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windows-nt/Source/XPSP1/NT/com/svcdlls/trksvcs/trkwks/log.cxx

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2020-09-26 03:20:57 -05:00
// Copyright (c) 1996-1999 Microsoft Corporation
//+-------------------------------------------------------------------------
//
// Microsoft Windows
//
// File: log.cxx
//
// Contents: Implementation of Tracking (Workstation) Service log of moves.
//
// Classes: CLog
//
// Functions:
//
// Notes: The log is composed of a header and a linked-list of move
// notification entries. This structure is provided by the
// CLogFile class.
//
//--------------------------------------------------------------------------
#include "pch.cxx"
#pragma hdrstop
#include "trkwks.hxx"
//+----------------------------------------------------------------------------
//
// Method: Initialize
//
// Synopsis: Initialize a CLog object.
//
// Arguments: [pLogCallback] (in)
// A PLogCallback object, which we'll call when we have new
// data.
// [pcTrkWksConfiguration] (in)
// Configuration parameters for the log.
// [pcLogFile] (in)
// The object representing the log file.
//
// Returns: None
//
//+----------------------------------------------------------------------------
void
CLog::Initialize( PLogCallback *pLogCallback,
const CTrkWksConfiguration *pcTrkWksConfiguration,
CLogFile *pcLogFile )
{
LogInfo loginfo;
// Save the inputs
TrkAssert( NULL != pcLogFile || NULL != _pcLogFile );
if( NULL != pcLogFile )
_pcLogFile = pcLogFile;
TrkAssert( NULL != pcTrkWksConfiguration || NULL != _pcTrkWksConfiguration );
if( NULL != pcTrkWksConfiguration )
_pcTrkWksConfiguration = pcTrkWksConfiguration;
TrkAssert( NULL != pLogCallback || NULL != _pLogCallback );
if( NULL != pLogCallback )
_pLogCallback = pLogCallback;
// Read the log info from the log header.
_pcLogFile->ReadExtendedHeader( CLOG_LOGINFO_START, &loginfo, CLOG_LOGINFO_LENGTH );
// If the log hadn't been shut down properly, it's been fixed by now, but
// we can't trust the loginfo we just read from the header. We also
// can't trust it if it doesn't make sense. So if for some reason we
// can't trust it, we'll recalculate it (this can be slow, though).
if( !_pcLogFile->IsShutdown() || loginfo.ilogStart == loginfo.ilogEnd )
{
_fDirty = TRUE;
loginfo = QueryLogInfo();
}
// Save the now-good information.
_loginfo = loginfo;
} // CLog::Initialize()
//+----------------------------------------------------------------------------
//
// Method: QueryLogInfo
//
// Synopsis: Read the log entries and determine the indices and sequence
// numbers.
//
// Arguments: None
//
// Returns: A LogInfo structure
//
//+----------------------------------------------------------------------------
LogInfo
CLog::QueryLogInfo()
{
SequenceNumber seqMin, seqMax;
ULONG cEntries;
LogIndex ilogMin, ilogMax, ilogEntry;
LogInfo loginfo;
LogMoveNotification lmn;
BOOL fLogEmpty = TRUE;
LogEntryHeader entryheader;
TrkLog(( TRKDBG_LOG, TEXT("Reading log to determine correct indices") ));
// ------------
// Scan the log
// ------------
seqMin = 0;
seqMax = 0;
cEntries = _pcLogFile->NumEntriesInFile();
ilogMin = 0;
ilogMax = cEntries - 1;
// Scan the log and look at the sequence numbers to find
// the start and end indices.
for( ilogEntry = 0; ilogEntry < cEntries; ilogEntry++ )
{
_pcLogFile->ReadMoveNotification( ilogEntry, &lmn );
if( LE_TYPE_MOVE == lmn.type )
{
SequenceNumber seq = lmn.seq;
// If this is the first move notification that we've
// found, then it is currently both the min and the max.
if( fLogEmpty )
{
fLogEmpty = FALSE;
seqMin = seqMax = seq;
ilogMin = ilogMax = seq;
}
// If this isn't the first entry we've found, then see
// if it is a new min or max.
else
{
if( seq <= seqMin )
{
seqMin = seq;
ilogMin = ilogEntry;
}
else if( seq >= seqMax )
{
seqMax = seq;
ilogMax = ilogEntry;
}
}
} // if( LE_TYPE_MOVE == _pcLogFile->ReadMoveNotification( ilogEntry )->type )
} // for( ilogEntry = 0; ilogEntry < cEntries; ilogEntry++ )
// -------------------------------
// Determine the log indices, etc.
// -------------------------------
// Were there any entries in the log?
if( fLogEmpty )
{
// No, the log is empty.
loginfo.ilogStart = loginfo.ilogWrite = 0;
loginfo.ilogLast = loginfo.ilogEnd = cEntries - 1;
}
else
{
// Yes, the log is non-empty.
// Point the start index to the oldest move in the log.
loginfo.ilogStart = ilogMin;
// Point the last index to the oldest move in the log,
// and point the write index to the entry after that
// (which is the first available entry).
loginfo.ilogLast = loginfo.ilogWrite = ilogMax;
_pcLogFile->AdjustLogIndex( &loginfo.ilogWrite, 1 );
// The write & start indices should only be the same
// in an empty log. We know we're not empty at this point,
// so if they're the same, then the start index must have
// actually advanced (otherwise, the write index wouldn't be
// allowed to be here). So we advance the start index.
if( loginfo.ilogWrite == loginfo.ilogStart )
{
_pcLogFile->AdjustLogIndex( &loginfo.ilogStart, 1 );
}
} // if( fLogEmpty ) ... else
// The end if the log is just before the start in the circular list.
loginfo.ilogEnd = loginfo.ilogStart;
_pcLogFile->AdjustLogIndex( &loginfo.ilogEnd, -1 );
// The read index and next available
// sequence number are stored in the last entry header.
entryheader = _pcLogFile->ReadEntryHeader( loginfo.ilogLast );
loginfo.ilogRead = entryheader.ilogRead;
loginfo.seqNext = entryheader.seq;
// The sequence number of the entry last read is one below the sequence number
// of the entry currently at the read pointer. If everything is read
// (the read pointer is beyond the last entry) or if the entry at the
// read pointer is invalid, then we'll assume that the last read seq
// number is seqNext-1.
_pcLogFile->ReadMoveNotification( loginfo.ilogRead, &lmn );
loginfo.seqLastRead = ( loginfo.ilogWrite != loginfo.ilogRead && LE_TYPE_MOVE == lmn.type )
? lmn.seq - 1 : loginfo.seqNext-1;
TrkAssert( seqMax + 1 == loginfo.seqNext || 0 == loginfo.seqNext );
TrkAssert( loginfo.seqLastRead < loginfo.seqNext );
return( loginfo );
} // CLog::QueryLogInfo()
//+----------------------------------------------------------------------------
//
// Method: GenerateDefaultLogInfo
//
// Synopsis: Calculates the default _loginfo structure, based only on
// the last index. This requires no calls to CLogFile.
//
// Arguments: [ilogEnd] (in)
// The index of the last entry in the logfile.
//
// Returns: None
//
//+----------------------------------------------------------------------------
void
CLog::GenerateDefaultLogInfo( LogIndex ilogEnd )
{
SetDirty( TRUE ); // Must be called before changing _loginfo
_loginfo.ilogStart = _loginfo.ilogWrite = _loginfo.ilogRead = 0;
_loginfo.ilogLast = _loginfo.ilogEnd = ilogEnd;
_loginfo.seqNext = 0;
_loginfo.seqLastRead = _loginfo.seqNext - 1;
}
//+----------------------------------------------------------------------------
//
// Method: Flush
//
// Synopsis: Write the _loginfo structure to the CLogFile.
//
// Arguments: None
//
// Returns: None
//
//+----------------------------------------------------------------------------
void
CLog::Flush( )
{
if( _fDirty )
_pcLogFile->WriteExtendedHeader( CLOG_LOGINFO_START, &_loginfo, CLOG_LOGINFO_LENGTH );
SetDirty( FALSE );
}
//+----------------------------------------------------------------------------
//
// Method: ExpandLog
//
// Synopsis: Grow the log file, initialize the new entries, and update
// our indices. We determine how much to grow based on
// configuration parameters in CTrkWksConfiguration.
//
// Arguments: None.
//
// Returns: None.
//
//+----------------------------------------------------------------------------
void
CLog::ExpandLog()
{
TrkAssert( !_pcLogFile->IsMaxSize() );
TrkAssert( IsFull() );
SetDirty( TRUE ); // Must be called before changing _loginfo
// Grow the file, initialize the new log entries, and link the new
// entries into the existing linked list. We only need to tell
// the CLogFile where the start of the circular linked-list is.
_pcLogFile->Expand( _loginfo.ilogStart );
// Update the end pointer.
_loginfo.ilogEnd = _loginfo.ilogStart;
_pcLogFile->AdjustLogIndex( &_loginfo.ilogEnd, -1 );
} // CLog::Expand
//+----------------------------------------------------------------------------
//
// Method: Read
//
// Synopsis: Read zero or more entries from the log, starting at the
// Read index. Read until we reach the end of the data in
// the log, or until we've read as many as the caller
// requested.
//
// Note that we don't update the read index after this read,
// the caller must call Seek to accomplish this. This was done
// so that if the caller encountered an error after the Read,
// the log would still be unchanged for a retry.
//
// Arguments: [pNotifications] (in/out)
// Receives the move notification records.
// [pseqFirst] (out)
// The sequence number of the first notification returned.
// [pcRead] (in/out)
// (in) the number of notifications desired
// (out) the number of notifications actually read
// If the number read is less than the number requested,
// the caller may assume that there are no more entries
// to read.
//
// Returns: None
//
//+----------------------------------------------------------------------------
void
CLog::Read(CObjId rgobjidCurrent[],
CDomainRelativeObjId rgdroidBirth[],
CDomainRelativeObjId rgdroidNew[],
SequenceNumber *pseqFirst,
IN OUT ULONG *pcRead)
{
// --------------
// Initialization
// --------------
LogIndex ilogEntry;
ULONG cRead = 0;
ULONG iRead = 0;
SequenceNumber seqExpected = 0;
ilogEntry = _loginfo.ilogRead;
// ----------------
// Read the entries
// ----------------
// We can NOOP if the call request no entries, or if there
// are no entries in the log, or if all the entries have
// been read already.
if( *pcRead != 0 && !IsEmpty() && !IsRead() )
{
LogMoveNotification lmn;
// There are entries which we can read.
// Save the sequence number of the first entry that
// we'll return to the caller.
_pcLogFile->ReadMoveNotification( ilogEntry, &lmn );
*pseqFirst = lmn.seq;
seqExpected = lmn.seq;
// Read the entries from the log in order, validating
// the sequence numbers as we go.
do
{
// Copy the move information into the caller's buffer.
// ReadMoveNotification doesn't make the CLogFile dirty.
_pcLogFile->ReadMoveNotification( ilogEntry, &lmn );
TrkAssert( seqExpected == lmn.seq );
if( seqExpected != lmn.seq )
{
TrkLog(( TRKDBG_ERROR, TEXT("Invalid sequence numbers reading log (%d, %d)"),
seqExpected, lmn.seq ));
TrkRaiseException( TRK_E_CORRUPT_LOG );
}
seqExpected++;
rgobjidCurrent[iRead] = lmn.objidCurrent;
rgdroidNew[iRead] = lmn.droidNew;
rgdroidBirth[iRead] = lmn.droidBirth;
cRead++;
iRead++;
// Move on to the next entry.
_pcLogFile->AdjustLogIndex( &ilogEntry, 1 );
// Continue as long as there's still room in the caller's buffer
// and we haven't reached the last entry.
} while ( cRead < *pcRead && ilogEntry != _loginfo.ilogWrite );
}
*pcRead = cRead;
} // CLog:Read()
//+----------------------------------------------------------------------------
//
// CLog::DoSearch
//
// This is a private worker method that searches the log, either for a
// sequence number, or an object ID (which to use is determined by the
// fSearchUsingSeq parameter).
//
// The log entry data and index are returned.
//
//+----------------------------------------------------------------------------
// NOTE! *piFound is not modified if Search returns FALSE
BOOL
CLog::DoSearch( BOOL fSearchUsingSeq,
SequenceNumber seqSearch, // Use this if fSearchUsingSeq
const CObjId &objidCurrent, // Use this if !fSearchUsingSeq
ULONG *piFound,
CDomainRelativeObjId *pdroidNew,
CMachineId *pmcidNew,
CDomainRelativeObjId *pdroidBirth )
{
BOOL fFound = FALSE;
BOOL fFirstPass = TRUE;
SequenceNumber seqPrevious = 0;
#if DBG
LONG l = GetTickCount();
#endif
// Only bother to look if there's entries in the log.
if (!IsEmpty())
{
// Determine the max entries in the log so that we can
// detect if we're in an infinite loop.
ULONG cEntriesMax = _pcLogFile->NumEntriesInFile();
ULONG cEntryCurrent = 0;
LogIndex ilogSearch = _loginfo.ilogWrite;
// Search from the end, until we find what we're looking for,
// or we reach the beginning of the log.
// It's important that we search backwards because of tunneling.
// Here's the scenario ... An object is moved from machine A to
// B, quickly back to A, and then to C. Since it reappeared on A
// quickly after it first disappeared, tunneling will give it the
// same Object ID that it had before. So when it moves to C,
// we end up with two entries in the log for the object. We want
// to search backwards so that we see the move to C, not the move
// to B.
while( !fFound && ilogSearch != _loginfo.ilogStart )
{
// Check to see if we're in an infinite loop.
if( ++cEntryCurrent > cEntriesMax )
{
TrkLog((TRKDBG_ERROR, TEXT("Corrupt log file: cycle found during search")));
TrkRaiseException( TRK_E_CORRUPT_LOG );
}
// Read the previous entry.
_pcLogFile->AdjustLogIndex( &ilogSearch, -1 );
LogMoveNotification lmnSearch;
_pcLogFile->ReadMoveNotification( ilogSearch, &lmnSearch );
// If this isn't a move entry, then there's nothing left to search.
if( LE_TYPE_MOVE != lmnSearch.type )
goto Exit;
// Or, if this isn't the first pass, ensure that the sequence numbers
// are consequtive.
else if( !fFirstPass )
{
fFirstPass = FALSE;
TrkAssert( seqPrevious - 1 == lmnSearch.seq );
if( seqPrevious - 1 != lmnSearch.seq )
{
TrkLog(( TRKDBG_ERROR, TEXT("Corrupt log file: non-consequtive sequence numbers (%d %d)"),
seqPrevious, lmnSearch.seq ));
TrkRaiseException( TRK_E_CORRUPT_LOG );
}
}
// Is this the entry we're looking for?
if( fSearchUsingSeq && seqSearch == lmnSearch.seq
||
!fSearchUsingSeq && objidCurrent == lmnSearch.objidCurrent )
{
if( NULL != piFound )
*piFound = ilogSearch;
if( NULL != pdroidNew )
{
*pdroidNew = lmnSearch.droidNew;
*pmcidNew = lmnSearch.mcidNew;
*pdroidBirth = lmnSearch.droidBirth;
}
fFound = TRUE;
}
} // while( !fFound && ilogSearch != _loginfo.ilogStart )
} // if (!IsEmpty())
Exit:
return( fFound );
} // CLog::DoSearch
//+----------------------------------------------------------------------------
//
// Method: Search
//
// Synopsis: Search the log for an Object ID. Once found, return that
// entry's LinkData and BirthID.
//
// Arguments: [droidCurrent] (in)
// The ObjectID for which to search.
// [pdroidNew] (out)
// The entry's LinkData
// [pdroidBirth] (out)
// The entry's Birth ID.
//
// Returns: None
//
//+----------------------------------------------------------------------------
BOOL
CLog::Search( const CObjId &objidCurrent,
CDomainRelativeObjId *pdroidNew,
CMachineId *pmcidNew,
CDomainRelativeObjId *pdroidBirth )
{
ULONG iFound;
return DoSearch( FALSE, // => Use objidCurrent
0, // Therefore, we don't need a seq number
objidCurrent,
&iFound,
pdroidNew,
pmcidNew,
pdroidBirth );
} // CLog::Search( CDomainRelativeObjId& ...
//+----------------------------------------------------------------------------
//
// Method: CLog::Search
//
// Synopsis: Search the log for the entry with a particular sequence
// number.
//
// Arguments: [seqSearch] (in)
// The sequence number for which to search.
// [piFound] (out)
// The index with this sequence number (if found).
//
// Returns: [BOOL]
// TRUE if found, FALSE otherwise.
//
//+----------------------------------------------------------------------------
BOOL
CLog::Search( SequenceNumber seqSearch, ULONG *piFound )
{
CObjId oidNull;
return DoSearch( TRUE, // => Use seqSearch
seqSearch,
oidNull, // We don't need to pass an objid
piFound,
// And we don't need out-droids & mcid.
NULL, NULL, NULL );
} // CLog::Search( SequenceNumber ...
//+----------------------------------------------------------------------------
//
// Method: Append
//
// Synopsis: Add a move notification to the log. If the log is full,
// either overwrite an old entry, or grow the log.
//
// Arguments: [droidCurrent] (in)
// The link information of the file which was moved.
// [droidNew] (in)
// The link information of the new file.
// [droidBirth] (in)
// The Birth ID of the file.
//
// Returns: None
//
//+----------------------------------------------------------------------------
// Perf optimization: Tell the caller if the log is now full. The service can then lazily
// expand it, hopefully before the next move occurs.
void
CLog::Append(const CVolumeId &volidCurrent,
const CObjId &objidCurrent,
const CDomainRelativeObjId &droidNew,
const CMachineId &mcidNew,
const CDomainRelativeObjId &droidBirth)
{
LogMoveNotification lmnWrite;
CFILETIME cftNow; // Defaults to current UTC
BOOL fAdvanceStart = FALSE;
LogEntryHeader entryheader;
LogInfo loginfoZero;
// -----------------
// Handle a Full Log
// -----------------
if( IsFull() )
{
// Is the log already maxed? If so, we wrap.
if( _pcLogFile->IsMaxSize() )
{
fAdvanceStart = TRUE;
TrkLog(( TRKDBG_VOLUME, TEXT("Wrapping log") ));
}
// Otherwise, we'll handle it by growing the log file.
else
ExpandLog();
}
// -------------------------
// Write the data to the log
// -------------------------
// Before anything else, we must mark ourselves dirty. If the logfile is
// currently in the ProperShutdown state, this SetDirty call will take it
// out of that state and do a flush.
SetDirty( TRUE );
// Mark our loginfo cache in the header as invalid,
// in case we get pre-empted.
memset( &loginfoZero, 0, sizeof(loginfoZero) );
_pcLogFile->WriteExtendedHeader( CLOG_LOGINFO_START, &loginfoZero, CLOG_LOGINFO_LENGTH );
// Collect the move-notification information
memset( &lmnWrite, 0, sizeof(lmnWrite) );
lmnWrite.seq = _loginfo.seqNext;
lmnWrite.type = LE_TYPE_MOVE;
lmnWrite.objidCurrent = objidCurrent;
lmnWrite.droidNew = droidNew;
lmnWrite.mcidNew = mcidNew;
lmnWrite.droidBirth = droidBirth;
lmnWrite.DateWritten = TrkTimeUnits( cftNow );
// Collect the entry header information
memset( &entryheader, 0, sizeof(entryheader) );
entryheader.ilogRead = _loginfo.ilogRead;
entryheader.seq = _loginfo.seqNext + 1; // Reflect that we'll increment after the write
// Write everything to the log (this will do a flush). If this fails, it will raise.
_pcLogFile->WriteMoveNotification( _loginfo.ilogWrite, lmnWrite, entryheader );
// Update the sequence number and last & write indices now that we
// know the write was successful (all the way to the disk).
_loginfo.seqNext++;
_loginfo.ilogLast = _loginfo.ilogWrite;
_pcLogFile->AdjustLogIndex( &_loginfo.ilogWrite, 1 );
// Do we need to advance the start pointer?
// We save this for the end, because it may cause us to access
// the disk.
if( fAdvanceStart )
{
// We're about to advance the start index, and thus effectively
// lose an entry. If the read index points to the same place,
// then we should advance it as well.
if( _loginfo.ilogStart == _loginfo.ilogRead )
_pcLogFile->AdjustLogIndex( &_loginfo.ilogRead, 1 );
// Advance the start/end indices.
_pcLogFile->AdjustLogIndex( &_loginfo.ilogEnd, 1 );
_pcLogFile->AdjustLogIndex( &_loginfo.ilogStart, 1 );
}
TrkLog(( TRKDBG_VOLUME, TEXT("Appended %s to log (seq=%d)"),
(const TCHAR*)CDebugString(objidCurrent), lmnWrite.seq ));
// Notify the callback object that there is data available.
// Note: This must be the last operation of this method.
_pLogCallback->OnEntriesAvailable();
}
//+----------------------------------------------------------------------------
//
// Method: Seek( SequenceNumber ...
//
// Synopsis: Moves the Read index to a the log entry with the specified
// sequence number. If the seq number doesn't exist, we back
// up to the start of the log.
//
// If this seek causes us to back up the Read index, we notify
// the PLogCallback object, since we now have data available
// to read.
//
// Arguments: [seqSeek] (in)
// The sequence number to which to seek.
//
// Returns: [BOOL]
// TRUE if the sequence number was found, FALSE otherwise.
//
//+----------------------------------------------------------------------------
BOOL
CLog::Seek( const SequenceNumber &seqSeek )
{
BOOL fFound = FALSE;
SequenceNumber seqReadOriginal, seqReadNew;
LogMoveNotification lmn;
LogIndex ilogSearch = 0;
// Are we seeking to the end of the log?
if( seqSeek == _loginfo.seqNext )
{
// We found what we're looking for.
fFound = TRUE;
// Are we already at seqNext?
if( !IsRead() )
{
// No, update the read index.
SetDirty( TRUE );
_loginfo.ilogRead = _loginfo.ilogWrite;
}
goto Exit;
}
// If the log is empty, then there's nothing we need do.
if( IsEmpty() )
goto Exit;
// Or, if the caller wishes to seek beyond the end of our log, then
// again there's nothing to do. This could be the case, for example,
// if the log has been restored.
if( seqSeek >= _loginfo.seqNext )
goto Exit;
// Keep track of the current seq number at the read pointer, so that
// we can later tell if it's necessary to notify the client that
// there is "new" data.
if( IsRead() )
{
seqReadOriginal = _loginfo.seqNext;
}
else
{
_pcLogFile->ReadMoveNotification( _loginfo.ilogRead, &lmn );
seqReadOriginal = lmn.seq;
}
// If this seq number is in the log, set the Read index
// to it. Otherwise set it to the oldest entry in the
// log (that's the best we can do).
SetDirty( TRUE ); // Must be called before changing _loginfo
if( fFound = Search( seqSeek, &ilogSearch ))
_loginfo.ilogRead = ilogSearch;
else
_loginfo.ilogRead = _loginfo.ilogStart;
// Calculate the sequence number of the entry now at the read pointer, and
// use it to cache the seq number of the last-read entry (recall that
// the read pointer points to the next entry to be read, not the
// last entry read).
if( IsRead() )
{
seqReadNew = _loginfo.seqNext;
}
else
{
_pcLogFile->ReadMoveNotification( _loginfo.ilogRead, &lmn );
seqReadNew = lmn.seq;
}
_loginfo.seqLastRead = seqReadNew - 1; // We already set _fDirty
// Update the entry headers with the new read pointer.
WriteEntryHeader();
// If we've backed up the read pointer, notify the registered callback.
if ( seqReadOriginal > seqReadNew )
{
// Note: This must be the last operation of this method.
_pLogCallback->OnEntriesAvailable();
}
// ----
// Exit
// ----
Exit:
return( fFound );
} // CLog::Seek( SequenceNumber ...
//+----------------------------------------------------------------------------
//
// Method: Seek( origin ...
//
// Synopsis: Move the read pointer relative to an origin (begin, current, end).
//
// There are two differences between a CLog seek and a file seek:
// - If you seek from the beginning (SEEK_SET), and seek beyond the
// end of the log, the pointer is wrapped, rather than growing
// the log.
// - If you seek from the current location (SEEK_CUR), and seek
// beyond the end of the log, the log is not grown, and there
// is no wrap, the index simply stops there (either at _loginfo.ilogWrite
// or _loginfo.ilogStart).
//
// Arguments: [origin]
// Must be either SEEK_SET or SEEK_CUR (there is currently no
// support for SEEK_END).
// [iSeek]
// The amount to move relative to the origin.
//
// Returns: None
//
//+----------------------------------------------------------------------------
void
CLog::Seek( int origin, int iSeek )
{
SequenceNumber seqReadOriginal = 0, seqReadNew = 0;
LogMoveNotification lmn;
// Early exit if there's nothing to do
if( IsEmpty() )
goto Exit;
// Keep track of where we are now, so that we can determine if
// we've gone overall backwards or forwards.
if( IsRead() )
{
seqReadOriginal = _loginfo.seqNext;
}
else
{
_pcLogFile->ReadMoveNotification( _loginfo.ilogRead, &lmn );
seqReadOriginal = lmn.seq;
}
// Seek based on the origin.
switch( origin )
{
case SEEK_SET:
{
// Advance from the start index.
LogIndex ilogRead = _loginfo.ilogStart;
_pcLogFile->AdjustLogIndex( &ilogRead, iSeek );
SetDirty( TRUE ); // Must be called before changing _loginfo
_loginfo.ilogRead = ilogRead;
}
break;
case SEEK_CUR:
{
// Advance or retreat from the current read index.
LogIndex ilogRead = _loginfo.ilogRead;
_pcLogFile->AdjustLogIndex( &ilogRead, iSeek, CLogFile::ADJUST_WITHIN_LIMIT,
iSeek >= 0 ? _loginfo.ilogWrite : _loginfo.ilogStart );
SetDirty( TRUE ); // Must be called before changing _loginfo
_loginfo.ilogRead = ilogRead;
}
break;
default:
TrkAssert( FALSE && TEXT("Unexpected origin in CLog::Seek") );
break;
}
// Calculate the sequence number of the entry at the read pointer, and
// use it to store the seq number of the last-read entry (recall that
// the read pointer points to the next entry to be read, not the
// last entry read).
if( IsRead() )
{
seqReadNew = _loginfo.seqNext;
}
else
{
_pcLogFile->ReadMoveNotification( _loginfo.ilogRead, &lmn );
seqReadNew = lmn.seq;
}
SetDirty( TRUE ); // Must be called before changing _loginfo
_loginfo.seqLastRead = seqReadNew - 1;
// Update the entry headers with the new read pointer.
WriteEntryHeader();
// If we've backed up the read pointer, notify the registered callback.
if ( seqReadOriginal > seqReadNew )
{
// Note: This must be the last operation of this method.
_pLogCallback->OnEntriesAvailable();
}
// ----
// Exit
// ----
Exit:
return;
} // CLog::Seek( origin ...
//+----------------------------------------------------------------------------
//
// Method: CLog::IsRead( LogIndex ) (private)
//
// Synopsis: Determine if the specified entry has been read. See also
// the IsRead(void) overload, which checks to see if the whole
// log has been read.
//
// Inputs: [ilog] (in)
// The index in the log to be checked. It is assumed
// that this index points to a valid move notification
// entry.
//
// Outputs: [BOOL]
// True if and only if the entry has been marked as read.
//
//+----------------------------------------------------------------------------
BOOL
CLog::IsRead( LogIndex ilog )
{
LogMoveNotification lmn;
// Has the whole log been read?
if( IsRead() )
return( TRUE );
// Or, has this entry been read?
_pcLogFile->ReadMoveNotification( ilog, &lmn );
if( _loginfo.seqLastRead >= lmn.seq )
return( TRUE );
// Otherwise, we know the entry hasn't been read.
else
return( FALSE );
} // CLog::IsRead( LogIndex )
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