Move bundled copy of sqlite one level deeper to better separate it...

third_party/sqlite/ext/async/sqlite3async.c

Index: third_party/sqlite/ext/async/sqlite3async.c
===================================================================
--- third_party/sqlite/ext/async/sqlite3async.c	(revision 56608)
+++ third_party/sqlite/ext/async/sqlite3async.c	(working copy)
@@ -1,1683 +0,0 @@
-/*
-** 2005 December 14
-**
-** 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.
-**
-*************************************************************************
-**
-** $Id: sqlite3async.c,v 1.7 2009/07/18 11:52:04 danielk1977 Exp $
-**
-** This file contains the implementation of an asynchronous IO backend 
-** for SQLite.
-*/
-
-#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO)
-
-#include "sqlite3async.h"
-#include "sqlite3.h"
-#include <stdarg.h>
-#include <string.h>
-#include <assert.h>
-
-/* Useful macros used in several places */
-#define MIN(x,y) ((x)<(y)?(x):(y))
-#define MAX(x,y) ((x)>(y)?(x):(y))
-
-#ifndef SQLITE_AMALGAMATION
-/* Macro to mark parameters as unused and silence compiler warnings. */
-#define UNUSED_PARAMETER(x) (void)(x)
-#endif
-
-/* Forward references */
-typedef struct AsyncWrite AsyncWrite;
-typedef struct AsyncFile AsyncFile;
-typedef struct AsyncFileData AsyncFileData;
-typedef struct AsyncFileLock AsyncFileLock;
-typedef struct AsyncLock AsyncLock;
-
-/* Enable for debugging */
-#ifndef NDEBUG
-#include <stdio.h>
-static int sqlite3async_trace = 0;
-# define ASYNC_TRACE(X) if( sqlite3async_trace ) asyncTrace X
-static void asyncTrace(const char *zFormat, ...){
-  char *z;
-  va_list ap;
-  va_start(ap, zFormat);
-  z = sqlite3_vmprintf(zFormat, ap);
-  va_end(ap);
-  fprintf(stderr, "[%d] %s", 0 /* (int)pthread_self() */, z);
-  sqlite3_free(z);
-}
-#else
-# define ASYNC_TRACE(X)
-#endif
-
-/*
-** THREAD SAFETY NOTES
-**
-** Basic rules:
-**
-**     * Both read and write access to the global write-op queue must be 
-**       protected by the async.queueMutex. As are the async.ioError and
-**       async.nFile variables.
-**
-**     * The async.pLock list and all AsyncLock and AsyncFileLock
-**       structures must be protected by the async.lockMutex mutex.
-**
-**     * The file handles from the underlying system are not assumed to 
-**       be thread safe.
-**
-**     * See the last two paragraphs under "The Writer Thread" for
-**       an assumption to do with file-handle synchronization by the Os.
-**
-** Deadlock prevention:
-**
-**     There are three mutex used by the system: the "writer" mutex, 
-**     the "queue" mutex and the "lock" mutex. Rules are:
-**
-**     * It is illegal to block on the writer mutex when any other mutex
-**       are held, and 
-**
-**     * It is illegal to block on the queue mutex when the lock mutex
-**       is held.
-**
-**     i.e. mutex's must be grabbed in the order "writer", "queue", "lock".
-**
-** File system operations (invoked by SQLite thread):
-**
-**     xOpen
-**     xDelete
-**     xFileExists
-**
-** File handle operations (invoked by SQLite thread):
-**
-**         asyncWrite, asyncClose, asyncTruncate, asyncSync 
-**    
-**     The operations above add an entry to the global write-op list. They
-**     prepare the entry, acquire the async.queueMutex momentarily while
-**     list pointers are  manipulated to insert the new entry, then release
-**     the mutex and signal the writer thread to wake up in case it happens
-**     to be asleep.
-**
-**    
-**         asyncRead, asyncFileSize.
-**
-**     Read operations. Both of these read from both the underlying file
-**     first then adjust their result based on pending writes in the 
-**     write-op queue.   So async.queueMutex is held for the duration
-**     of these operations to prevent other threads from changing the
-**     queue in mid operation.
-**    
-**
-**         asyncLock, asyncUnlock, asyncCheckReservedLock
-**    
-**     These primitives implement in-process locking using a hash table
-**     on the file name.  Files are locked correctly for connections coming
-**     from the same process.  But other processes cannot see these locks
-**     and will therefore not honor them.
-**
-**
-** The writer thread:
-**
-**     The async.writerMutex is used to make sure only there is only
-**     a single writer thread running at a time.
-**
-**     Inside the writer thread is a loop that works like this:
-**
-**         WHILE (write-op list is not empty)
-**             Do IO operation at head of write-op list
-**             Remove entry from head of write-op list
-**         END WHILE
-**
-**     The async.queueMutex is always held during the <write-op list is 
-**     not empty> test, and when the entry is removed from the head
-**     of the write-op list. Sometimes it is held for the interim
-**     period (while the IO is performed), and sometimes it is
-**     relinquished. It is relinquished if (a) the IO op is an
-**     ASYNC_CLOSE or (b) when the file handle was opened, two of
-**     the underlying systems handles were opened on the same
-**     file-system entry.
-**
-**     If condition (b) above is true, then one file-handle 
-**     (AsyncFile.pBaseRead) is used exclusively by sqlite threads to read the
-**     file, the other (AsyncFile.pBaseWrite) by sqlite3_async_flush() 
-**     threads to perform write() operations. This means that read 
-**     operations are not blocked by asynchronous writes (although 
-**     asynchronous writes may still be blocked by reads).
-**
-**     This assumes that the OS keeps two handles open on the same file
-**     properly in sync. That is, any read operation that starts after a
-**     write operation on the same file system entry has completed returns
-**     data consistent with the write. We also assume that if one thread 
-**     reads a file while another is writing it all bytes other than the
-**     ones actually being written contain valid data.
-**
-**     If the above assumptions are not true, set the preprocessor symbol
-**     SQLITE_ASYNC_TWO_FILEHANDLES to 0.
-*/
-
-
-#ifndef NDEBUG
-# define TESTONLY( X ) X
-#else
-# define TESTONLY( X )
-#endif
-
-/*
-** PORTING FUNCTIONS
-**
-** There are two definitions of the following functions. One for pthreads
-** compatible systems and one for Win32. These functions isolate the OS
-** specific code required by each platform.
-**
-** The system uses three mutexes and a single condition variable. To
-** block on a mutex, async_mutex_enter() is called. The parameter passed
-** to async_mutex_enter(), which must be one of ASYNC_MUTEX_LOCK,
-** ASYNC_MUTEX_QUEUE or ASYNC_MUTEX_WRITER, identifies which of the three
-** mutexes to lock. Similarly, to unlock a mutex, async_mutex_leave() is
-** called with a parameter identifying the mutex being unlocked. Mutexes
-** are not recursive - it is an error to call async_mutex_enter() to
-** lock a mutex that is already locked, or to call async_mutex_leave()
-** to unlock a mutex that is not currently locked.
-**
-** The async_cond_wait() and async_cond_signal() functions are modelled
-** on the pthreads functions with similar names. The first parameter to
-** both functions is always ASYNC_COND_QUEUE. When async_cond_wait()
-** is called the mutex identified by the second parameter must be held.
-** The mutex is unlocked, and the calling thread simultaneously begins 
-** waiting for the condition variable to be signalled by another thread.
-** After another thread signals the condition variable, the calling
-** thread stops waiting, locks mutex eMutex and returns. The 
-** async_cond_signal() function is used to signal the condition variable. 
-** It is assumed that the mutex used by the thread calling async_cond_wait() 
-** is held by the caller of async_cond_signal() (otherwise there would be 
-** a race condition).
-**
-** It is guaranteed that no other thread will call async_cond_wait() when
-** there is already a thread waiting on the condition variable.
-**
-** The async_sched_yield() function is called to suggest to the operating
-** system that it would be a good time to shift the current thread off the
-** CPU. The system will still work if this function is not implemented
-** (it is not currently implemented for win32), but it might be marginally
-** more efficient if it is.
-*/
-static void async_mutex_enter(int eMutex);
-static void async_mutex_leave(int eMutex);
-static void async_cond_wait(int eCond, int eMutex);
-static void async_cond_signal(int eCond);
-static void async_sched_yield(void);
-
-/*
-** There are also two definitions of the following. async_os_initialize()
-** is called when the asynchronous VFS is first installed, and os_shutdown()
-** is called when it is uninstalled (from within sqlite3async_shutdown()).
-**
-** For pthreads builds, both of these functions are no-ops. For win32,
-** they provide an opportunity to initialize and finalize the required
-** mutex and condition variables.
-**
-** If async_os_initialize() returns other than zero, then the initialization
-** fails and SQLITE_ERROR is returned to the user.
-*/
-static int async_os_initialize(void);
-static void async_os_shutdown(void);
-
-/* Values for use as the 'eMutex' argument of the above functions. The
-** integer values assigned to these constants are important for assert()
-** statements that verify that mutexes are locked in the correct order.
-** Specifically, it is unsafe to try to lock mutex N while holding a lock 
-** on mutex M if (M<=N).
-*/
-#define ASYNC_MUTEX_LOCK    0
-#define ASYNC_MUTEX_QUEUE   1
-#define ASYNC_MUTEX_WRITER  2
-
-/* Values for use as the 'eCond' argument of the above functions. */
-#define ASYNC_COND_QUEUE    0
-
-/*************************************************************************
-** Start of OS specific code.
-*/
-#if SQLITE_OS_WIN || defined(_WIN32) || defined(WIN32) || defined(__CYGWIN__) || defined(__MINGW32__) || defined(__BORLANDC__)
-
-#include <windows.h>
-
-/* The following block contains the win32 specific code. */
-
-#define mutex_held(X) (GetCurrentThreadId()==primitives.aHolder[X])
-
-static struct AsyncPrimitives {
-  int isInit;
-  DWORD aHolder[3];
-  CRITICAL_SECTION aMutex[3];
-  HANDLE aCond[1];
-} primitives = { 0 };
-
-static int async_os_initialize(void){
-  if( !primitives.isInit ){
-    primitives.aCond[0] = CreateEvent(NULL, TRUE, FALSE, 0);
-    if( primitives.aCond[0]==NULL ){
-      return 1;
-    }
-    InitializeCriticalSection(&primitives.aMutex[0]);
-    InitializeCriticalSection(&primitives.aMutex[1]);
-    InitializeCriticalSection(&primitives.aMutex[2]);
-    primitives.isInit = 1;
-  }
-  return 0;
-}
-static void async_os_shutdown(void){
-  if( primitives.isInit ){
-    DeleteCriticalSection(&primitives.aMutex[0]);
-    DeleteCriticalSection(&primitives.aMutex[1]);
-    DeleteCriticalSection(&primitives.aMutex[2]);
-    CloseHandle(primitives.aCond[0]);
-    primitives.isInit = 0;
-  }
-}
-
-/* The following block contains the Win32 specific code. */
-static void async_mutex_enter(int eMutex){
-  assert( eMutex==0 || eMutex==1 || eMutex==2 );
-  assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
-  assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
-  assert( eMutex!=0 || (!mutex_held(0)) );
-  EnterCriticalSection(&primitives.aMutex[eMutex]);
-  TESTONLY( primitives.aHolder[eMutex] = GetCurrentThreadId(); )
-}
-static void async_mutex_leave(int eMutex){
-  assert( eMutex==0 || eMutex==1 || eMutex==2 );
-  assert( mutex_held(eMutex) );
-  TESTONLY( primitives.aHolder[eMutex] = 0; )
-  LeaveCriticalSection(&primitives.aMutex[eMutex]);
-}
-static void async_cond_wait(int eCond, int eMutex){
-  ResetEvent(primitives.aCond[eCond]);
-  async_mutex_leave(eMutex);
-  WaitForSingleObject(primitives.aCond[eCond], INFINITE);
-  async_mutex_enter(eMutex);
-}
-static void async_cond_signal(int eCond){
-  assert( mutex_held(ASYNC_MUTEX_QUEUE) );
-  SetEvent(primitives.aCond[eCond]);
-}
-static void async_sched_yield(void){
-  Sleep(0);
-}
-#else
-
-/* The following block contains the pthreads specific code. */
-#include <pthread.h>
-#include <sched.h>
-
-#define mutex_held(X) pthread_equal(primitives.aHolder[X], pthread_self())
-
-static int  async_os_initialize(void) {return 0;}
-static void async_os_shutdown(void) {}
-
-static struct AsyncPrimitives {
-  pthread_mutex_t aMutex[3];
-  pthread_cond_t aCond[1];
-  pthread_t aHolder[3];
-} primitives = {
-  { PTHREAD_MUTEX_INITIALIZER, 
-    PTHREAD_MUTEX_INITIALIZER, 
-    PTHREAD_MUTEX_INITIALIZER
-  } , {
-    PTHREAD_COND_INITIALIZER
-  } , { 0, 0, 0 }
-};
-
-static void async_mutex_enter(int eMutex){
-  assert( eMutex==0 || eMutex==1 || eMutex==2 );
-  assert( eMutex!=2 || (!mutex_held(0) && !mutex_held(1) && !mutex_held(2)) );
-  assert( eMutex!=1 || (!mutex_held(0) && !mutex_held(1)) );
-  assert( eMutex!=0 || (!mutex_held(0)) );
-  pthread_mutex_lock(&primitives.aMutex[eMutex]);
-  TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
-}
-static void async_mutex_leave(int eMutex){
-  assert( eMutex==0 || eMutex==1 || eMutex==2 );
-  assert( mutex_held(eMutex) );
-  TESTONLY( primitives.aHolder[eMutex] = 0; )
-  pthread_mutex_unlock(&primitives.aMutex[eMutex]);
-}
-static void async_cond_wait(int eCond, int eMutex){
-  assert( eMutex==0 || eMutex==1 || eMutex==2 );
-  assert( mutex_held(eMutex) );
-  TESTONLY( primitives.aHolder[eMutex] = 0; )
-  pthread_cond_wait(&primitives.aCond[eCond], &primitives.aMutex[eMutex]);
-  TESTONLY( primitives.aHolder[eMutex] = pthread_self(); )
-}
-static void async_cond_signal(int eCond){
-  assert( mutex_held(ASYNC_MUTEX_QUEUE) );
-  pthread_cond_signal(&primitives.aCond[eCond]);
-}
-static void async_sched_yield(void){
-  sched_yield();
-}
-#endif
-/*
-** End of OS specific code.
-*************************************************************************/
-
-#define assert_mutex_is_held(X) assert( mutex_held(X) )
-
-
-#ifndef SQLITE_ASYNC_TWO_FILEHANDLES
-/* #define SQLITE_ASYNC_TWO_FILEHANDLES 0 */
-#define SQLITE_ASYNC_TWO_FILEHANDLES 1
-#endif
-
-/*
-** State information is held in the static variable "async" defined
-** as the following structure.
-**
-** Both async.ioError and async.nFile are protected by async.queueMutex.
-*/
-static struct TestAsyncStaticData {
-  AsyncWrite *pQueueFirst;     /* Next write operation to be processed */
-  AsyncWrite *pQueueLast;      /* Last write operation on the list */
-  AsyncLock *pLock;            /* Linked list of all AsyncLock structures */
-  volatile int ioDelay;        /* Extra delay between write operations */
-  volatile int eHalt;          /* One of the SQLITEASYNC_HALT_XXX values */
-  volatile int bLockFiles;     /* Current value of "lockfiles" parameter */
-  int ioError;                 /* True if an IO error has occurred */
-  int nFile;                   /* Number of open files (from sqlite pov) */
-} async = { 0,0,0,0,0,1,0,0 };
-
-/* Possible values of AsyncWrite.op */
-#define ASYNC_NOOP          0
-#define ASYNC_WRITE         1
-#define ASYNC_SYNC          2
-#define ASYNC_TRUNCATE      3
-#define ASYNC_CLOSE         4
-#define ASYNC_DELETE        5
-#define ASYNC_OPENEXCLUSIVE 6
-#define ASYNC_UNLOCK        7
-
-/* Names of opcodes.  Used for debugging only.
-** Make sure these stay in sync with the macros above!
-*/
-static const char *azOpcodeName[] = {
-  "NOOP", "WRITE", "SYNC", "TRUNCATE", "CLOSE", "DELETE", "OPENEX", "UNLOCK"
-};
-
-/*
-** Entries on the write-op queue are instances of the AsyncWrite
-** structure, defined here.
-**
-** The interpretation of the iOffset and nByte variables varies depending 
-** on the value of AsyncWrite.op:
-**
-** ASYNC_NOOP:
-**     No values used.
-**
-** ASYNC_WRITE:
-**     iOffset -> Offset in file to write to.
-**     nByte   -> Number of bytes of data to write (pointed to by zBuf).
-**
-** ASYNC_SYNC:
-**     nByte   -> flags to pass to sqlite3OsSync().
-**
-** ASYNC_TRUNCATE:
-**     iOffset -> Size to truncate file to.
-**     nByte   -> Unused.
-**
-** ASYNC_CLOSE:
-**     iOffset -> Unused.
-**     nByte   -> Unused.
-**
-** ASYNC_DELETE:
-**     iOffset -> Contains the "syncDir" flag.
-**     nByte   -> Number of bytes of zBuf points to (file name).
-**
-** ASYNC_OPENEXCLUSIVE:
-**     iOffset -> Value of "delflag".
-**     nByte   -> Number of bytes of zBuf points to (file name).
-**
-** ASYNC_UNLOCK:
-**     nByte   -> Argument to sqlite3OsUnlock().
-**
-**
-** For an ASYNC_WRITE operation, zBuf points to the data to write to the file. 
-** This space is sqlite3_malloc()d along with the AsyncWrite structure in a
-** single blob, so is deleted when sqlite3_free() is called on the parent 
-** structure.
-*/
-struct AsyncWrite {
-  AsyncFileData *pFileData;    /* File to write data to or sync */
-  int op;                      /* One of ASYNC_xxx etc. */
-  sqlite_int64 iOffset;        /* See above */
-  int nByte;          /* See above */
-  char *zBuf;         /* Data to write to file (or NULL if op!=ASYNC_WRITE) */
-  AsyncWrite *pNext;  /* Next write operation (to any file) */
-};
-
-/*
-** An instance of this structure is created for each distinct open file 
-** (i.e. if two handles are opened on the one file, only one of these
-** structures is allocated) and stored in the async.aLock hash table. The
-** keys for async.aLock are the full pathnames of the opened files.
-**
-** AsyncLock.pList points to the head of a linked list of AsyncFileLock
-** structures, one for each handle currently open on the file.
-**
-** If the opened file is not a main-database (the SQLITE_OPEN_MAIN_DB is
-** not passed to the sqlite3OsOpen() call), or if async.bLockFiles is 
-** false, variables AsyncLock.pFile and AsyncLock.eLock are never used. 
-** Otherwise, pFile is a file handle opened on the file in question and 
-** used to obtain the file-system locks required by database connections 
-** within this process.
-**
-** See comments above the asyncLock() function for more details on 
-** the implementation of database locking used by this backend.
-*/
-struct AsyncLock {
-  char *zFile;
-  int nFile;
-  sqlite3_file *pFile;
-  int eLock;
-  AsyncFileLock *pList;
-  AsyncLock *pNext;           /* Next in linked list headed by async.pLock */
-};
-
-/*
-** An instance of the following structure is allocated along with each
-** AsyncFileData structure (see AsyncFileData.lock), but is only used if the
-** file was opened with the SQLITE_OPEN_MAIN_DB.
-*/
-struct AsyncFileLock {
-  int eLock;                /* Internally visible lock state (sqlite pov) */
-  int eAsyncLock;           /* Lock-state with write-queue unlock */
-  AsyncFileLock *pNext;
-};
-
-/* 
-** The AsyncFile structure is a subclass of sqlite3_file used for 
-** asynchronous IO. 
-**
-** All of the actual data for the structure is stored in the structure
-** pointed to by AsyncFile.pData, which is allocated as part of the
-** sqlite3OsOpen() using sqlite3_malloc(). The reason for this is that the
-** lifetime of the AsyncFile structure is ended by the caller after OsClose()
-** is called, but the data in AsyncFileData may be required by the
-** writer thread after that point.
-*/
-struct AsyncFile {
-  sqlite3_io_methods *pMethod;
-  AsyncFileData *pData;
-};
-struct AsyncFileData {
-  char *zName;               /* Underlying OS filename - used for debugging */
-  int nName;                 /* Number of characters in zName */
-  sqlite3_file *pBaseRead;   /* Read handle to the underlying Os file */
-  sqlite3_file *pBaseWrite;  /* Write handle to the underlying Os file */
-  AsyncFileLock lock;        /* Lock state for this handle */
-  AsyncLock *pLock;          /* AsyncLock object for this file system entry */
-  AsyncWrite closeOp;        /* Preallocated close operation */
-};
-
-/*
-** Add an entry to the end of the global write-op list. pWrite should point 
-** to an AsyncWrite structure allocated using sqlite3_malloc().  The writer
-** thread will call sqlite3_free() to free the structure after the specified
-** operation has been completed.
-**
-** Once an AsyncWrite structure has been added to the list, it becomes the
-** property of the writer thread and must not be read or modified by the
-** caller.  
-*/
-static void addAsyncWrite(AsyncWrite *pWrite){
-  /* We must hold the queue mutex in order to modify the queue pointers */
-  if( pWrite->op!=ASYNC_UNLOCK ){
-    async_mutex_enter(ASYNC_MUTEX_QUEUE);
-  }
-
-  /* Add the record to the end of the write-op queue */
-  assert( !pWrite->pNext );
-  if( async.pQueueLast ){
-    assert( async.pQueueFirst );
-    async.pQueueLast->pNext = pWrite;
-  }else{
-    async.pQueueFirst = pWrite;
-  }
-  async.pQueueLast = pWrite;
-  ASYNC_TRACE(("PUSH %p (%s %s %d)\n", pWrite, azOpcodeName[pWrite->op],
-         pWrite->pFileData ? pWrite->pFileData->zName : "-", pWrite->iOffset));
-
-  if( pWrite->op==ASYNC_CLOSE ){
-    async.nFile--;
-  }
-
-  /* The writer thread might have been idle because there was nothing
-  ** on the write-op queue for it to do.  So wake it up. */
-  async_cond_signal(ASYNC_COND_QUEUE);
-
-  /* Drop the queue mutex */
-  if( pWrite->op!=ASYNC_UNLOCK ){
-    async_mutex_leave(ASYNC_MUTEX_QUEUE);
-  }
-}
-
-/*
-** Increment async.nFile in a thread-safe manner.
-*/
-static void incrOpenFileCount(void){
-  /* We must hold the queue mutex in order to modify async.nFile */
-  async_mutex_enter(ASYNC_MUTEX_QUEUE);
-  if( async.nFile==0 ){
-    async.ioError = SQLITE_OK;
-  }
-  async.nFile++;
-  async_mutex_leave(ASYNC_MUTEX_QUEUE);
-}
-
-/*
-** This is a utility function to allocate and populate a new AsyncWrite
-** structure and insert it (via addAsyncWrite() ) into the global list.
-*/
-static int addNewAsyncWrite(
-  AsyncFileData *pFileData, 
-  int op, 
-  sqlite3_int64 iOffset, 
-  int nByte,
-  const char *zByte
-){
-  AsyncWrite *p;
-  if( op!=ASYNC_CLOSE && async.ioError ){
-    return async.ioError;
-  }
-  p = sqlite3_malloc(sizeof(AsyncWrite) + (zByte?nByte:0));
-  if( !p ){
-    /* The upper layer does not expect operations like OsWrite() to
-    ** return SQLITE_NOMEM. This is partly because under normal conditions
-    ** SQLite is required to do rollback without calling malloc(). So
-    ** if malloc() fails here, treat it as an I/O error. The above
-    ** layer knows how to handle that.
-    */
-    return SQLITE_IOERR;
-  }
-  p->op = op;
-  p->iOffset = iOffset;
-  p->nByte = nByte;
-  p->pFileData = pFileData;
-  p->pNext = 0;
-  if( zByte ){
-    p->zBuf = (char *)&p[1];
-    memcpy(p->zBuf, zByte, nByte);
-  }else{
-    p->zBuf = 0;
-  }
-  addAsyncWrite(p);
-  return SQLITE_OK;
-}
-
-/*
-** Close the file. This just adds an entry to the write-op list, the file is
-** not actually closed.
-*/
-static int asyncClose(sqlite3_file *pFile){
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-
-  /* Unlock the file, if it is locked */
-  async_mutex_enter(ASYNC_MUTEX_LOCK);
-  p->lock.eLock = 0;
-  async_mutex_leave(ASYNC_MUTEX_LOCK);
-
-  addAsyncWrite(&p->closeOp);
-  return SQLITE_OK;
-}
-
-/*
-** Implementation of sqlite3OsWrite() for asynchronous files. Instead of 
-** writing to the underlying file, this function adds an entry to the end of
-** the global AsyncWrite list. Either SQLITE_OK or SQLITE_NOMEM may be
-** returned.
-*/
-static int asyncWrite(
-  sqlite3_file *pFile, 
-  const void *pBuf, 
-  int amt, 
-  sqlite3_int64 iOff
-){
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-  return addNewAsyncWrite(p, ASYNC_WRITE, iOff, amt, pBuf);
-}
-
-/*
-** Read data from the file. First we read from the filesystem, then adjust 
-** the contents of the buffer based on ASYNC_WRITE operations in the 
-** write-op queue.
-**
-** This method holds the mutex from start to finish.
-*/
-static int asyncRead(
-  sqlite3_file *pFile, 
-  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 ){
-    AsyncWrite *pWrite;
-    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));
-        }
-      }
-    }
-  }
-
-asyncread_out:
-  async_mutex_leave(ASYNC_MUTEX_QUEUE);
-  return rc;
-}
-
-/*
-** Truncate the file to nByte bytes in length. This just adds an entry to 
-** the write-op list, no IO actually takes place.
-*/
-static int asyncTruncate(sqlite3_file *pFile, sqlite3_int64 nByte){
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-  return addNewAsyncWrite(p, ASYNC_TRUNCATE, nByte, 0, 0);
-}
-
-/*
-** Sync the file. This just adds an entry to the write-op list, the 
-** sync() is done later by sqlite3_async_flush().
-*/
-static int asyncSync(sqlite3_file *pFile, int flags){
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-  return addNewAsyncWrite(p, ASYNC_SYNC, 0, flags, 0);
-}
-
-/*
-** Read the size of the file. First we read the size of the file system 
-** entry, then adjust for any ASYNC_WRITE or ASYNC_TRUNCATE operations 
-** currently in the write-op list. 
-**
-** This method holds the mutex from start to finish.
-*/
-int asyncFileSize(sqlite3_file *pFile, sqlite3_int64 *piSize){
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-  int rc = SQLITE_OK;
-  sqlite3_int64 s = 0;
-  sqlite3_file *pBase;
-
-  async_mutex_enter(ASYNC_MUTEX_QUEUE);
-
-  /* Read the filesystem size from the base file. If pMethods is NULL, this
-  ** means the file hasn't been opened yet. In this case all relevant data 
-  ** must be in the write-op queue anyway, so we can omit reading from the
-  ** file-system.
-  */
-  pBase = p->pBaseRead;
-  if( pBase->pMethods ){
-    rc = pBase->pMethods->xFileSize(pBase, &s);
-  }
-
-  if( rc==SQLITE_OK ){
-    AsyncWrite *pWrite;
-    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
-      if( pWrite->op==ASYNC_DELETE 
-       && p->zName 
-       && strcmp(p->zName, pWrite->zBuf)==0 
-      ){
-        s = 0;
-      }else if( pWrite->pFileData && (
-          (pWrite->pFileData==p) 
-       || (p->zName && pWrite->pFileData->zName==p->zName) 
-      )){
-        switch( pWrite->op ){
-          case ASYNC_WRITE:
-            s = MAX(pWrite->iOffset + (sqlite3_int64)(pWrite->nByte), s);
-            break;
-          case ASYNC_TRUNCATE:
-            s = MIN(s, pWrite->iOffset);
-            break;
-        }
-      }
-    }
-    *piSize = s;
-  }
-  async_mutex_leave(ASYNC_MUTEX_QUEUE);
-  return rc;
-}
-
-/*
-** Lock or unlock the actual file-system entry.
-*/
-static int getFileLock(AsyncLock *pLock){
-  int rc = SQLITE_OK;
-  AsyncFileLock *pIter;
-  int eRequired = 0;
-
-  if( pLock->pFile ){
-    for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
-      assert(pIter->eAsyncLock>=pIter->eLock);
-      if( pIter->eAsyncLock>eRequired ){
-        eRequired = pIter->eAsyncLock;
-        assert(eRequired>=0 && eRequired<=SQLITE_LOCK_EXCLUSIVE);
-      }
-    }
-
-    if( eRequired>pLock->eLock ){
-      rc = pLock->pFile->pMethods->xLock(pLock->pFile, eRequired);
-      if( rc==SQLITE_OK ){
-        pLock->eLock = eRequired;
-      }
-    }
-    else if( eRequired<pLock->eLock && eRequired<=SQLITE_LOCK_SHARED ){
-      rc = pLock->pFile->pMethods->xUnlock(pLock->pFile, eRequired);
-      if( rc==SQLITE_OK ){
-        pLock->eLock = eRequired;
-      }
-    }
-  }
-
-  return rc;
-}
-
-/*
-** Return the AsyncLock structure from the global async.pLock list 
-** associated with the file-system entry identified by path zName 
-** (a string of nName bytes). If no such structure exists, return 0.
-*/
-static AsyncLock *findLock(const char *zName, int nName){
-  AsyncLock *p = async.pLock;
-  while( p && (p->nFile!=nName || memcmp(p->zFile, zName, nName)) ){
-    p = p->pNext;
-  }
-  return p;
-}
-
-/*
-** The following two methods - asyncLock() and asyncUnlock() - are used
-** to obtain and release locks on database files opened with the
-** asynchronous backend.
-*/
-static int asyncLock(sqlite3_file *pFile, int eLock){
-  int rc = SQLITE_OK;
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-
-  if( p->zName ){
-    async_mutex_enter(ASYNC_MUTEX_LOCK);
-    if( p->lock.eLock<eLock ){
-      AsyncLock *pLock = p->pLock;
-      AsyncFileLock *pIter;
-      assert(pLock && pLock->pList);
-      for(pIter=pLock->pList; pIter; pIter=pIter->pNext){
-        if( pIter!=&p->lock && (
-          (eLock==SQLITE_LOCK_EXCLUSIVE && pIter->eLock>=SQLITE_LOCK_SHARED) ||
-          (eLock==SQLITE_LOCK_PENDING && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
-          (eLock==SQLITE_LOCK_RESERVED && pIter->eLock>=SQLITE_LOCK_RESERVED) ||
-          (eLock==SQLITE_LOCK_SHARED && pIter->eLock>=SQLITE_LOCK_PENDING)
-        )){
-          rc = SQLITE_BUSY;
-        }
-      }
-      if( rc==SQLITE_OK ){
-        p->lock.eLock = eLock;
-        p->lock.eAsyncLock = MAX(p->lock.eAsyncLock, eLock);
-      }
-      assert(p->lock.eAsyncLock>=p->lock.eLock);
-      if( rc==SQLITE_OK ){
-        rc = getFileLock(pLock);
-      }
-    }
-    async_mutex_leave(ASYNC_MUTEX_LOCK);
-  }
-
-  ASYNC_TRACE(("LOCK %d (%s) rc=%d\n", eLock, p->zName, rc));
-  return rc;
-}
-static int asyncUnlock(sqlite3_file *pFile, int eLock){
-  int rc = SQLITE_OK;
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-  if( p->zName ){
-    AsyncFileLock *pLock = &p->lock;
-    async_mutex_enter(ASYNC_MUTEX_QUEUE);
-    async_mutex_enter(ASYNC_MUTEX_LOCK);
-    pLock->eLock = MIN(pLock->eLock, eLock);
-    rc = addNewAsyncWrite(p, ASYNC_UNLOCK, 0, eLock, 0);
-    async_mutex_leave(ASYNC_MUTEX_LOCK);
-    async_mutex_leave(ASYNC_MUTEX_QUEUE);
-  }
-  return rc;
-}
-
-/*
-** This function is called when the pager layer first opens a database file
-** and is checking for a hot-journal.
-*/
-static int asyncCheckReservedLock(sqlite3_file *pFile, int *pResOut){
-  int ret = 0;
-  AsyncFileLock *pIter;
-  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
-
-  async_mutex_enter(ASYNC_MUTEX_LOCK);
-  for(pIter=p->pLock->pList; pIter; pIter=pIter->pNext){
-    if( pIter->eLock>=SQLITE_LOCK_RESERVED ){
-      ret = 1;
-      break;
-    }
-  }
-  async_mutex_leave(ASYNC_MUTEX_LOCK);
-
-  ASYNC_TRACE(("CHECK-LOCK %d (%s)\n", ret, p->zName));
-  *pResOut = ret;
-  return SQLITE_OK;
-}
-
-/* 
-** sqlite3_file_control() implementation.
-*/
-static int asyncFileControl(sqlite3_file *id, int op, void *pArg){
-  switch( op ){
-    case SQLITE_FCNTL_LOCKSTATE: {
-      async_mutex_enter(ASYNC_MUTEX_LOCK);
-      *(int*)pArg = ((AsyncFile*)id)->pData->lock.eLock;
-      async_mutex_leave(ASYNC_MUTEX_LOCK);
-      return SQLITE_OK;
-    }
-  }
-  return SQLITE_ERROR;
-}
-
-/* 
-** Return the device characteristics and sector-size of the device. It
-** is tricky to implement these correctly, as this backend might 
-** not have an open file handle at this point.
-*/
-static int asyncSectorSize(sqlite3_file *pFile){
-  UNUSED_PARAMETER(pFile);
-  return 512;
-}
-static int asyncDeviceCharacteristics(sqlite3_file *pFile){
-  UNUSED_PARAMETER(pFile);
-  return 0;
-}
-
-static int unlinkAsyncFile(AsyncFileData *pData){
-  AsyncFileLock **ppIter;
-  int rc = SQLITE_OK;
-
-  if( pData->zName ){
-    AsyncLock *pLock = pData->pLock;
-    for(ppIter=&pLock->pList; *ppIter; ppIter=&((*ppIter)->pNext)){
-      if( (*ppIter)==&pData->lock ){
-        *ppIter = pData->lock.pNext;
-        break;
-      }
-    }
-    if( !pLock->pList ){
-      AsyncLock **pp;
-      if( pLock->pFile ){
-        pLock->pFile->pMethods->xClose(pLock->pFile);
-      }
-      for(pp=&async.pLock; *pp!=pLock; pp=&((*pp)->pNext));
-      *pp = pLock->pNext;
-      sqlite3_free(pLock);
-    }else{
-      rc = getFileLock(pLock);
-    }
-  }
-
-  return rc;
-}
-
-/*
-** The parameter passed to this function is a copy of a 'flags' parameter
-** passed to this modules xOpen() method. This function returns true
-** if the file should be opened asynchronously, or false if it should
-** be opened immediately.
-**
-** If the file is to be opened asynchronously, then asyncOpen() will add
-** an entry to the event queue and the file will not actually be opened
-** until the event is processed. Otherwise, the file is opened directly
-** by the caller.
-*/
-static int doAsynchronousOpen(int flags){
-  return (flags&SQLITE_OPEN_CREATE) && (
-      (flags&SQLITE_OPEN_MAIN_JOURNAL) ||
-      (flags&SQLITE_OPEN_TEMP_JOURNAL) ||
-      (flags&SQLITE_OPEN_DELETEONCLOSE)
-  );
-}
-
-/*
-** Open a file.
-*/
-static int asyncOpen(
-  sqlite3_vfs *pAsyncVfs,
-  const char *zName,
-  sqlite3_file *pFile,
-  int flags,
-  int *pOutFlags
-){
-  static sqlite3_io_methods async_methods = {
-    1,                               /* iVersion */
-    asyncClose,                      /* xClose */
-    asyncRead,                       /* xRead */
-    asyncWrite,                      /* xWrite */
-    asyncTruncate,                   /* xTruncate */
-    asyncSync,                       /* xSync */
-    asyncFileSize,                   /* xFileSize */
-    asyncLock,                       /* xLock */
-    asyncUnlock,                     /* xUnlock */
-    asyncCheckReservedLock,          /* xCheckReservedLock */
-    asyncFileControl,                /* xFileControl */
-    asyncSectorSize,                 /* xSectorSize */
-    asyncDeviceCharacteristics       /* xDeviceCharacteristics */
-  };
-
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  AsyncFile *p = (AsyncFile *)pFile;
-  int nName = 0;
-  int rc = SQLITE_OK;
-  int nByte;
-  AsyncFileData *pData;
-  AsyncLock *pLock = 0;
-  char *z;
-  int isAsyncOpen = doAsynchronousOpen(flags);
-
-  /* If zName is NULL, then the upper layer is requesting an anonymous file */
-  if( zName ){
-    nName = (int)strlen(zName)+1;
-  }
-
-  nByte = (
-    sizeof(AsyncFileData) +        /* AsyncFileData structure */
-    2 * pVfs->szOsFile +           /* AsyncFileData.pBaseRead and pBaseWrite */
-    nName                          /* AsyncFileData.zName */
-  ); 
-  z = sqlite3_malloc(nByte);
-  if( !z ){
-    return SQLITE_NOMEM;
-  }
-  memset(z, 0, nByte);
-  pData = (AsyncFileData*)z;
-  z += sizeof(pData[0]);
-  pData->pBaseRead = (sqlite3_file*)z;
-  z += pVfs->szOsFile;
-  pData->pBaseWrite = (sqlite3_file*)z;
-  pData->closeOp.pFileData = pData;
-  pData->closeOp.op = ASYNC_CLOSE;
-
-  if( zName ){
-    z += pVfs->szOsFile;
-    pData->zName = z;
-    pData->nName = nName;
-    memcpy(pData->zName, zName, nName);
-  }
-
-  if( !isAsyncOpen ){
-    int flagsout;
-    rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, &flagsout);
-    if( rc==SQLITE_OK 
-     && (flagsout&SQLITE_OPEN_READWRITE) 
-     && (flags&SQLITE_OPEN_EXCLUSIVE)==0
-    ){
-      rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseWrite, flags, 0);
-    }
-    if( pOutFlags ){
-      *pOutFlags = flagsout;
-    }
-  }
-
-  async_mutex_enter(ASYNC_MUTEX_LOCK);
-
-  if( zName && rc==SQLITE_OK ){
-    pLock = findLock(pData->zName, pData->nName);
-    if( !pLock ){
-      int nByte = pVfs->szOsFile + sizeof(AsyncLock) + pData->nName + 1; 
-      pLock = (AsyncLock *)sqlite3_malloc(nByte);
-      if( pLock ){
-        memset(pLock, 0, nByte);
-        if( async.bLockFiles && (flags&SQLITE_OPEN_MAIN_DB) ){
-          pLock->pFile = (sqlite3_file *)&pLock[1];
-          rc = pVfs->xOpen(pVfs, pData->zName, pLock->pFile, flags, 0);
-          if( rc!=SQLITE_OK ){
-            sqlite3_free(pLock);
-            pLock = 0;
-          }
-        }
-        if( pLock ){
-          pLock->nFile = pData->nName;
-          pLock->zFile = &((char *)(&pLock[1]))[pVfs->szOsFile];
-          memcpy(pLock->zFile, pData->zName, pLock->nFile);
-          pLock->pNext = async.pLock;
-          async.pLock = pLock;
-        }
-      }else{
-        rc = SQLITE_NOMEM;
-      }
-    }
-  }
-
-  if( rc==SQLITE_OK ){
-    p->pMethod = &async_methods;
-    p->pData = pData;
-
-    /* Link AsyncFileData.lock into the linked list of 
-    ** AsyncFileLock structures for this file.
-    */
-    if( zName ){
-      pData->lock.pNext = pLock->pList;
-      pLock->pList = &pData->lock;
-      pData->zName = pLock->zFile;
-    }
-  }else{
-    if( pData->pBaseRead->pMethods ){
-      pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
-    }
-    if( pData->pBaseWrite->pMethods ){
-      pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
-    }
-    sqlite3_free(pData);
-  }
-
-  async_mutex_leave(ASYNC_MUTEX_LOCK);
-
-  if( rc==SQLITE_OK ){
-    incrOpenFileCount();
-    pData->pLock = pLock;
-  }
-
-  if( rc==SQLITE_OK && isAsyncOpen ){
-    rc = addNewAsyncWrite(pData, ASYNC_OPENEXCLUSIVE, (sqlite3_int64)flags,0,0);
-    if( rc==SQLITE_OK ){
-      if( pOutFlags ) *pOutFlags = flags;
-    }else{
-      async_mutex_enter(ASYNC_MUTEX_LOCK);
-      unlinkAsyncFile(pData);
-      async_mutex_leave(ASYNC_MUTEX_LOCK);
-      sqlite3_free(pData);
-    }
-  }
-  if( rc!=SQLITE_OK ){
-    p->pMethod = 0;
-  }
-  return rc;
-}
-
-/*
-** Implementation of sqlite3OsDelete. Add an entry to the end of the 
-** write-op queue to perform the delete.
-*/
-static int asyncDelete(sqlite3_vfs *pAsyncVfs, const char *z, int syncDir){
-  UNUSED_PARAMETER(pAsyncVfs);
-  return addNewAsyncWrite(0, ASYNC_DELETE, syncDir, (int)strlen(z)+1, z);
-}
-
-/*
-** Implementation of sqlite3OsAccess. This method holds the mutex from
-** start to finish.
-*/
-static int asyncAccess(
-  sqlite3_vfs *pAsyncVfs, 
-  const char *zName, 
-  int flags,
-  int *pResOut
-){
-  int rc;
-  int ret;
-  AsyncWrite *p;
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-
-  assert(flags==SQLITE_ACCESS_READWRITE 
-      || flags==SQLITE_ACCESS_READ 
-      || flags==SQLITE_ACCESS_EXISTS 
-  );
-
-  async_mutex_enter(ASYNC_MUTEX_QUEUE);
-  rc = pVfs->xAccess(pVfs, zName, flags, &ret);
-  if( rc==SQLITE_OK && flags==SQLITE_ACCESS_EXISTS ){
-    for(p=async.pQueueFirst; p; p = p->pNext){
-      if( p->op==ASYNC_DELETE && 0==strcmp(p->zBuf, zName) ){
-        ret = 0;
-      }else if( p->op==ASYNC_OPENEXCLUSIVE 
-             && p->pFileData->zName
-             && 0==strcmp(p->pFileData->zName, zName) 
-      ){
-        ret = 1;
-      }
-    }
-  }
-  ASYNC_TRACE(("ACCESS(%s): %s = %d\n", 
-    flags==SQLITE_ACCESS_READWRITE?"read-write":
-    flags==SQLITE_ACCESS_READ?"read":"exists"
-    , zName, ret)
-  );
-  async_mutex_leave(ASYNC_MUTEX_QUEUE);
-  *pResOut = ret;
-  return rc;
-}
-
-/*
-** Fill in zPathOut with the full path to the file identified by zPath.
-*/
-static int asyncFullPathname(
-  sqlite3_vfs *pAsyncVfs, 
-  const char *zPath, 
-  int nPathOut,
-  char *zPathOut
-){
-  int rc;
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  rc = pVfs->xFullPathname(pVfs, zPath, nPathOut, zPathOut);
-
-  /* Because of the way intra-process file locking works, this backend
-  ** needs to return a canonical path. The following block assumes the
-  ** file-system uses unix style paths. 
-  */
-  if( rc==SQLITE_OK ){
-    int i, j;
-    int n = nPathOut;
-    char *z = zPathOut;
-    while( n>1 && z[n-1]=='/' ){ n--; }
-    for(i=j=0; i<n; i++){
-      if( z[i]=='/' ){
-        if( z[i+1]=='/' ) continue;
-        if( z[i+1]=='.' && i+2<n && z[i+2]=='/' ){
-          i += 1;
-          continue;
-        }
-        if( z[i+1]=='.' && i+3<n && z[i+2]=='.' && z[i+3]=='/' ){
-          while( j>0 && z[j-1]!='/' ){ j--; }
-          if( j>0 ){ j--; }
-          i += 2;
-          continue;
-        }
-      }
-      z[j++] = z[i];
-    }
-    z[j] = 0;
-  }
-
-  return rc;
-}
-static void *asyncDlOpen(sqlite3_vfs *pAsyncVfs, const char *zPath){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  return pVfs->xDlOpen(pVfs, zPath);
-}
-static void asyncDlError(sqlite3_vfs *pAsyncVfs, int nByte, char *zErrMsg){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  pVfs->xDlError(pVfs, nByte, zErrMsg);
-}
-static void (*asyncDlSym(
-  sqlite3_vfs *pAsyncVfs, 
-  void *pHandle, 
-  const char *zSymbol
-))(void){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  return pVfs->xDlSym(pVfs, pHandle, zSymbol);
-}
-static void asyncDlClose(sqlite3_vfs *pAsyncVfs, void *pHandle){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  pVfs->xDlClose(pVfs, pHandle);
-}
-static int asyncRandomness(sqlite3_vfs *pAsyncVfs, int nByte, char *zBufOut){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  return pVfs->xRandomness(pVfs, nByte, zBufOut);
-}
-static int asyncSleep(sqlite3_vfs *pAsyncVfs, int nMicro){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  return pVfs->xSleep(pVfs, nMicro);
-}
-static int asyncCurrentTime(sqlite3_vfs *pAsyncVfs, double *pTimeOut){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)pAsyncVfs->pAppData;
-  return pVfs->xCurrentTime(pVfs, pTimeOut);
-}
-
-static sqlite3_vfs async_vfs = {
-  1,                    /* iVersion */
-  sizeof(AsyncFile),    /* szOsFile */
-  0,                    /* mxPathname */
-  0,                    /* pNext */
-  SQLITEASYNC_VFSNAME,  /* zName */
-  0,                    /* pAppData */
-  asyncOpen,            /* xOpen */
-  asyncDelete,          /* xDelete */
-  asyncAccess,          /* xAccess */
-  asyncFullPathname,    /* xFullPathname */
-  asyncDlOpen,          /* xDlOpen */
-  asyncDlError,         /* xDlError */
-  asyncDlSym,           /* xDlSym */
-  asyncDlClose,         /* xDlClose */
-  asyncRandomness,      /* xDlError */
-  asyncSleep,           /* xDlSym */
-  asyncCurrentTime      /* xDlClose */
-};
-
-/* 
-** This procedure runs in a separate thread, reading messages off of the
-** write queue and processing them one by one.  
-**
-** If async.writerHaltNow is true, then this procedure exits
-** after processing a single message.
-**
-** If async.writerHaltWhenIdle is true, then this procedure exits when
-** the write queue is empty.
-**
-** If both of the above variables are false, this procedure runs
-** indefinately, waiting for operations to be added to the write queue
-** and processing them in the order in which they arrive.
-**
-** An artifical delay of async.ioDelay milliseconds is inserted before
-** each write operation in order to simulate the effect of a slow disk.
-**
-** Only one instance of this procedure may be running at a time.
-*/
-static void asyncWriterThread(void){
-  sqlite3_vfs *pVfs = (sqlite3_vfs *)(async_vfs.pAppData);
-  AsyncWrite *p = 0;
-  int rc = SQLITE_OK;
-  int holdingMutex = 0;
-
-  async_mutex_enter(ASYNC_MUTEX_WRITER);
-
-  while( async.eHalt!=SQLITEASYNC_HALT_NOW ){
-    int doNotFree = 0;
-    sqlite3_file *pBase = 0;
-
-    if( !holdingMutex ){
-      async_mutex_enter(ASYNC_MUTEX_QUEUE);
-    }
-    while( (p = async.pQueueFirst)==0 ){
-      if( async.eHalt!=SQLITEASYNC_HALT_NEVER ){
-        async_mutex_leave(ASYNC_MUTEX_QUEUE);
-        break;
-      }else{
-        ASYNC_TRACE(("IDLE\n"));
-        async_cond_wait(ASYNC_COND_QUEUE, ASYNC_MUTEX_QUEUE);
-        ASYNC_TRACE(("WAKEUP\n"));
-      }
-    }
-    if( p==0 ) break;
-    holdingMutex = 1;
-
-    /* Right now this thread is holding the mutex on the write-op queue.
-    ** Variable 'p' points to the first entry in the write-op queue. In
-    ** the general case, we hold on to the mutex for the entire body of
-    ** the loop. 
-    **
-    ** However in the cases enumerated below, we relinquish the mutex,
-    ** perform the IO, and then re-request the mutex before removing 'p' from
-    ** the head of the write-op queue. The idea is to increase concurrency with
-    ** sqlite threads.
-    **
-    **     * An ASYNC_CLOSE operation.
-    **     * An ASYNC_OPENEXCLUSIVE operation. For this one, we relinquish 
-    **       the mutex, call the underlying xOpenExclusive() function, then
-    **       re-aquire the mutex before seting the AsyncFile.pBaseRead 
-    **       variable.
-    **     * ASYNC_SYNC and ASYNC_WRITE operations, if 
-    **       SQLITE_ASYNC_TWO_FILEHANDLES was set at compile time and two
-    **       file-handles are open for the particular file being "synced".
-    */
-    if( async.ioError!=SQLITE_OK && p->op!=ASYNC_CLOSE ){
-      p->op = ASYNC_NOOP;
-    }
-    if( p->pFileData ){
-      pBase = p->pFileData->pBaseWrite;
-      if( 
-        p->op==ASYNC_CLOSE || 
-        p->op==ASYNC_OPENEXCLUSIVE ||
-        (pBase->pMethods && (p->op==ASYNC_SYNC || p->op==ASYNC_WRITE) ) 
-      ){
-        async_mutex_leave(ASYNC_MUTEX_QUEUE);
-        holdingMutex = 0;
-      }
-      if( !pBase->pMethods ){
-        pBase = p->pFileData->pBaseRead;
-      }
-    }
-
-    switch( p->op ){
-      case ASYNC_NOOP:
-        break;
-
-      case ASYNC_WRITE:
-        assert( pBase );
-        ASYNC_TRACE(("WRITE %s %d bytes at %d\n",
-                p->pFileData->zName, p->nByte, p->iOffset));
-        rc = pBase->pMethods->xWrite(pBase, (void *)(p->zBuf), p->nByte, p->iOffset);
-        break;
-
-      case ASYNC_SYNC:
-        assert( pBase );
-        ASYNC_TRACE(("SYNC %s\n", p->pFileData->zName));
-        rc = pBase->pMethods->xSync(pBase, p->nByte);
-        break;
-
-      case ASYNC_TRUNCATE:
-        assert( pBase );
-        ASYNC_TRACE(("TRUNCATE %s to %d bytes\n", 
-                p->pFileData->zName, p->iOffset));
-        rc = pBase->pMethods->xTruncate(pBase, p->iOffset);
-        break;
-
-      case ASYNC_CLOSE: {
-        AsyncFileData *pData = p->pFileData;
-        ASYNC_TRACE(("CLOSE %s\n", p->pFileData->zName));
-        if( pData->pBaseWrite->pMethods ){
-          pData->pBaseWrite->pMethods->xClose(pData->pBaseWrite);
-        }
-        if( pData->pBaseRead->pMethods ){
-          pData->pBaseRead->pMethods->xClose(pData->pBaseRead);
-        }
-
-        /* Unlink AsyncFileData.lock from the linked list of AsyncFileLock 
-        ** structures for this file. Obtain the async.lockMutex mutex 
-        ** before doing so.
-        */
-        async_mutex_enter(ASYNC_MUTEX_LOCK);
-        rc = unlinkAsyncFile(pData);
-        async_mutex_leave(ASYNC_MUTEX_LOCK);
-
-        if( !holdingMutex ){
-          async_mutex_enter(ASYNC_MUTEX_QUEUE);
-          holdingMutex = 1;
-        }
-        assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
-        async.pQueueFirst = p->pNext;
-        sqlite3_free(pData);
-        doNotFree = 1;
-        break;
-      }
-
-      case ASYNC_UNLOCK: {
-        AsyncWrite *pIter;
-        AsyncFileData *pData = p->pFileData;
-        int eLock = p->nByte;
-
-        /* When a file is locked by SQLite using the async backend, it is 
-        ** locked within the 'real' file-system synchronously. When it is
-        ** unlocked, an ASYNC_UNLOCK event is added to the write-queue to
-        ** unlock the file asynchronously. The design of the async backend
-        ** requires that the 'real' file-system file be locked from the
-        ** time that SQLite first locks it (and probably reads from it)
-        ** until all asynchronous write events that were scheduled before
-        ** SQLite unlocked the file have been processed.
-        **
-        ** This is more complex if SQLite locks and unlocks the file multiple
-        ** times in quick succession. For example, if SQLite does: 
-        ** 
-        **   lock, write, unlock, lock, write, unlock
-        **
-        ** Each "lock" operation locks the file immediately. Each "write" 
-        ** and "unlock" operation adds an event to the event queue. If the
-        ** second "lock" operation is performed before the first "unlock"
-        ** operation has been processed asynchronously, then the first
-        ** "unlock" cannot be safely processed as is, since this would mean
-        ** the file was unlocked when the second "write" operation is
-        ** processed. To work around this, when processing an ASYNC_UNLOCK
-        ** operation, SQLite:
-        **
-        **   1) Unlocks the file to the minimum of the argument passed to
-        **      the xUnlock() call and the current lock from SQLite's point
-        **      of view, and
-        **
-        **   2) Only unlocks the file at all if this event is the last
-        **      ASYNC_UNLOCK event on this file in the write-queue.
-        */ 
-        assert( holdingMutex==1 );
-        assert( async.pQueueFirst==p );
-        for(pIter=async.pQueueFirst->pNext; pIter; pIter=pIter->pNext){
-          if( pIter->pFileData==pData && pIter->op==ASYNC_UNLOCK ) break;
-        }
-        if( !pIter ){
-          async_mutex_enter(ASYNC_MUTEX_LOCK);
-          pData->lock.eAsyncLock = MIN(
-              pData->lock.eAsyncLock, MAX(pData->lock.eLock, eLock)
-          );
-          assert(pData->lock.eAsyncLock>=pData->lock.eLock);
-          rc = getFileLock(pData->pLock);
-          async_mutex_leave(ASYNC_MUTEX_LOCK);
-        }
-        break;
-      }
-
-      case ASYNC_DELETE:
-        ASYNC_TRACE(("DELETE %s\n", p->zBuf));
-        rc = pVfs->xDelete(pVfs, p->zBuf, (int)p->iOffset);
-        break;
-
-      case ASYNC_OPENEXCLUSIVE: {
-        int flags = (int)p->iOffset;
-        AsyncFileData *pData = p->pFileData;
-        ASYNC_TRACE(("OPEN %s flags=%d\n", p->zBuf, (int)p->iOffset));
-        assert(pData->pBaseRead->pMethods==0 && pData->pBaseWrite->pMethods==0);
-        rc = pVfs->xOpen(pVfs, pData->zName, pData->pBaseRead, flags, 0);
-        assert( holdingMutex==0 );
-        async_mutex_enter(ASYNC_MUTEX_QUEUE);
-        holdingMutex = 1;
-        break;
-      }
-
-      default: assert(!"Illegal value for AsyncWrite.op");
-    }
-
-    /* If we didn't hang on to the mutex during the IO op, obtain it now
-    ** so that the AsyncWrite structure can be safely removed from the 
-    ** global write-op queue.
-    */
-    if( !holdingMutex ){
-      async_mutex_enter(ASYNC_MUTEX_QUEUE);
-      holdingMutex = 1;
-    }
-    /* ASYNC_TRACE(("UNLINK %p\n", p)); */
-    if( p==async.pQueueLast ){
-      async.pQueueLast = 0;
-    }
-    if( !doNotFree ){
-      assert_mutex_is_held(ASYNC_MUTEX_QUEUE);
-      async.pQueueFirst = p->pNext;
-      sqlite3_free(p);
-    }
-    assert( holdingMutex );
-
-    /* An IO error has occurred. We cannot report the error back to the
-    ** connection that requested the I/O since the error happened 
-    ** asynchronously.  The connection has already moved on.  There 
-    ** really is nobody to report the error to.
-    **
-    ** The file for which the error occurred may have been a database or
-    ** journal file. Regardless, none of the currently queued operations
-    ** associated with the same database should now be performed. Nor should
-    ** any subsequently requested IO on either a database or journal file 
-    ** handle for the same database be accepted until the main database
-    ** file handle has been closed and reopened.
-    **
-    ** Furthermore, no further IO should be queued or performed on any file
-    ** handle associated with a database that may have been part of a 
-    ** multi-file transaction that included the database associated with 
-    ** the IO error (i.e. a database ATTACHed to the same handle at some 
-    ** point in time).
-    */
-    if( rc!=SQLITE_OK ){
-      async.ioError = rc;
-    }
-
-    if( async.ioError && !async.pQueueFirst ){
-      async_mutex_enter(ASYNC_MUTEX_LOCK);
-      if( 0==async.pLock ){
-        async.ioError = SQLITE_OK;
-      }
-      async_mutex_leave(ASYNC_MUTEX_LOCK);
-    }
-
-    /* Drop the queue mutex before continuing to the next write operation
-    ** in order to give other threads a chance to work with the write queue.
-    */
-    if( !async.pQueueFirst || !async.ioError ){
-      async_mutex_leave(ASYNC_MUTEX_QUEUE);
-      holdingMutex = 0;
-      if( async.ioDelay>0 ){
-        pVfs->xSleep(pVfs, async.ioDelay*1000);
-      }else{
-        async_sched_yield();
-      }
-    }
-  }
-  
-  async_mutex_leave(ASYNC_MUTEX_WRITER);
-  return;
-}
-
-/*
-** Install the asynchronous VFS.
-*/ 
-int sqlite3async_initialize(const char *zParent, int isDefault){
-  int rc = SQLITE_OK;
-  if( async_vfs.pAppData==0 ){
-    sqlite3_vfs *pParent = sqlite3_vfs_find(zParent);
-    if( !pParent || async_os_initialize() ){
-      rc = SQLITE_ERROR;
-    }else if( SQLITE_OK!=(rc = sqlite3_vfs_register(&async_vfs, isDefault)) ){
-      async_os_shutdown();
-    }else{
-      async_vfs.pAppData = (void *)pParent;
-      async_vfs.mxPathname = ((sqlite3_vfs *)async_vfs.pAppData)->mxPathname;
-    }
-  }
-  return rc;
-}
-
-/*
-** Uninstall the asynchronous VFS.
-*/
-void sqlite3async_shutdown(void){
-  if( async_vfs.pAppData ){
-    async_os_shutdown();
-    sqlite3_vfs_unregister((sqlite3_vfs *)&async_vfs);
-    async_vfs.pAppData = 0;
-  }
-}
-
-/*
-** Process events on the write-queue.
-*/
-void sqlite3async_run(void){
-  asyncWriterThread();
-}
-
-/*
-** Control/configure the asynchronous IO system.
-*/
-int sqlite3async_control(int op, ...){
-  va_list ap;
-  va_start(ap, op);
-  switch( op ){
-    case SQLITEASYNC_HALT: {
-      int eWhen = va_arg(ap, int);
-      if( eWhen!=SQLITEASYNC_HALT_NEVER
-       && eWhen!=SQLITEASYNC_HALT_NOW
-       && eWhen!=SQLITEASYNC_HALT_IDLE
-      ){
-        return SQLITE_MISUSE;
-      }
-      async.eHalt = eWhen;
-      async_mutex_enter(ASYNC_MUTEX_QUEUE);
-      async_cond_signal(ASYNC_COND_QUEUE);
-      async_mutex_leave(ASYNC_MUTEX_QUEUE);
-      break;
-    }
-
-    case SQLITEASYNC_DELAY: {
-      int iDelay = va_arg(ap, int);
-      if( iDelay<0 ){
-        return SQLITE_MISUSE;
-      }
-      async.ioDelay = iDelay;
-      break;
-    }
-
-    case SQLITEASYNC_LOCKFILES: {
-      int bLock = va_arg(ap, int);
-      async_mutex_enter(ASYNC_MUTEX_QUEUE);
-      if( async.nFile || async.pQueueFirst ){
-        async_mutex_leave(ASYNC_MUTEX_QUEUE);
-        return SQLITE_MISUSE;
-      }
-      async.bLockFiles = bLock;
-      async_mutex_leave(ASYNC_MUTEX_QUEUE);
-      break;
-    }
-      
-    case SQLITEASYNC_GET_HALT: {
-      int *peWhen = va_arg(ap, int *);
-      *peWhen = async.eHalt;
-      break;
-    }
-    case SQLITEASYNC_GET_DELAY: {
-      int *piDelay = va_arg(ap, int *);
-      *piDelay = async.ioDelay;
-      break;
-    }
-    case SQLITEASYNC_GET_LOCKFILES: {
-      int *piDelay = va_arg(ap, int *);
-      *piDelay = async.bLockFiles;
-      break;
-    }
-
-    default:
-      return SQLITE_ERROR;
-  }
-  return SQLITE_OK;
-}
-
-#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_ASYNCIO) */
-