SQLite

    if( pCur->pNext ){
      pCur->pNext->pPrev = pCur->pPrev;
    }
    for(i=0; i<=pCur->iPage; i++){
      releasePage(pCur->apPage[i]);
    }
    unlockBtreeIfUnused(pBt);
    sqlite3_free(pCur->aOverflow);
    /* sqlite3_free(pCur); */
    sqlite3BtreeLeave(pBtree);
  }
  return SQLITE_OK;
}

/*

    rc = copyPayload(&aPayload[offset], pBuf, a, (eOp & 0x01), pPage->pDbPage);
    offset = 0;
    pBuf += a;
    amt -= a;
  }else{
    offset -= pCur->info.nLocal;
  }


  if( rc==SQLITE_OK && amt>0 ){
    const u32 ovflSize = pBt->usableSize - 4;  /* Bytes content per ovfl page */
    Pgno nextPage;

    nextPage = get4byte(&aPayload[pCur->info.nLocal]);

    /* If the BtCursor.aOverflow[] has not been allocated, allocate it now.
    ** Except, do not allocate aOverflow[] for eOp==2.
    **
    ** The aOverflow[] array is sized at one entry for each overflow page
    ** in the overflow chain. The page number of the first overflow page is
    ** stored in aOverflow[0], etc. A value of 0 in the aOverflow[] array
    ** means "not yet known" (the cache is lazily populated).
    */
    if( eOp!=2 && (pCur->curFlags & BTCF_ValidOvfl)==0 ){
      int nOvfl = (pCur->info.nPayload-pCur->info.nLocal+ovflSize-1)/ovflSize;
      if( nOvfl>pCur->nOvflAlloc ){
        Pgno *aNew = (Pgno*)sqlite3Realloc(
            pCur->aOverflow, nOvfl*2*sizeof(Pgno)
        );
        if( aNew==0 ){
          rc = SQLITE_NOMEM;
        }else{
          pCur->nOvflAlloc = nOvfl*2;
          pCur->aOverflow = aNew;
        }

        ** function.
        **
        ** Note that the aOverflow[] array must be allocated because eOp!=2
        ** here.  If eOp==2, then offset==0 and this branch is never taken.
        */
        assert( eOp!=2 );
        assert( pCur->curFlags & BTCF_ValidOvfl );
        assert( pCur->pBtree->db==pBt->db );
        if( pCur->aOverflow[iIdx+1] ){
          nextPage = pCur->aOverflow[iIdx+1];
        }else{
          rc = getOverflowPage(pBt, nextPage, 0, &nextPage);
        }
        offset -= ovflSize;
      }else{

    ** into the database handle. This block copies the error message 
    ** from the database handle into the statement and sets the statement
    ** program counter to 0 to ensure that when the statement is 
    ** finalized or reset the parser error message is available via
    ** sqlite3_errmsg() and sqlite3_errcode().
    */
    const char *zErr = (const char *)sqlite3_value_text(db->pErr); 

    sqlite3DbFree(db, v->zErrMsg);
    if( !db->mallocFailed ){
      v->zErrMsg = sqlite3DbStrDup(db, zErr);
      v->rc = rc2;
    } else {
      v->zErrMsg = 0;
      v->rc = rc = SQLITE_NOMEM;

  print_and_free_err(&err);
}



#include "tt3_checkpoint.c"
#include "tt3_index.c"
#include "tt3_lookaside1.c"

int main(int argc, char **argv){
  struct ThreadTest {
    void (*xTest)(int);
    const char *zTest;
    int nMs;
  } aTest[] = {

    { cgt_pager_1,      "cgt_pager_1", 0 },
    { dynamic_triggers, "dynamic_triggers", 20000 },

    { checkpoint_starvation_1, "checkpoint_starvation_1", 10000 },
    { checkpoint_starvation_2, "checkpoint_starvation_2", 10000 },

    { create_drop_index_1, "create_drop_index_1", 10000 },
    { lookaside1, "lookaside1", 10000 },
  };

  int i;
  char *zTest = 0;
  int nTest = 0;
  int bTestfound = 0;
  int bPrefix = 0;

  sqlite3_enable_shared_cache(1);
  launch_thread(&err, &threads, create_drop_index_thread, 0);
  launch_thread(&err, &threads, create_drop_index_thread, 0);
  launch_thread(&err, &threads, create_drop_index_thread, 0);
  launch_thread(&err, &threads, create_drop_index_thread, 0);
  launch_thread(&err, &threads, create_drop_index_thread, 0);


  join_all_threads(&err, &threads);
  sqlite3_enable_shared_cache(0);
  print_and_free_err(&err);
}

/*
** 2014 December 9
**
** 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.
**
*************************************************************************
**
**     lookaside1
*/

/*
** The test in this file attempts to expose a specific race condition
** that is suspected to exist at time of writing.
*/

static char *lookaside1_thread_reader(int iTid, int iArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

  opendb(&err, &db, "test.db", 0);

  while( !timetostop(&err) ){
    sqlite3_stmt *pStmt = 0;
    int rc;

    sqlite3_prepare_v2(db.db, "SELECT 1 FROM t1", -1, &pStmt, 0);
    while( sqlite3_step(pStmt)==SQLITE_ROW ){
      execsql(&err, &db, "SELECT length(x||y||z) FROM t2");
    }
    rc = sqlite3_finalize(pStmt);
    if( err.rc==SQLITE_OK && rc!=SQLITE_OK ){
      sqlite_error(&err, &db, "finalize");
    }
  }

  closedb(&err, &db);
  print_and_free_err(&err);
  return sqlite3_mprintf("ok");
}

static char *lookaside1_thread_writer(int iTid, int iArg){
  Error err = {0};                /* Error code and message */
  Sqlite db = {0};                /* SQLite database connection */

  opendb(&err, &db, "test.db", 0);

  do{
    sql_script(&err, &db, 
      "BEGIN;"
        "UPDATE t3 SET i=i+1 WHERE x=1;"
      "ROLLBACK;"
    );
  }while( !timetostop(&err) );

  closedb(&err, &db);
  print_and_free_err(&err);
  return sqlite3_mprintf("ok");
}


static void lookaside1(int nMs){
  Error err = {0};
  Sqlite db = {0};
  Threadset threads = {0};

  opendb(&err, &db, "test.db", 1);
  sql_script(&err, &db, 
     "CREATE TABLE t1(x PRIMARY KEY) WITHOUT ROWID;"
     "WITH data(x,y) AS ("
     "  SELECT 1, quote(randomblob(750)) UNION ALL "
     "  SELECT x*2, y||y FROM data WHERE x<5) "
     "INSERT INTO t1 SELECT y FROM data;"

     "CREATE TABLE t3(x PRIMARY KEY,i) WITHOUT ROWID;"
     "INSERT INTO t3 VALUES(1, 1);"

     "CREATE TABLE t2(x,y,z);"
     "INSERT INTO t2 VALUES(randomblob(50), randomblob(50), randomblob(50));"
  );
  closedb(&err, &db);

  setstoptime(&err, nMs);

  sqlite3_enable_shared_cache(1);
  launch_thread(&err, &threads, lookaside1_thread_reader, 0);
  launch_thread(&err, &threads, lookaside1_thread_reader, 0);
  launch_thread(&err, &threads, lookaside1_thread_reader, 0);
  launch_thread(&err, &threads, lookaside1_thread_reader, 0);
  launch_thread(&err, &threads, lookaside1_thread_reader, 0);
  launch_thread(&err, &threads, lookaside1_thread_writer, 0);
  join_all_threads(&err, &threads);
  sqlite3_enable_shared_cache(0);
  print_and_free_err(&err);
}