SQLite

**
** The caller must ensure that the cursor is valid (has eState==CURSOR_VALID)
** prior to calling this routine.  
*/
static int saveCursorPosition(BtCursor *pCur){
  int rc;

  assert( CURSOR_VALID==pCur->eState || CURSOR_SKIPNEXT==pCur->eState );
  assert( 0==pCur->pKey );
  assert( cursorHoldsMutex(pCur) );

  if( pCur->eState==CURSOR_SKIPNEXT ){
    pCur->eState = CURSOR_VALID;
  }else{
    pCur->skipNext = 0;
  }
  rc = sqlite3BtreeKeySize(pCur, &pCur->nKey);
  assert( rc==SQLITE_OK );  /* KeySize() cannot fail */

  /* If this is an intKey table, then the above call to BtreeKeySize()
  ** stores the integer key in pCur->nKey. In this case this value is
  ** all that is required. Otherwise, if pCur is not open on an intKey
  ** table, then malloc space for and store the pCur->nKey bytes of key 

static int SQLITE_NOINLINE saveCursorsOnList(
  BtCursor *p,         /* The first cursor that needs saving */
  Pgno iRoot,          /* Only save cursor with this iRoot. Save all if zero */
  BtCursor *pExcept    /* Do not save this cursor */
){
  do{
    if( p!=pExcept && (0==iRoot || p->pgnoRoot==iRoot) ){
      if( p->eState==CURSOR_VALID || p->eState==CURSOR_SKIPNEXT ){
        int rc = saveCursorPosition(p);
        if( SQLITE_OK!=rc ){
          return rc;
        }
      }else{
        testcase( p->iPage>0 );
        btreeReleaseAllCursorPages(p);

** when saveCursorPosition() was called. Note that this call deletes the 
** saved position info stored by saveCursorPosition(), so there can be
** at most one effective restoreCursorPosition() call after each 
** saveCursorPosition().
*/
static int btreeRestoreCursorPosition(BtCursor *pCur){
  int rc;
  int skipNext;
  assert( cursorHoldsMutex(pCur) );
  assert( pCur->eState>=CURSOR_REQUIRESEEK );
  if( pCur->eState==CURSOR_FAULT ){
    return pCur->skipNext;
  }
  pCur->eState = CURSOR_INVALID;
  rc = btreeMoveto(pCur, pCur->pKey, pCur->nKey, 0, &skipNext);
  if( rc==SQLITE_OK ){
    sqlite3_free(pCur->pKey);
    pCur->pKey = 0;
    assert( pCur->eState==CURSOR_VALID || pCur->eState==CURSOR_INVALID );
    pCur->skipNext |= skipNext;
    if( pCur->skipNext && pCur->eState==CURSOR_VALID ){
      pCur->eState = CURSOR_SKIPNEXT;
    }
  }
  return rc;
}

  assert( pCur!=0 );
  assert( pCur->eState!=CURSOR_VALID );
  rc = restoreCursorPosition(pCur);
  if( rc ){
    *pDifferentRow = 1;
    return rc;
  }
  if( pCur->eState!=CURSOR_VALID || pCur->skipNext!=0 ){
    *pDifferentRow = 1;
  }else{
    *pDifferentRow = 0;
  }
  return SQLITE_OK;
}

  assert( (writeOnly==0 || writeOnly==1) && BTCF_WriteFlag==1 );
  if( pBtree ){
    sqlite3BtreeEnter(pBtree);
    for(p=pBtree->pBt->pCursor; p; p=p->pNext){
      int i;
      if( writeOnly && (p->curFlags & BTCF_WriteFlag)==0 ){
        if( p->eState==CURSOR_VALID || p->eState==CURSOR_SKIPNEXT ){
          rc = saveCursorPosition(p);
          if( rc!=SQLITE_OK ){
            (void)sqlite3BtreeTripAllCursors(pBtree, rc, 0);
            break;
          }
        }
      }else{

# 2015-03-25
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
#
# The focus of this script is making multiple calls to saveCursorPosition()
# and restoreCursorPosition() when cursors have eState==CURSOR_SKIPNEXT
# 

set testdir [file dirname $argv0]
source $testdir/tester.tcl

load_static_extension db eval
do_execsql_test btree02-100 {
  CREATE TABLE t1(a TEXT, ax INTEGER, b INT, PRIMARY KEY(a,ax)) WITHOUT ROWID;
  WITH RECURSIVE c(i) AS (VALUES(1) UNION ALL SELECT i+1 FROM c WHERE i<10)
    INSERT INTO t1(a,ax,b) SELECT printf('%02x',i), random(), i FROM c;
  CREATE INDEX t1a ON t1(a);
  CREATE TABLE t2(x,y);
  CREATE TABLE t3(cnt);
  WITH RECURSIVE c(i) AS (VALUES(1) UNION ALL SELECT i+1 FROM c WHERE i<4)
    INSERT INTO t3(cnt) SELECT i FROM c;
  SELECT count(*) FROM t1;
} {10}
do_test btree02-110 {
  db eval BEGIN
  set i 0
  db eval {SELECT a, ax, b, cnt FROM t1 CROSS JOIN t3 WHERE b IS NOT NULL} {
    db eval {INSERT INTO t2(x,y) VALUES($b,$cnt)}
    # puts "a,b,cnt = ($a,$b,$cnt)"
    incr i
    if {$i%2==1} {
      set bx [expr {$b+1000}]
      # puts "INSERT ($a),$bx"
      db eval {INSERT INTO t1(a,ax,b) VALUES(printf('(%s)',$a),random(),$bx)}
    } else {
      # puts "DELETE a=$a"
      db eval {DELETE FROM t1 WHERE a=$a}
    }
    db eval {COMMIT; BEGIN}
  }  
  db one {COMMIT; SELECT count(*) FROM t1;}
} {20}

finish_test