void *zOut, 
  int iAmt, 
  sqlite3_int64 iOffset
){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  sqlite3_int64 filesize;
  int nRead;
  sqlite3_file *pBase = p->pBaseRead;


  /* Grab the write queue mutex for the duration of the call */
  async_mutex_enter(ASYNC_MUTEX_QUEUE);

  /* If an I/O error has previously occurred in this virtual file 
  ** system, then all subsequent operations fail.
  */
  if( async.ioError!=SQLITE_OK ){
    rc = async.ioError;
    goto asyncread_out;
  }

  if( pBase->pMethods ){

    rc = pBase->pMethods->xFileSize(pBase, &filesize);
    if( rc!=SQLITE_OK ){
      goto asyncread_out;
    }
    nRead = (int)MIN(filesize - iOffset, iAmt);
    if( nRead>0 ){
      rc = pBase->pMethods->xRead(pBase, zOut, nRead, iOffset);
      ASYNC_TRACE(("READ %s %d bytes at %d\n", p->zName, nRead, iOffset));
    }
  }

  if( rc==SQLITE_OK ){
................................................................................
    char *zName = p->zName;

    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
      if( pWrite->op==ASYNC_WRITE && (
        (pWrite->pFileData==p) ||
        (zName && pWrite->pFileData->zName==zName)
      )){








        sqlite3_int64 iBeginOut = (pWrite->iOffset-iOffset);
        sqlite3_int64 iBeginIn = -iBeginOut;
        int nCopy;

        if( iBeginIn<0 ) iBeginIn = 0;
        if( iBeginOut<0 ) iBeginOut = 0;
        nCopy = (int)MIN(pWrite->nByte-iBeginIn, iAmt-iBeginOut);


        if( nCopy>0 ){
          memcpy(&((char *)zOut)[iBeginOut], &pWrite->zBuf[iBeginIn], nCopy);
          ASYNC_TRACE(("OVERREAD %d bytes at %d\n", nCopy, iBeginOut+iOffset));
        }
      }
    }
  }

  void *zOut, 
  int iAmt, 
  sqlite3_int64 iOffset
){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  sqlite3_int64 filesize;

  sqlite3_file *pBase = p->pBaseRead;
  sqlite3_int64 iAmt64 = (sqlite3_int64)iAmt;

  /* Grab the write queue mutex for the duration of the call */
  async_mutex_enter(ASYNC_MUTEX_QUEUE);

  /* If an I/O error has previously occurred in this virtual file 
  ** system, then all subsequent operations fail.
  */
  if( async.ioError!=SQLITE_OK ){
    rc = async.ioError;
    goto asyncread_out;
  }

  if( pBase->pMethods ){
    sqlite3_int64 nRead;
    rc = pBase->pMethods->xFileSize(pBase, &filesize);
    if( rc!=SQLITE_OK ){
      goto asyncread_out;
    }
    nRead = MIN(filesize - iOffset, iAmt64);
    if( nRead>0 ){
      rc = pBase->pMethods->xRead(pBase, zOut, nRead, iOffset);
      ASYNC_TRACE(("READ %s %d bytes at %d\n", p->zName, nRead, iOffset));
    }
  }

  if( rc==SQLITE_OK ){
................................................................................
    char *zName = p->zName;

    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
      if( pWrite->op==ASYNC_WRITE && (
        (pWrite->pFileData==p) ||
        (zName && pWrite->pFileData->zName==zName)
      )){
        sqlite3_int64 nCopy;
        sqlite3_int64 nByte64 = (sqlite3_int64)pWrite->nByte;

        /* Set variable iBeginIn to the offset in buffer pWrite->zBuf[] from
        ** which data should be copied. Set iBeginOut to the offset within
        ** the output buffer to which data should be copied. If either of
        ** these offsets is a negative number, set them to 0.
        */
        sqlite3_int64 iBeginOut = (pWrite->iOffset-iOffset);
        sqlite3_int64 iBeginIn = -iBeginOut;


        if( iBeginIn<0 ) iBeginIn = 0;
        if( iBeginOut<0 ) iBeginOut = 0;


        nCopy = MIN(nByte64-iBeginIn, iAmt64-iBeginOut);
        if( nCopy>0 ){
          memcpy(&((char *)zOut)[iBeginOut], &pWrite->zBuf[iBeginIn], nCopy);
          ASYNC_TRACE(("OVERREAD %d bytes at %d\n", nCopy, iBeginOut+iOffset));
        }
      }
    }
  }

# 2009 October 19
#
# 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.
#

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

if {[info commands sqlite3async_initialize] eq ""} {
  # The async logic is not built into this system
  finish_test
  return
}

# Create a database.
do_test tkt-94c94-1.1 {
  execsql { CREATE TABLE t1(a, b) }
} {}

# Grow the file to larger than 4096MB (2^32 bytes)
db close
if {[catch {fake_big_file 4096 [pwd]/test.db} msg]} {
  puts "**** Unable to create a file larger than 4096 MB. *****"
  finish_test
  return
}

# Switch to async mode.
sqlite3async_initialize "" 1
sqlite3 db test.db
sqlite3 db2 test.db

# Read from and write to the db just past the 4096MB mark.
#
do_test tkt-94c94-2.1 {
  execsql { CREATE TABLE t2(x, y) } db
} {}
do_test tkt-94c94-2.2 {
breakpoint
  execsql { INSERT INTO t2 VALUES(1, 2) } db2
} {}
do_test tkt-94c94-2.3 {
  execsql { SELECT * FROM t2 } db
} {1 2}
do_test tkt-94c94-2.4 {
  sqlite3async_control halt idle
  sqlite3async_start
  sqlite3async_wait
} {}
do_test tkt-94c94-2.5 {
  execsql { SELECT * FROM t2 } db
} {1 2}
do_test tkt-94c94-2.6 {
  sqlite3async_start
  sqlite3async_wait
} {}

db close
db2 close
sqlite3async_start
sqlite3async_wait
sqlite3async_shutdown

finish_test