stasis-aries-wal/src/lladd/logger/logHandle.c

/*---
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FOR DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
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POSSIBILITY OF SUCH DAMAGE.

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INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, AND
NON-INFRINGEMENT. THIS SOFTWARE IS PROVIDED ON AN "AS IS" BASIS, AND
THE AUTHORS AND DISTRIBUTORS HAVE NO OBLIGATION TO PROVIDE
MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.

GOVERNMENT USE: If you are acquiring this software on behalf of the
U.S. government, the Government shall have only "Restricted Rights" in
the software and related documentation as defined in the Federal
Acquisition Regulations (FARs) in Clause 52.227.19 (c) (2). If you are
acquiring the software on behalf of the Department of Defense, the
software shall be classified as "Commercial Computer Software" and the
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terms specified in this license.
---*/

#include <lladd/logger/logHandle.h>
#include <lladd/logger/logWriter.h>
#include <config.h> 
#include <malloc.h>

/**
   Sets the next and prev field of h, but does not set h.file_offset.
   That should probably be set before calling this function.
*/

static void set_offsets(LogHandle * h, LogEntry * e, lsn_t lastRead);

/*-------------------------------------------------------*/

LogHandle getLogHandle() {

  lsn_t lsn = firstLogEntry();

  return getGuardedHandle(lsn, NULL, NULL);
}

LogHandle getLSNHandle(lsn_t lsn) {
  return getGuardedHandle(lsn, NULL, NULL);
}

LogHandle getGuardedHandle(lsn_t lsn, guard_fcn_t * guard, void * guard_state) {
  LogHandle ret;
  ret.next_offset = lsn;
  ret.prev_offset = lsn;
  ret.guard = guard;
  ret.guard_state = guard_state;
  return ret;
}

LogEntry * nextInLog(LogHandle * h) {
  LogEntry * ret = readLSNEntry(h->next_offset);
  if(ret != NULL) {
    set_offsets(h, ret, h->next_offset);
  }

  if(h->guard) {
    if(!(h->guard(ret, h->guard_state))) {
      free(ret);
      ret = NULL;
    }
  }


  return ret;
}

LogEntry * previousInTransaction(LogHandle * h) {
  LogEntry * ret = NULL;
  if(h->prev_offset > 0) {
    /* printf("A");  fflush(NULL); */
    ret = readLSNEntry(h->prev_offset);
    set_offsets(h, ret, h->prev_offset);
    /*printf("B");  fflush(NULL); */

    if(h->guard) {
      /*printf("C");  fflush(NULL);*/

      if(!h->guard(ret, h->guard_state)) {
	free(ret);
	ret = NULL;
      }
      /*printf("D");  fflush(NULL);*/

    }
  }

  return ret;

}

/**
   @todo The next_offset field is set in a way that assumes a
   particular layout of log entries.  If we want to support other
   loggers, then the lsn of the next entry should be calculated by the
   logging implementation, not here.  (One possibility is to have
   readLSNEntry return it explicitly.)
*/
static void set_offsets(LogHandle * h, LogEntry * e, lsn_t lastRead) {
  h->next_offset = lastRead + sizeofLogEntry(e)+sizeof(lsn_t);
  h->prev_offset = (e->type==CLRLOG) ? e->contents.clr.undoNextLSN : e->prevLSN ;
}