReleaseBuffer() -- unpin the buffer
*
* WriteNoReleaseBuffer() -- mark the buffer contents as "dirty"
* but don't unpin. The disk IO is delayed until buffer
* replacement if WriteMode is BUFFER_LATE_WRITE.
*
* WriteBuffer() -- WriteNoReleaseBuffer() + ReleaseBuffer()
*
* DirtyBufferCopy() -- For a given dbid/relid/blockno, if the buffer is
* in the cache and is dirty, mark it clean and copy
* it to the requested location. This is a logical
* write, and has been installed to support the cache
* management code for write-once storage managers.
*
* FlushBuffer() -- as above but never delayed write.
*
* BufferSync() -- flush all dirty buffers in the buffer pool.
*
* InitBufferPool() -- Init the buffer module.
*
* See other files:
* freelist.c -- chooses victim for buffer replacement
* buf_table.c -- manages the buffer lookup table
*/
#include <sys/file.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <signal.h>
#include "postgres.h"
/* declarations split between these three files */
#include "storage/buf.h"
#include "storage/buf_internals.h"
#include "storage/bufmgr.h"
#include "storage/fd.h"
#include "storage/ipc.h"
#include "storage/shmem.h"
#include "storage/spin.h"
#include "storage/smgr.h"
#include "storage/lmgr.h"
#include "miscadmin.h"
#include "utils/builtins.h"
#include "utils/hsearch.h"
#include "utils/palloc.h"
#include "utils/memutils.h"
#include "utils/relcache.h"
#include "executor/execdebug.h" /* for NDirectFileRead */
#include "catalog/catalog.h"
extern SPINLOCK BufMgrLock;
extern int ReadBufferCount;
extern int BufferHitCount;
extern int BufferFlushCount;
static int WriteMode = BUFFER_LATE_WRITE; /* Delayed write is default */
static void WaitIO(BufferDesc *buf, SPINLOCK spinlock);
#ifndef HAS_TEST_AND_SET
static void SignalIO(BufferDesc *buf);
extern long *NWaitIOBackendP; /* defined in buf_init.c */
#endif /* HAS_TEST_AND_SET */
static Buffer ReadBufferWithBufferLock(Relation relation, BlockNumber blockNum,
bool bufferLockHeld);
static BufferDesc *BufferAlloc(Relation reln, BlockNumber blockNum,
bool *foundPtr, bool bufferLockHeld);
static int FlushBuffer (Buffer buffer, bool release);
static void BufferSync(void);
static int BufferReplace(BufferDesc *bufHdr, bool bufferLockHeld);
/* ---------------------------------------------------
* RelationGetBufferWithBuffer
* see if the given buffer is what we want
* if yes, we don't need to bother the buffer manager
* ---------------------------------------------------
*/
Buffer
RelationGetBufferWithBuffer(Relation relation,
BlockNumber blockNumber,
Buffer buffer)
{
BufferDesc *bufHdr;
LRelId lrelId;
if (BufferIsValid(buffer)) {
if (!BufferIsLocal(buffer)) {
bufHdr = &BufferDescriptors[buffer-1];
lrelId = RelationGetLRelId(relation);
SpinAcquire(BufMgrLock);
if (bufHdr->tag.blockNum == blockNumber &&
bufHdr->tag.relId.relId == lrelId.relId &&
bufHdr->tag.relId.dbId == lrelId.dbId) {
SpinRelease(BufMgrLock);
return(buffer);
}
return(ReadBufferWithBufferLock(relation, blockNumber, true));
} else {
bufHdr = &LocalBufferDescriptors[-buffer-1];
if (bufHdr->tag.relId.relId == relation->rd_id &&
bufHdr->tag.blockNum == blockNumber) {
return(buffer);
}
}
}
return(ReadBuffer(relation, blockNumber));
}
/*
* ReadBuffer -- returns a buffer containing the requested
* block of the requested relation. If the blknum
* requested is P_NEW, extend the relation file and
* allocate a new block.
*
* Returns: the buffer number for the buffer containing
* the block read or NULL on an error.
*
* Assume when this function is called, that reln has been
* opened already.
*/
extern int ShowPinTrace;
#undef ReadBuffer /* conflicts with macro when BUFMGR_DEBUG defined */
/*
* ReadBuffer --
*
*/
Buffer
ReadBuffer(Relation reln, BlockNumber blockNum)
{
return ReadBufferWithBufferLock(reln, blockNum, false);
}
/*
* is_userbuffer
*
* XXX caller must have already acquired BufMgrLock
*/
static bool
is_userbuffer(Buffer buffer)
{
BufferDesc *buf = &BufferDescriptors[buffer-1];
if (IsSystemRelationName(buf->sb_relname))
return false;
return true;
}
Buffer
ReadBuffer_Debug(char *file,
int line,
Relation reln,
BlockNumber blockNum)
{
Buffer buffer;
buffer = ReadBufferWithBufferLock(reln, blockNum, false);
if (ShowPinTrace && !BufferIsLocal(buffer) && is_userbuffer(buffer)) {
BufferDesc *buf = &BufferDescriptors[buffer-1];
fprintf(stderr, "PIN(RD) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
buffer, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[buffer - 1], file, line);
}
return buffer;
}
/*
* ReadBufferWithBufferLock -- does the work of
* ReadBuffer() but with the possibility that
* the buffer lock has already been held. this
* is yet another effort to reduce the number of
* semops in the system.
*/
static Buffer
ReadBufferWithBufferLock(Relation reln,
BlockNumber blockNum,
bool bufferLockHeld)
{
BufferDesc *bufHdr;
int extend; /* extending the file by one block */
int status;
bool found;
bool isLocalBuf;
extend = (blockNum == P_NEW);
isLocalBuf = reln->rd_islocal;
if (isLocalBuf) {
bufHdr = LocalBufferAlloc(reln, blockNum, &found);
} else {
ReadBufferCount++;
/* lookup the buffer. IO_IN_PROGRESS is set if the requested
* block is not currently in memory.
*/
bufHdr = BufferAlloc(reln, blockNum, &found, bufferLockHeld);
if (found) BufferHitCount++;
}
if (!bufHdr) {
return(InvalidBuffer);
}
/* if its already in the buffer pool, we're done */
if (found) {
/*
* This happens when a bogus buffer was returned previously and is
* floating around in the buffer pool. A routine calling this would
* want this extended.
*/
if (extend) {
/* new buffers are zero-filled */
memset((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
(void) smgrextend(bufHdr->bufsmgr, reln,
(char *) MAKE_PTR(bufHdr->data));
}
return (BufferDescriptorGetBuffer(bufHdr));
}
/*
* if we have gotten to this point, the reln pointer must be ok
* and the relation file must be open.
*/
if (extend) {
/* new buffers are zero-filled */
(void) memset((char *) MAKE_PTR(bufHdr->data), 0, BLCKSZ);
status = smgrextend(bufHdr->bufsmgr, reln,
(char *) MAKE_PTR(bufHdr->data));
} else {
status = smgrread(bufHdr->bufsmgr, reln, blockNum,
(char *) MAKE_PTR(bufHdr->data));
}
if (isLocalBuf)
return (BufferDescriptorGetBuffer(bufHdr));
/* lock buffer manager again to update IO IN PROGRESS */
SpinAcquire(BufMgrLock);
if (status == SM_FAIL) {
/* IO Failed. cleanup the data structures and go home */
if (! BufTableDelete(bufHdr)) {
SpinRelease(BufMgrLock);
elog(FATAL,"BufRead: buffer table broken after IO error\n");
}
/* remember that BufferAlloc() pinned the buffer */
UnpinBuffer(bufHdr);
/*
* Have to reset the flag so that anyone waiting for
* the buffer can tell that the contents are invalid.
*/
bufHdr->flags |= BM_IO_ERROR;
bufHdr->flags &= ~BM_IO_IN_PROGRESS;
} else {
/* IO Succeeded. clear the flags, finish buffer update */
bufHdr->flags &= ~(BM_IO_ERROR | BM_IO_IN_PROGRESS);
}
/* If anyone was waiting for IO to complete, wake them up now */
#ifdef HAS_TEST_AND_SET
S_UNLOCK(&(bufHdr->io_in_progress_lock));
#else
if (bufHdr->refcount > 1)
SignalIO(bufHdr);
#endif
SpinRelease(BufMgrLock);
if (status == SM_FAIL)
return(InvalidBuffer);
return(BufferDescriptorGetBuffer(bufHdr));
}
/*
* BufferAlloc -- Get a buffer from the buffer pool but dont
* read it.
*
* Returns: descriptor for buffer
*
* When this routine returns, the BufMgrLock is guaranteed NOT be held.
*/
static BufferDesc *
BufferAlloc(Relation reln,
BlockNumber blockNum,
bool *foundPtr,
bool bufferLockHeld)
{
BufferDesc *buf, *buf2;
BufferTag newTag; /* identity of requested block */
bool inProgress; /* buffer undergoing IO */
bool newblock = FALSE;
/* create a new tag so we can lookup the buffer */
/* assume that the relation is already open */
if (blockNum == P_NEW) {
newblock = TRUE;
blockNum = smgrnblocks(reln->rd_rel->relsmgr, reln);
}
INIT_BUFFERTAG(&newTag,reln,blockNum);
if (!bufferLockHeld)
SpinAcquire(BufMgrLock);
/* see if the block is in the buffer pool already */
buf = BufTableLookup(&newTag);
if (buf != NULL) {
/* Found it. Now, (a) pin the buffer so no
* one steals it from the buffer pool,
* (b) check IO_IN_PROGRESS, someone may be
* faulting the buffer into the buffer pool.
*/
PinBuffer(buf);
inProgress = (buf->flags & BM_IO_IN_PROGRESS);
*foundPtr = TRUE;
if (inProgress) {
WaitIO(buf, BufMgrLock);
if (buf->flags & BM_IO_ERROR) {
/* wierd race condition:
*
* We were waiting for someone else to read the buffer.
* While we were waiting, the reader boof'd in some
* way, so the contents of the buffer are still
* invalid. By saying that we didn't find it, we can
* make the caller reinitialize the buffer. If two
* processes are waiting for this block, both will
* read the block. The second one to finish may overwrite
* any updates made by the first. (Assume higher level
* synchronization prevents this from happening).
*
* This is never going to happen, don't worry about it.
*/
*foundPtr = FALSE;
}
}
#ifdef BMTRACE
_bm_trace((reln->rd_rel->relisshared ? 0 : MyDatabaseId), reln->rd_id, blockNum, BufferDescriptorGetBuffer(buf), BMT_ALLOCFND);
#endif /* BMTRACE */
SpinRelease(BufMgrLock);
return(buf);
}
*foundPtr = FALSE;
/*
* Didn't find it in the buffer pool. We'll have
* to initialize a new buffer. First, grab one from
* the free list. If it's dirty, flush it to disk.
* Remember to unlock BufMgr spinlock while doing the IOs.
*/
inProgress = FALSE;
for (buf = (BufferDesc *) NULL; buf == (BufferDesc *) NULL; ) {
/* GetFreeBuffer will abort if it can't find a free buffer */
buf = GetFreeBuffer();
/*
* But it can return buf == NULL if we are in aborting
* transaction now and so elog(WARN,...) in GetFreeBuffer
* will not abort again.
*/
if ( buf == NULL )
return (NULL);
/*
* There should be exactly one pin on the buffer after
* it is allocated -- ours. If it had a pin it wouldn't
* have been on the free list. No one else could have
* pinned it between GetFreeBuffer and here because we
* have the BufMgrLock.
*/
Assert(buf->refcount == 0);
buf->refcount = 1;
PrivateRefCount[BufferDescriptorGetBuffer(buf) - 1] = 1;
if (buf->flags & BM_DIRTY) {
bool smok;
/*
* Set BM_IO_IN_PROGRESS to keep anyone from doing anything
* with the contents of the buffer while we write it out.
* We don't really care if they try to read it, but if they
* can complete a BufferAlloc on it they can then scribble
* into it, and we'd really like to avoid that while we are
* flushing the buffer. Setting this flag should block them
* in WaitIO until we're done.
*/
inProgress = TRUE;
buf->flags |= BM_IO_IN_PROGRESS;
#ifdef HAS_TEST_AND_SET
/*
* All code paths that acquire this lock pin the buffer
* first; since no one had it pinned (it just came off the
* free list), no one else can have this lock.
*/
Assert(S_LOCK_FREE(&(buf->io_in_progress_lock)));
S_LOCK(&(buf->io_in_progress_lock));
#endif /* HAS_TEST_AND_SET */
/*
* Write the buffer out, being careful to release BufMgrLock
* before starting the I/O.
*
* This #ifndef is here because a few extra semops REALLY kill
* you on machines that don't have spinlocks. If you don't
* operate with much concurrency, well...
*/
smok = BufferReplace(buf, true);
#ifndef OPTIMIZE_SINGLE
SpinAcquire(BufMgrLock);
#endif /* OPTIMIZE_SINGLE */
if ( smok == FALSE )
{
elog(NOTICE, "BufferAlloc: cannot write block %u for %s/%s",
buf->tag.blockNum, buf->sb_dbname, buf->sb_relname);
inProgress = FALSE;
buf->flags |= BM_IO_ERROR;
buf->flags &= ~BM_IO_IN_PROGRESS;
#ifdef HAS_TEST_AND_SET
S_UNLOCK(&(buf->io_in_progress_lock));
#else /* !HAS_TEST_AND_SET */
if (buf->refcount > 1)
SignalIO(buf);
#endif /* !HAS_TEST_AND_SET */
PrivateRefCount[BufferDescriptorGetBuffer(buf) - 1] = 0;
buf->refcount--;
if ( buf->refcount == 0 )
{
AddBufferToFreelist(buf);
buf->flags |= BM_FREE;
}
buf = (BufferDesc *) NULL;
}
else
{
BufferFlushCount++;
buf->flags &= ~BM_DIRTY;
}
/*
* Somebody could have pinned the buffer while we were
* doing the I/O and had given up the BufMgrLock (though
* they would be waiting for us to clear the BM_IO_IN_PROGRESS
* flag). That's why this is a loop -- if so, we need to clear
* the I/O flags, remove our pin and start all over again.
*
* People may be making buffers free at any time, so there's
* no reason to think that we have an immediate disaster on
* our hands.
*/
if (buf && buf->refcount > 1) {
inProgress = FALSE;
buf->flags &= ~BM_IO_IN_PROGRESS;
#ifdef HAS_TEST_AND_SET
S_UNLOCK(&(buf->io_in_progress_lock));
#else /* !HAS_TEST_AND_SET */
if (buf->refcount > 1)
SignalIO(buf);
#endif /* !HAS_TEST_AND_SET */
PrivateRefCount[BufferDescriptorGetBuffer(buf) - 1] = 0;
buf->refcount--;
buf = (BufferDesc *) NULL;
}
/*
* Somebody could have allocated another buffer for the
* same block we are about to read in. (While we flush out
* the dirty buffer, we don't hold the lock and someone could
* have allocated another buffer for the same block. The problem
* is we haven't gotten around to insert the new tag into
* the buffer table. So we need to check here. -ay 3/95
*/
buf2 = BufTableLookup(&newTag);
if (buf2 != NULL) {
/* Found it. Someone has already done what we're about
* to do. We'll just handle this as if it were found in
* the buffer pool in the first place.
*/
if ( buf != NULL )
{
#ifdef HAS_TEST_AND_SET
S_UNLOCK(&(buf->io_in_progress_lock));
#else /* !HAS_TEST_AND_SET */
if (buf->refcount > 1)
SignalIO(buf);
#endif /* !HAS_TEST_AND_SET */
/* give up the buffer since we don't need it any more */
buf->refcount--;
PrivateRefCount[BufferDescriptorGetBuffer(buf) - 1] = 0;
AddBufferToFreelist(buf);
buf->flags |= BM_FREE;
buf->flags &= ~BM_IO_IN_PROGRESS;
}
PinBuffer(buf2);
inProgress = (buf2->flags & BM_IO_IN_PROGRESS);
*foundPtr = TRUE;
if (inProgress) {
WaitIO(buf2, BufMgrLock);
if (buf2->flags & BM_IO_ERROR) {
*foundPtr = FALSE;
}
}
SpinRelease(BufMgrLock);
return(buf2);
}
}
}
/*
* At this point we should have the sole pin on a non-dirty
* buffer and we may or may not already have the BM_IO_IN_PROGRESS
* flag set.
*/
/*
* Change the name of the buffer in the lookup table:
*
* Need to update the lookup table before the read starts.
* If someone comes along looking for the buffer while
* we are reading it in, we don't want them to allocate
* a new buffer. For the same reason, we didn't want
* to erase the buf table entry for the buffer we were
* writing back until now, either.
*/
if (! BufTableDelete(buf)) {
SpinRelease(BufMgrLock);
elog(FATAL,"buffer wasn't in the buffer table\n");
}
/* record the database name and relation name for this buffer */
strcpy (buf->sb_relname, reln->rd_rel->relname.data);
strcpy (buf->sb_dbname, GetDatabaseName());
/* remember which storage manager is responsible for it */
buf->bufsmgr = reln->rd_rel->relsmgr;
INIT_BUFFERTAG(&(buf->tag),reln,blockNum);
if (! BufTableInsert(buf)) {
SpinRelease(BufMgrLock);
elog(FATAL,"Buffer in lookup table twice \n");
}
/* Buffer contents are currently invalid. Have
* to mark IO IN PROGRESS so no one fiddles with
* them until the read completes. If this routine
* has been called simply to allocate a buffer, no
* io will be attempted, so the flag isnt set.
*/
if (!inProgress) {
buf->flags |= BM_IO_IN_PROGRESS;
#ifdef HAS_TEST_AND_SET
Assert(S_LOCK_FREE(&(buf->io_in_progress_lock)));
S_LOCK(&(buf->io_in_progress_lock));
#endif /* HAS_TEST_AND_SET */
}
#ifdef BMTRACE
_bm_trace((reln->rd_rel->relisshared ? 0 : MyDatabaseId), reln->rd_id, blockNum, BufferDescriptorGetBuffer(buf), BMT_ALLOCNOTFND);
#endif /* BMTRACE */
SpinRelease(BufMgrLock);
return (buf);
}
/*
* WriteBuffer--
*
* Pushes buffer contents to disk if WriteMode is BUFFER_FLUSH_WRITE.
* Otherwise, marks contents as dirty.
*
* Assume that buffer is pinned. Assume that reln is
* valid.
*
* Side Effects:
* Pin count is decremented.
*/
#undef WriteBuffer
int
WriteBuffer(Buffer buffer)
{
BufferDesc *bufHdr;
if (WriteMode == BUFFER_FLUSH_WRITE) {
return (FlushBuffer (buffer, TRUE));
} else {
if (BufferIsLocal(buffer))
return WriteLocalBuffer(buffer, TRUE);
if (BAD_BUFFER_ID(buffer))
return(FALSE);
bufHdr = &BufferDescriptors[buffer-1];
SpinAcquire(BufMgrLock);
Assert(bufHdr->refcount > 0);
bufHdr->flags |= BM_DIRTY;
UnpinBuffer(bufHdr);
SpinRelease(BufMgrLock);
}
return(TRUE);
}
void
WriteBuffer_Debug(char *file, int line, Buffer buffer)
{
WriteBuffer(buffer);
if (ShowPinTrace && BufferIsLocal(buffer) && is_userbuffer(buffer)) {
BufferDesc *buf;
buf = &BufferDescriptors[buffer-1];
fprintf(stderr, "UNPIN(WR) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
buffer, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[buffer - 1], file, line);
}
}
/*
* DirtyBufferCopy() -- Copy a given dirty buffer to the requested
* destination.
*
* We treat this as a write. If the requested buffer is in the pool
* and is dirty, we copy it to the location requested and mark it
* clean. This routine supports the Sony jukebox storage manager,
* which agrees to take responsibility for the data once we mark
* it clean.
*
* NOTE: used by sony jukebox code in postgres 4.2 - ay 2/95
*/
void
DirtyBufferCopy(Oid dbid, Oid relid, BlockNumber blkno, char *dest)
{
BufferDesc *buf;
BufferTag btag;
btag.relId.relId = relid;
btag.relId.dbId = dbid;
btag.blockNum = blkno;
SpinAcquire(BufMgrLock);
buf = BufTableLookup(&btag);
if (buf == (BufferDesc *) NULL
|| !(buf->flags & BM_DIRTY)
|| !(buf->flags & BM_VALID)) {
SpinRelease(BufMgrLock);
return;
}
/* hate to do this holding the lock, but release and reacquire is slower */
memmove(dest, (char *) MAKE_PTR(buf->data), BLCKSZ);
buf->flags &= ~BM_DIRTY;
SpinRelease(BufMgrLock);
}
/*
* FlushBuffer -- like WriteBuffer, but force the page to disk.
*
* 'buffer' is known to be dirty/pinned, so there should not be a
* problem reading the BufferDesc members without the BufMgrLock
* (nobody should be able to change tags, flags, etc. out from under
* us).
*/
static int
FlushBuffer(Buffer buffer, bool release)
{
BufferDesc *bufHdr;
Oid bufdb;
Relation bufrel;
int status;
if (BufferIsLocal(buffer))
return FlushLocalBuffer(buffer, release);
if (BAD_BUFFER_ID(buffer))
return (STATUS_ERROR);
bufHdr = &BufferDescriptors[buffer-1];
bufdb = bufHdr->tag.relId.dbId;
Assert (bufdb == MyDatabaseId || bufdb == (Oid) NULL);
bufrel = RelationIdCacheGetRelation (bufHdr->tag.relId.relId);
Assert (bufrel != (Relation) NULL);
status = smgrflush(bufHdr->bufsmgr, bufrel, bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
if (status == SM_FAIL)
{
elog(WARN, "FlushBuffer: cannot flush block %u of the relation %.*s",
bufHdr->tag.blockNum,
NAMEDATALEN, bufrel->rd_rel->relname.data);
return (STATUS_ERROR);
}
SpinAcquire(BufMgrLock);
bufHdr->flags &= ~BM_DIRTY;
if ( release )
UnpinBuffer(bufHdr);
SpinRelease(BufMgrLock);
return(STATUS_OK);
}
/*
* WriteNoReleaseBuffer -- like WriteBuffer, but do not unpin the buffer
* when the operation is complete.
*
* We know that the buffer is for a relation in our private cache,
* because this routine is called only to write out buffers that
* were changed by the executing backend.
*/
int
WriteNoReleaseBuffer(Buffer buffer)
{
BufferDesc *bufHdr;
if (WriteMode == BUFFER_FLUSH_WRITE) {
return (FlushBuffer (buffer, FALSE));
} else {
if (BufferIsLocal(buffer))
return WriteLocalBuffer(buffer, FALSE);
if (BAD_BUFFER_ID(buffer))
return (STATUS_ERROR);
bufHdr = &BufferDescriptors[buffer-1];
SpinAcquire(BufMgrLock);
bufHdr->flags |= BM_DIRTY;
SpinRelease(BufMgrLock);
}
return(STATUS_OK);
}
#undef ReleaseAndReadBuffer
/*
* ReleaseAndReadBuffer -- combine ReleaseBuffer() and ReadBuffer()
* so that only one semop needs to be called.
*
*/
Buffer
ReleaseAndReadBuffer(Buffer buffer,
Relation relation,
BlockNumber blockNum)
{
BufferDesc *bufHdr;
Buffer retbuf;
if (BufferIsLocal(buffer)) {
Assert(LocalRefCount[-buffer - 1] > 0);
LocalRefCount[-buffer - 1]--;
} else {
if (BufferIsValid(buffer)) {
bufHdr = &BufferDescriptors[buffer-1];
Assert(PrivateRefCount[buffer - 1] > 0);
PrivateRefCount[buffer - 1]--;
if (PrivateRefCount[buffer - 1] == 0 &&
LastRefCount[buffer - 1] == 0) {
/* only release buffer if it is not pinned in previous ExecMain
level */
SpinAcquire(BufMgrLock);
bufHdr->refcount--;
if (bufHdr->refcount == 0) {
AddBufferToFreelist(bufHdr);
bufHdr->flags |= BM_FREE;
}
retbuf = ReadBufferWithBufferLock(relation, blockNum, true);
return retbuf;
}
}
}
return (ReadBuffer(relation, blockNum));
}
/*
* BufferSync -- Flush all dirty buffers in the pool.
*
* This is called at transaction commit time. It does the wrong thing,
* right now. We should flush only our own changes to stable storage,
* and we should obey the lock protocol on the buffer manager metadata
* as we do it. Also, we need to be sure that no other transaction is
* modifying the page as we flush it. This is only a problem for objects
* that use a non-two-phase locking protocol, like btree indices. For
* those objects, we would like to set a write lock for the duration of
* our IO. Another possibility is to code updates to btree pages
* carefully, so that writing them out out of order cannot cause
* any unrecoverable errors.
*
* I don't want to think hard about this right now, so I will try
* to come back to it later.
*/
static void
BufferSync()
{
int i;
Oid bufdb;
Oid bufrel;
Relation reln;
BufferDesc *bufHdr;
int status;
SpinAcquire(BufMgrLock);
for (i=0, bufHdr = BufferDescriptors; i < NBuffers; i++, bufHdr++) {
if ((bufHdr->flags & BM_VALID) && (bufHdr->flags & BM_DIRTY)) {
bufdb = bufHdr->tag.relId.dbId;
bufrel = bufHdr->tag.relId.relId;
if (bufdb == MyDatabaseId || bufdb == (Oid) 0) {
reln = RelationIdCacheGetRelation(bufrel);
/*
* We have to pin buffer to keep anyone from stealing it
* from the buffer pool while we are flushing it or
* waiting in WaitIO. It's bad for GetFreeBuffer in
* BufferAlloc, but there is no other way to prevent
* writing into disk block data from some other buffer,
* getting smgr status of some other block and
* clearing BM_DIRTY of ... - VAdim 09/16/96
*/
PinBuffer(bufHdr);
if (bufHdr->flags & BM_IO_IN_PROGRESS)
{
WaitIO(bufHdr, BufMgrLock);
UnpinBuffer(bufHdr);
if (bufHdr->flags & BM_IO_ERROR)
{
elog(WARN, "cannot write %u for %s",
bufHdr->tag.blockNum, bufHdr->sb_relname);
}
if (reln != (Relation)NULL)
RelationDecrementReferenceCount(reln);
continue;
}
/*
* If we didn't have the reldesc in our local cache, flush this
* page out using the 'blind write' storage manager routine. If
* we did find it, use the standard interface.
*/
#ifndef OPTIMIZE_SINGLE
SpinRelease(BufMgrLock);
#endif /* OPTIMIZE_SINGLE */
if (reln == (Relation) NULL) {
status = smgrblindwrt(bufHdr->bufsmgr, bufHdr->sb_dbname,
bufHdr->sb_relname, bufdb, bufrel,
bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
} else {
status = smgrwrite(bufHdr->bufsmgr, reln,
bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
}
#ifndef OPTIMIZE_SINGLE
SpinAcquire(BufMgrLock);
#endif /* OPTIMIZE_SINGLE */
UnpinBuffer(bufHdr);
if (status == SM_FAIL) {
bufHdr->flags |= BM_IO_ERROR;
elog(WARN, "cannot write %u for %s",
bufHdr->tag.blockNum, bufHdr->sb_relname);
}
/*
* What if someone has marked this buffer as DIRTY after
* smgr[blind]write but before SpinAcquire(BufMgrLock)
* ??? - vadim 01/16/97
*/
bufHdr->flags &= ~BM_DIRTY;
if (reln != (Relation)NULL)
RelationDecrementReferenceCount(reln);
}
}
}
SpinRelease(BufMgrLock);
LocalBufferSync();
}
/*
* WaitIO -- Block until the IO_IN_PROGRESS flag on 'buf'
* is cleared. Because IO_IN_PROGRESS conflicts are
* expected to be rare, there is only one BufferIO
* lock in the entire system. All processes block
* on this semaphore when they try to use a buffer
* that someone else is faulting in. Whenever a
* process finishes an IO and someone is waiting for
* the buffer, BufferIO is signaled (SignalIO). All
* waiting processes then wake up and check to see
* if their buffer is now ready. This implementation
* is simple, but efficient enough if WaitIO is
* rarely called by multiple processes simultaneously.
*
* ProcSleep atomically releases the spinlock and goes to
* sleep.
*
* Note: there is an easy fix if the queue becomes long.
* save the id of the buffer we are waiting for in
* the queue structure. That way signal can figure
* out which proc to wake up.
*/
#ifdef HAS_TEST_AND_SET
static void
WaitIO(BufferDesc *buf, SPINLOCK spinlock)
{
SpinRelease(spinlock);
S_LOCK(&(buf->io_in_progress_lock));
S_UNLOCK(&(buf->io_in_progress_lock));
SpinAcquire(spinlock);
}
#else /* HAS_TEST_AND_SET */
IpcSemaphoreId WaitIOSemId;
static void
WaitIO(BufferDesc *buf, SPINLOCK spinlock)
{
bool inProgress;
for (;;) {
/* wait until someone releases IO lock */
(*NWaitIOBackendP)++;
SpinRelease(spinlock);
IpcSemaphoreLock(WaitIOSemId, 0, 1);
SpinAcquire(spinlock);
inProgress = (buf->flags & BM_IO_IN_PROGRESS);
if (!inProgress) break;
}
}
/*
* SignalIO --
*/
static void
SignalIO(BufferDesc *buf)
{
/* somebody better be waiting. */
Assert( buf->refcount > 1);
IpcSemaphoreUnlock(WaitIOSemId, 0, *NWaitIOBackendP);
*NWaitIOBackendP = 0;
}
#endif /* HAS_TEST_AND_SET */
long NDirectFileRead; /* some I/O's are direct file access. bypass bufmgr */
long NDirectFileWrite; /* e.g., I/O in psort and hashjoin. */
void
PrintBufferUsage(FILE *statfp)
{
float hitrate;
if (ReadBufferCount==0)
hitrate = 0.0;
else
hitrate = (float)BufferHitCount * 100.0/ReadBufferCount;
fprintf(statfp, "!\t%ld blocks read, %ld blocks written, buffer hit rate = %.2f%%\n",
ReadBufferCount - BufferHitCount + NDirectFileRead,
BufferFlushCount + NDirectFileWrite,
hitrate);
}
void
ResetBufferUsage()
{
BufferHitCount = 0;
ReadBufferCount = 0;
BufferFlushCount = 0;
NDirectFileRead = 0;
NDirectFileWrite = 0;
}
/* ----------------------------------------------
* ResetBufferPool
*
* this routine is supposed to be called when a transaction aborts.
* it will release all the buffer pins held by the transaciton.
*
* ----------------------------------------------
*/
void
ResetBufferPool()
{
register int i;
for (i=1; i<=NBuffers; i++) {
if (BufferIsValid(i)) {
while(PrivateRefCount[i - 1] > 0) {
ReleaseBuffer(i);
}
}
LastRefCount[i - 1] = 0;
}
ResetLocalBufferPool();
}
/* -----------------------------------------------
* BufferPoolCheckLeak
*
* check if there is buffer leak
*
* -----------------------------------------------
*/
int
BufferPoolCheckLeak()
{
register int i;
void PrintBufferDescs();
for (i = 1; i <= NBuffers; i++) {
if (BufferIsValid(i)) {
elog(NOTICE, "buffer leak detected in BufferPoolCheckLeak()");
PrintBufferDescs();
return(1);
}
}
return(0);
}
/* ------------------------------------------------
* FlushBufferPool
*
* flush all dirty blocks in buffer pool to disk
*
* ------------------------------------------------
*/
void
FlushBufferPool(int StableMainMemoryFlag)
{
if (!StableMainMemoryFlag) {
BufferSync();
smgrcommit();
}
}
/*
* BufferIsValid --
* True iff the refcnt of the local buffer is > 0
* Note:
* BufferIsValid(InvalidBuffer) is False.
* BufferIsValid(UnknownBuffer) is False.
*/
bool
BufferIsValid(Buffer bufnum)
{
if (BufferIsLocal(bufnum))
return (bufnum >= -NLocBuffer && LocalRefCount[-bufnum - 1] > 0);
if (BAD_BUFFER_ID(bufnum))
return(false);
return ((bool)(PrivateRefCount[bufnum - 1] > 0));
}
/*
* BufferGetBlockNumber --
* Returns the block number associated with a buffer.
*
* Note:
* Assumes that the buffer is valid.
*/
BlockNumber
BufferGetBlockNumber(Buffer buffer)
{
Assert(BufferIsValid(buffer));
/* XXX should be a critical section */
if (BufferIsLocal(buffer))
return (LocalBufferDescriptors[-buffer-1].tag.blockNum);
else
return (BufferDescriptors[buffer-1].tag.blockNum);
}
/*
* BufferGetRelation --
* Returns the relation desciptor associated with a buffer.
*
* Note:
* Assumes buffer is valid.
*/
Relation
BufferGetRelation(Buffer buffer)
{
Relation relation;
Oid relid;
Assert(BufferIsValid(buffer));
Assert(!BufferIsLocal(buffer)); /* not supported for local buffers */
/* XXX should be a critical section */
relid = LRelIdGetRelationId(BufferDescriptors[buffer-1].tag.relId);
relation = RelationIdGetRelation(relid);
RelationDecrementReferenceCount(relation);
if (RelationHasReferenceCountZero(relation)) {
/*
elog(NOTICE, "BufferGetRelation: 0->1");
*/
RelationIncrementReferenceCount(relation);
}
return (relation);
}
/*
* BufferReplace
*
* Flush the buffer corresponding to 'bufHdr'
*
*/
static int
BufferReplace(BufferDesc *bufHdr, bool bufferLockHeld)
{
Relation reln;
Oid bufdb, bufrel;
int status;
if (!bufferLockHeld)
SpinAcquire(BufMgrLock);
/*
* first try to find the reldesc in the cache, if no luck,
* don't bother to build the reldesc from scratch, just do
* a blind write.
*/
bufdb = bufHdr->tag.relId.dbId;
bufrel = bufHdr->tag.relId.relId;
if (bufdb == MyDatabaseId || bufdb == (Oid) NULL)
reln = RelationIdCacheGetRelation(bufrel);
else
reln = (Relation) NULL;
SpinRelease(BufMgrLock);
if (reln != (Relation) NULL) {
status = smgrflush(bufHdr->bufsmgr, reln, bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
} else {
/* blind write always flushes */
status = smgrblindwrt(bufHdr->bufsmgr, bufHdr->sb_dbname,
bufHdr->sb_relname, bufdb, bufrel,
bufHdr->tag.blockNum,
(char *) MAKE_PTR(bufHdr->data));
}
if (status == SM_FAIL)
return (FALSE);
return (TRUE);
}
/*
* RelationGetNumberOfBlocks --
* Returns the buffer descriptor associated with a page in a relation.
*
* Note:
* XXX may fail for huge relations.
* XXX should be elsewhere.
* XXX maybe should be hidden
*/
BlockNumber
RelationGetNumberOfBlocks(Relation relation)
{
return
((relation->rd_islocal) ? relation->rd_nblocks :
smgrnblocks(relation->rd_rel->relsmgr, relation));
}
/*
* BufferGetBlock --
* Returns a reference to a disk page image associated with a buffer.
*
* Note:
* Assumes buffer is valid.
*/
Block
BufferGetBlock(Buffer buffer)
{
Assert(BufferIsValid(buffer));
if (BufferIsLocal(buffer))
return((Block)MAKE_PTR(LocalBufferDescriptors[-buffer-1].data));
else
return((Block)MAKE_PTR(BufferDescriptors[buffer-1].data));
}
/* ---------------------------------------------------------------------
* ReleaseRelationBuffers
*
* this function unmarks all the dirty pages of a relation
* in the buffer pool so that at the end of transaction
* these pages will not be flushed.
* XXX currently it sequentially searches the buffer pool, should be
* changed to more clever ways of searching.
* --------------------------------------------------------------------
*/
void
ReleaseRelationBuffers (Relation rdesc)
{
register int i;
int holding = 0;
BufferDesc *buf;
if ( rdesc->rd_islocal )
{
for (i = 0; i < NLocBuffer; i++)
{
buf = &LocalBufferDescriptors[i];
if ((buf->flags & BM_DIRTY) &&
(buf->tag.relId.relId == rdesc->rd_id))
{
buf->flags &= ~BM_DIRTY;
}
}
return;
}
for (i=1; i<=NBuffers; i++) {
buf = &BufferDescriptors[i-1];
if (!holding) {
SpinAcquire(BufMgrLock);
holding = 1;
}
if ((buf->flags & BM_DIRTY) &&
(buf->tag.relId.dbId == MyDatabaseId) &&
(buf->tag.relId.relId == rdesc->rd_id)) {
buf->flags &= ~BM_DIRTY;
if (!(buf->flags & BM_FREE)) {
SpinRelease(BufMgrLock);
holding = 0;
ReleaseBuffer(i);
}
}
}
if (holding)
SpinRelease(BufMgrLock);
}
/* ---------------------------------------------------------------------
* DropBuffers
*
* This function marks all the buffers in the buffer cache for a
* particular database as clean. This is used when we destroy a
* database, to avoid trying to flush data to disk when the directory
* tree no longer exists.
*
* This is an exceedingly non-public interface.
* --------------------------------------------------------------------
*/
void
DropBuffers(Oid dbid)
{
register int i;
BufferDesc *buf;
SpinAcquire(BufMgrLock);
for (i=1; i<=NBuffers; i++) {
buf = &BufferDescriptors[i-1];
if ((buf->tag.relId.dbId == dbid) && (buf->flags & BM_DIRTY)) {
buf->flags &= ~BM_DIRTY;
}
}
SpinRelease(BufMgrLock);
}
/* -----------------------------------------------------------------
* PrintBufferDescs
*
* this function prints all the buffer descriptors, for debugging
* use only.
* -----------------------------------------------------------------
*/
void
PrintBufferDescs()
{
int i;
BufferDesc *buf = BufferDescriptors;
if (IsUnderPostmaster) {
SpinAcquire(BufMgrLock);
for (i = 0; i < NBuffers; ++i, ++buf) {
elog(NOTICE, "[%02d] (freeNext=%d, freePrev=%d, relname=%.*s, \
blockNum=%d, flags=0x%x, refcount=%d %d)",
i, buf->freeNext, buf->freePrev, NAMEDATALEN,
buf->sb_relname, buf->tag.blockNum, buf->flags,
buf->refcount, PrivateRefCount[i]);
}
SpinRelease(BufMgrLock);
} else {
/* interactive backend */
for (i = 0; i < NBuffers; ++i, ++buf) {
printf("[%-2d] (%s, %d) flags=0x%x, refcnt=%d %ld)\n",
i, buf->sb_relname, buf->tag.blockNum,
buf->flags, buf->refcount, PrivateRefCount[i]);
}
}
}
void
PrintPinnedBufs()
{
int i;
BufferDesc *buf = BufferDescriptors;
SpinAcquire(BufMgrLock);
for (i = 0; i < NBuffers; ++i, ++buf) {
if (PrivateRefCount[i] > 0)
elog(NOTICE, "[%02d] (freeNext=%d, freePrev=%d, relname=%.*s, \
blockNum=%d, flags=0x%x, refcount=%d %d)\n",
i, buf->freeNext, buf->freePrev, NAMEDATALEN, buf->sb_relname,
buf->tag.blockNum, buf->flags,
buf->refcount, PrivateRefCount[i]);
}
SpinRelease(BufMgrLock);
}
/*
* BufferPoolBlowaway
*
* this routine is solely for the purpose of experiments -- sometimes
* you may want to blowaway whatever is left from the past in buffer
* pool and start measuring some performance with a clean empty buffer
* pool.
*/
void
BufferPoolBlowaway()
{
register int i;
BufferSync();
for (i=1; i<=NBuffers; i++) {
if (BufferIsValid(i)) {
while(BufferIsValid(i))
ReleaseBuffer(i);
}
BufTableDelete(&BufferDescriptors[i-1]);
}
}
#undef IncrBufferRefCount
#undef ReleaseBuffer
void
IncrBufferRefCount(Buffer buffer)
{
if (BufferIsLocal(buffer)) {
Assert(LocalRefCount[-buffer - 1] >= 0);
LocalRefCount[-buffer - 1]++;
} else {
Assert(!BAD_BUFFER_ID(buffer));
Assert(PrivateRefCount[buffer - 1] >= 0);
PrivateRefCount[buffer - 1]++;
}
}
/*
* ReleaseBuffer -- remove the pin on a buffer without
* marking it dirty.
*
*/
int
ReleaseBuffer(Buffer buffer)
{
BufferDesc *bufHdr;
if (BufferIsLocal(buffer)) {
Assert(LocalRefCount[-buffer - 1] > 0);
LocalRefCount[-buffer - 1]--;
return (STATUS_OK);
}
if (BAD_BUFFER_ID(buffer))
return(STATUS_ERROR);
bufHdr = &BufferDescriptors[buffer-1];
Assert(PrivateRefCount[buffer - 1] > 0);
PrivateRefCount[buffer - 1]--;
if (PrivateRefCount[buffer - 1] == 0 && LastRefCount[buffer - 1] == 0) {
/* only release buffer if it is not pinned in previous ExecMain
levels */
SpinAcquire(BufMgrLock);
bufHdr->refcount--;
if (bufHdr->refcount == 0) {
AddBufferToFreelist(bufHdr);
bufHdr->flags |= BM_FREE;
}
SpinRelease(BufMgrLock);
}
return(STATUS_OK);
}
void
IncrBufferRefCount_Debug(char *file, int line, Buffer buffer)
{
IncrBufferRefCount(buffer);
if (ShowPinTrace && !BufferIsLocal(buffer) && is_userbuffer(buffer)) {
BufferDesc *buf = &BufferDescriptors[buffer-1];
fprintf(stderr, "PIN(Incr) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
buffer, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[buffer - 1], file, line);
}
}
void
ReleaseBuffer_Debug(char *file, int line, Buffer buffer)
{
ReleaseBuffer(buffer);
if (ShowPinTrace && !BufferIsLocal(buffer) && is_userbuffer(buffer)) {
BufferDesc *buf = &BufferDescriptors[buffer-1];
fprintf(stderr, "UNPIN(Rel) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
buffer, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[buffer - 1], file, line);
}
}
int
ReleaseAndReadBuffer_Debug(char *file,
int line,
Buffer buffer,
Relation relation,
BlockNumber blockNum)
{
bool bufferValid;
Buffer b;
bufferValid = BufferIsValid(buffer);
b = ReleaseAndReadBuffer(buffer, relation, blockNum);
if (ShowPinTrace && bufferValid && BufferIsLocal(buffer)
&& is_userbuffer(buffer)) {
BufferDesc *buf = &BufferDescriptors[buffer-1];
fprintf(stderr, "UNPIN(Rel&Rd) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
buffer, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[buffer - 1], file, line);
}
if (ShowPinTrace && BufferIsLocal(buffer) && is_userbuffer(buffer)) {
BufferDesc *buf = &BufferDescriptors[b-1];
fprintf(stderr, "PIN(Rel&Rd) %ld relname = %s, blockNum = %d, \
refcount = %ld, file: %s, line: %d\n",
b, buf->sb_relname, buf->tag.blockNum,
PrivateRefCount[b - 1], file, line);
}
return b;
}
#ifdef BMTRACE
/*
* trace allocations and deallocations in a circular buffer in
* shared memory. check the buffer before doing the allocation,
* and die if there's anything fishy.
*/
_bm_trace(Oid dbId, Oid relId, int blkNo, int bufNo, int allocType)
{
static int mypid = 0;
long start, cur;
bmtrace *tb;
if (mypid == 0)
mypid = getpid();
start = *CurTraceBuf;
if (start > 0)
cur = start - 1;
else
cur = BMT_LIMIT - 1;
for (;;) {
tb = &TraceBuf[cur];
if (tb->bmt_op != BMT_NOTUSED) {
if (tb->bmt_buf == bufNo) {
if ((tb->bmt_op == BMT_DEALLOC)
|| (tb->bmt_dbid == dbId && tb->bmt_relid == relId
&& tb->bmt_blkno == blkNo))
goto okay;
/* die holding the buffer lock */
_bm_die(dbId, relId, blkNo, bufNo, allocType, start, cur);
}
}
if (cur == start)
goto okay;
if (cur == 0)
cur = BMT_LIMIT - 1;
else
cur--;
}
okay:
tb = &TraceBuf[start];
tb->bmt_pid = mypid;
tb->bmt_buf = bufNo;
tb->bmt_dbid = dbId;
tb->bmt_relid = relId;
tb->bmt_blkno = blkNo;
tb->bmt_op = allocType;
*CurTraceBuf = (start + 1) % BMT_LIMIT;
}
_bm_die(Oid dbId, Oid relId, int blkNo, int bufNo,
int allocType, long start, long cur)
{
FILE *fp;
bmtrace *tb;
int i;
tb = &TraceBuf[cur];
if ((fp = fopen("/tmp/death_notice", "w")) == (FILE *) NULL)
elog(FATAL, "buffer alloc trace error and can't open log file");
fprintf(fp, "buffer alloc trace detected the following error:\n\n");
fprintf(fp, " buffer %d being %s inconsistently with a previous %s\n\n",
bufNo, (allocType == BMT_DEALLOC ? "deallocated" : "allocated"),
(tb->bmt_op == BMT_DEALLOC ? "deallocation" : "allocation"));
fprintf(fp, "the trace buffer contains:\n");
i = start;
for (;;) {
tb = &TraceBuf[i];
if (tb->bmt_op != BMT_NOTUSED) {
fprintf(fp, " [%3d]%spid %d buf %2d for <%d,%d,%d> ",
i, (i == cur ? " ---> " : "\t"),
tb->bmt_pid, tb->bmt_buf,
tb->bmt_dbid, tb->bmt_relid, tb->bmt_blkno);
switch (tb->bmt_op) {
case BMT_ALLOCFND:
fprintf(fp, "allocate (found)\n");
break;
case BMT_ALLOCNOTFND:
fprintf(fp, "allocate (not found)\n");
break;
case BMT_DEALLOC:
fprintf(fp, "deallocate\n");
break;
default:
fprintf(fp, "unknown op type %d\n", tb->bmt_op);
break;
}
}
i = (i + 1) % BMT_LIMIT;
if (i == start)
break;
}
fprintf(fp, "\noperation causing error:\n");
fprintf(fp, "\tpid %d buf %d for <%d,%d,%d> ",
getpid(), bufNo, dbId, relId, blkNo);
switch (allocType) {
case BMT_ALLOCFND:
fprintf(fp, "allocate (found)\n");
break;
case BMT_ALLOCNOTFND:
fprintf(fp, "allocate (not found)\n");
break;
case BMT_DEALLOC:
fprintf(fp, "deallocate\n");
break;
default:
fprintf(fp, "unknown op type %d\n", allocType);
break;
}
(void) fclose(fp);
kill(getpid(), SIGILL);
}
#endif /* BMTRACE */
void
BufferRefCountReset(int *refcountsave)
{
int i;
for (i=0; i<NBuffers; i++) {
refcountsave[i] = PrivateRefCount[i];
LastRefCount[i] += PrivateRefCount[i];
PrivateRefCount[i] = 0;
}
}
void
BufferRefCountRestore(int *refcountsave)
{
int i;
for (i=0; i<NBuffers; i++) {
PrivateRefCount[i] = refcountsave[i];
LastRefCount[i] -= refcountsave[i];
refcountsave[i] = 0;
}
}
int SetBufferWriteMode (int mode)
{
int old;
old = WriteMode;
WriteMode = mode;
return (old);
}
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