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/*
* Copyright 2004-2005 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
//----------------------------------------------------------------------------
//
// Module: LogCursor.java
//
// Description: Log file browsing operations.
//
// Product: com.sun.jts.CosTransactions
//
// Author: Simon Holdsworth
//
// Date: March, 1997
//
// Copyright (c): 1995-1997 IBM Corp.
//
// The source code for this program is not published or otherwise divested
// of its trade secrets, irrespective of what has been deposited with the
// U.S. Copyright Office.
//
// This software contains confidential and proprietary information of
// IBM Corp.
//----------------------------------------------------------------------------
package com.sun.jts.CosTransactions;
// Import required classes.
import java.util.*;
/**Contains information for an open cursor.
*
* @version 0.01
*
* @author Simon Holdsworth, IBM Corporation
*
* @see
*/
//----------------------------------------------------------------------------
// CHANGE HISTORY
//
// Version By Change Description
// 0.01 SAJH Initial implementation.
//-----------------------------------------------------------------------------
class LogCursor {
/**Constants used to identify browse direction.
*/
final static int ASCENDING = 0;
final static int DESCENDING = 1;
/**Internal instance members.
*/
LogCursor blockValid;
LogControl logControl;
LogHandle logHandle;
LogLSN startLSN;
LogLSN endLSN;
LogLSN currentLSN;
int direction;
boolean symbolicsChecked;
/**Creates a cursor for a browse in the given range.
*
* @param control The LogControl object for the log instance.
* @param handle the handle for the log file.
* @param startLSN The LSN for the start of the browse.
* @param endLSN The LSN for the end of the browse.
*
* @return
*
* @see
*/
LogCursor( LogControl control,
LogHandle handle,
LogLSN startLSN,
LogLSN endLSN ) {
logHandle = handle;
logControl = control;
// Initialise the Log_CursorDescriptor block
// - set start of range field to startLsn
// - set end of range field to endLsn
// - set current position to startLsn
// - IF startLsn < endLsn
// set direction field to ASCENDING
// ELSE
// set direction field to DESCENDING
// - set the file descriptor to the logHandle parameter
// - set the BlockValid field to the address of the
// Log_FileDescriptor block
this.startLSN = new LogLSN(startLSN);
currentLSN = new LogLSN(startLSN);
this.endLSN = new LogLSN(endLSN);
if( startLSN.lessThan(endLSN) )
direction = ASCENDING;
else
direction = DESCENDING;
blockValid = this;
symbolicsChecked = false;
}
/**Destroys a cursor.
*
* @param
*
* @return
*
* @see
*/
/*
public void finalize() {
blockValid = null;
}
*/
/**Reads a record from the cursor.
*
* @param type An array which will contain the type for record read.
* @param LSNread The LSN of the record read.
*
* @return The bytes read.
*
* @exception LogException The operation failed.
*
* @see
*/
synchronized byte[] readCursor( int[/*1*/] type,
LogLSN LSNread )
throws LogException {
// Check BlockValid field in Log_CursorDescriptor block pointed to
// by cursorId parameter, and ensure it is valid
// IF not valid Log_CursorDescriptor
// Return LOG_INVALID_CURSOR
if( blockValid != this )
throw new LogException(null,LogException.LOG_INVALID_CURSOR,1);
// Check BlockValid field in Log_FileDescriptor block pointed to
// by field in Log_CursorDescriptor block and ensure it is valid
if( logHandle == null || logHandle.blockValid != logHandle )
throw new LogException(null,LogException.LOG_INVALID_CURSOR,2);
// IF not LogInitialised Return LOG_NOT_INITIALISED
if( !logControl.logInitialised )
throw new LogException(null,LogException.LOG_NOT_INITIALISED,3);
// IF the head LSN in the Log_FileDescriptor block = LOG_NULL_LSN
// Unlock the Log_FileDescriptor latch
// Return LOG_END_OF_CURSOR
if( logHandle.logControlDescriptor.headLSN.isNULL() )
throw new LogException(null,LogException.LOG_END_OF_CURSOR,5);
// Check if the current position in Log_CursorDescriptor block
// contains symbolic constants
// IF equal to LOG_HEAD_LSN
// Replace it with head LSN value from Log_FileDescriptor block
// ELSE
// IF equal to LOG_TAIL_LSN
// Replace it with tail LSN value from Log_FileDescriptor block
if( !symbolicsChecked ) {
if( currentLSN.equals(LogLSN.HEAD_LSN) )
currentLSN.copy(logHandle.logControlDescriptor.headLSN);
else if( currentLSN.equals(LogLSN.TAIL_LSN) )
currentLSN.copy(logHandle.logControlDescriptor.tailLSN);
symbolicsChecked = true;
}
// Check that the current position lies within the log record range
// IF current position > head LSN (in Log_FileDescriptor block)
// Indicate 'end of cursor'
// ELSE
// IF current position < tail LSN (indicating log truncate)
// Indicate 'end of cursor'
// IF 'end of cursor' has been set
// Unlock the Log_FileDescriptor latch
// Return LOG_END_OF_CURSOR
if( currentLSN.greaterThan(logHandle.logControlDescriptor.headLSN) ||
currentLSN.lessThan(logHandle.logControlDescriptor.tailLSN) )
throw new LogException(null,LogException.LOG_END_OF_CURSOR,6);
// Now retrieve the record identified by the CurrentLogLSN value.
// This is done in a loop, since we may have to do this more than once
// if the 'current position' LSN points to a link record.
boolean recordRetrieved = false;
LogExtent logEDP = null;
LogRecordHeader logRH = null;
LogRecordEnding logRE = null;
while( !recordRetrieved ) {
// Determine the extent file containing the 'current position'
// log record
// Position the file pointer at the 'current position' using LSEEK
// IF not successful allow the error to pass to the caller.
// Unlock the Log_FileDescriptor latch
// Return error from Log_PositionFilePointer function
logEDP = logHandle.positionFilePointer(currentLSN,0,LogExtent.ACCESSTYPE_READ);
// Issue READ to get the log record header
// IF not successful
// set last access as unknown as we cannot be sure of the
// new cursor position.
// Unlock the Log_FileDescriptor latch
// return LOG_READ_FAILURE
byte[] headerBytes = new byte[LogRecordHeader.SIZEOF];
int bytesRead = 0;
try {
bytesRead = logEDP.fileHandle.fileRead(headerBytes);
} catch( LogException le ) {
logEDP.lastAccess = LogExtent.ACCESSTYPE_UNKNOWN;
throw new LogException(null,LogException.LOG_READ_FAILURE,8);
}
logRH = new LogRecordHeader(headerBytes,0);
logEDP.cursorPosition += bytesRead;
// IF the lsn value in the record header is not same as the
// 'current cursor position' lsn
// Unlock the Log_FileDescriptor latch
// Return LOG_CORRUPTED
if( !logRH.currentLSN.equals(currentLSN) )
throw new LogException(null,LogException.LOG_CORRUPTED,9);
// Check the record header in case its a link record thats been read in
// IF it is a link record
// IF cursor is ASCENDING
// Set 'current position' to next LSN in link record
// ELSE
// Set 'current position' to previous LSN in link record
// Iterate LOOP
if( logRH.recordType == LogHandle.LINK )
if( direction == ASCENDING )
currentLSN.copy(logRH.nextLSN);
else
currentLSN.copy(logRH.previousLSN);
else
recordRetrieved = true;
}
// Set up a 2-element iovec array so that the record data
// and record ending are separated during the READV
byte[][] readVect = new byte[2][];
readVect[0] = new byte[logRH.recordLength];
readVect[1] = new byte[LogRecordEnding.SIZEOF];
// Issue READV to get the log record
// IF not successful
// Unlock the Log_FileDescriptor latch
// Return LOG_READ_FAILURE
int bytesRead = 0;
try {
bytesRead = logEDP.fileHandle.readVector(readVect);
} catch( LogException le ) {
logEDP.lastAccess = LogExtent.ACCESSTYPE_UNKNOWN;
throw new LogException(null,le.errorCode,11);
}
logEDP.cursorPosition += bytesRead;
logRE = new LogRecordEnding(readVect[1],0);
// IF the lsn contained in the record ending is not the same as the
// 'current cursor position' lsn
// Unlock the Log_FileDescriptor latch
// Return LOG_CORRUPTED
if( !logRE.currentLSN.equals(currentLSN) )
throw new LogException(null,LogException.LOG_CORRUPTED,12);
// Update the Log_CursorDescriptor 'current position'
// IF cursor is ASCENDING
// Set 'current position' to next LSN in log record
// ELSE
// Set 'current position' to previous LSN in log record
if( direction == ASCENDING )
currentLSN.copy(logRH.nextLSN);
else
currentLSN.copy(logRH.previousLSN);
// Copy the record type and lsn values from the
// Log_RecordHeader to callers recordTypeP and lsnP
// parameters respectively
type[0] = logRH.recordType;
LSNread.copy(logRH.currentLSN);
// Return LOG_SUCCESS
return readVect[0];
}
}
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