stasis-aries-wal/stasis/logger/logHandle.h

/*---
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---*/

#include <stasis/logger/logger2.h>

#ifndef __LOGHANDLE_H
#define __LOGHANDLE_H

BEGIN_C_DECLS

/**
   @file 
   A simple data structure that allows forward iterations over
   the log, and also allows reverse iterations.  Forward iterations
   are used for redo, and return every log entry, in its original
   order.  Reverse iterations are used for undo, and are transaction
   specific.  They follow the prevLSN. (or the next entry to be
   undone stored in any CLR's that are encountered.)

   logHandle is useful for read only access to the log.

   @see logWriter.h For write access to the log.
   @see logger2.h for the typedef of the logHandle struct

   $Id$
*/

/** Returns a logHandle pointing at the first log entry in the log.  */
LogHandle getLogHandle();
/** Returns a logHandle pointing at lsn. */
LogHandle getLSNHandle(lsn_t lsn);
/** Returns a 'guarded log handle'.  This handle executes a callback
    function on each entry it encounters.  If the guard returns 0,
    then it's iterator terminates.  Otherwise, it behaves normally. */
LogHandle getGuardedHandle(lsn_t lsn, guard_fcn_t * f, void * guard_state);

/** 
    @return a pointer to the next log entry in the log, or NULL if at
    EOF.

 */
const LogEntry * nextInLog(LogHandle * h);
/** 
    Returns a pointer to the previous log entry in this
    transaction. This is used to undo transactions.  If the logHandle
    is a guarded handle, the handle returns null.  

    The guard is useful for Tprepare, partial rollback, and probably
    any reasonable lock manager implementations.

    If we encounter a CLR, that means that everything after the clr's
    undoNextLSN has already been undone.  In that case, we can skip
    all intervening log entries (including CLR's), since they contain
    'stale' data.  

    @return NULL if there is no previous LogEntry for this
    transaction, or if the guard indicates that we're done by returning 0.
 */
const LogEntry * previousInTransaction(LogHandle * h);
/*
void closeHandle(LogHandle h);
*/
END_C_DECLS

#endif