SQLite

/*
** 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: test_async.c,v 1.55 2009/03/28 17:21:52 danielk1977 Exp $
**
** This file contains an example implementation of an asynchronous IO 
** backend for SQLite.
**
** WHAT IS ASYNCHRONOUS I/O?
**
** With asynchronous I/O, write requests are handled by a separate thread

  assert(&(aMutex[1])==&async.queueMutex);
  assert(&(aMutex[2])==&async.writerMutex);
  assert(&(aHolder[0])==&asyncdebug.lockMutexHolder);
  assert(&(aHolder[1])==&asyncdebug.queueMutexHolder);
  assert(&(aHolder[2])==&asyncdebug.writerMutexHolder);

  assert( pthread_self()!=0 );

  for(iIdx=0; iIdx<3; iIdx++){
    if( pMutex==&aMutex[iIdx] ) break;

    /* This is the key assert(). Here we are checking that if the caller
     * is trying to block on async.writerMutex, neither of the other two
     * mutex are held. If the caller is trying to block on async.queueMutex,
     * lockMutex is not held.

**
** 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 ){
    pthread_mutex_lock(&async.queueMutex);
  }

  /* 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--;
  }

  /* Drop the queue mutex */
  if( pWrite->op!=ASYNC_UNLOCK ){
    pthread_mutex_unlock(&async.queueMutex);
  }

  /* The writer thread might have been idle because there was nothing
  ** on the write-op queue for it to do.  So wake it up. */
  pthread_cond_signal(&async.queueSignal);
}

/*

  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;
    pthread_mutex_lock(&async.queueMutex);
    pthread_mutex_lock(&async.lockMutex);
    pLock->eLock = MIN(pLock->eLock, eLock);

    rc = addNewAsyncWrite(p, ASYNC_UNLOCK, 0, eLock, 0);
    pthread_mutex_unlock(&async.lockMutex);
    pthread_mutex_unlock(&async.queueMutex);
  }
  return rc;
}

/*
** This function is called when the pager layer first opens a database file
** and is checking for a hot-journal.

        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 ){
          pthread_mutex_lock(&async.lockMutex);
          pData->lock.eAsyncLock = MIN(
              pData->lock.eAsyncLock, MAX(pData->lock.eLock, eLock)
          );
          assert(pData->lock.eAsyncLock>=pData->lock.eLock);
          rc = getFileLock(pData->pLock);
          pthread_mutex_unlock(&async.lockMutex);
        }
        break;
      }

      case ASYNC_DELETE:
        ASYNC_TRACE(("DELETE %s\n", p->zBuf));
        rc = pVfs->xDelete(pVfs, p->zBuf, (int)p->iOffset);
        break;

******************************************************************************
**
** This file contains code for a VFS layer that acts as a wrapper around
** an existing VFS. The code in this file attempts to verify that SQLite
** correctly populates and syncs a journal file before writing to a
** corresponding database file.
**
** $Id: test_journal.c,v 1.14 2009/03/28 17:21:52 danielk1977 Exp $
*/
#if SQLITE_TEST          /* This file is used for testing only */

#include "sqlite3.h"
#include "sqliteInt.h"

/*

};

struct JtGlobal {
  sqlite3_vfs *pVfs;             /* Parent VFS */
  jt_file *pList;                /* List of all open files */
};
static struct JtGlobal g = {0, 0};

/*
** Functions to obtain and relinquish a mutex to protect g.pList. The
** STATIC_PRNG mutex is reused, purely for the sake of convenience.
*/
static void enterJtMutex(void){
  sqlite3_mutex_enter(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
}
static void leaveJtMutex(void){
  sqlite3_mutex_leave(sqlite3_mutex_alloc(SQLITE_MUTEX_STATIC_PRNG));
}

extern int sqlite3_io_error_pending;
static void stop_ioerr_simulation(int *piSave){
  *piSave = sqlite3_io_error_pending;
  sqlite3_io_error_pending = -1;
}
static void start_ioerr_simulation(int iSave){

** Close an jt-file.
*/
static int jtClose(sqlite3_file *pFile){
  jt_file **pp;
  jt_file *p = (jt_file *)pFile;

  closeTransaction(p);
  enterJtMutex();
  if( p->zName ){
    for(pp=&g.pList; *pp!=p; pp=&(*pp)->pNext);
    *pp = p->pNext;
  }
  leaveJtMutex();
  return sqlite3OsClose(p->pReal);
}

/*
** Read data from an jt-file.
*/
static int jtRead(
  sqlite3_file *pFile, 
  void *zBuf, 
  int iAmt, 
  sqlite_int64 iOfst
){
  jt_file *p = (jt_file *)pFile;
  return sqlite3OsRead(p->pReal, zBuf, iAmt, iOfst);
}


/*
** Parameter zJournal is the name of a journal file that is currently 
** open. This function locates and returns the handle opened on the
** corresponding database file by the pager that currently has the
** journal file opened. This file-handle is identified by the 
** following properties:
**
**   a) SQLITE_OPEN_MAIN_DB was specified when the file was opened.
**
**   b) The file-name specified when the file was opened matches
**      all but the final 8 characters of the journal file name.
**
**   c) There is currently a reserved lock on the file.
**/
static jt_file *locateDatabaseHandle(const char *zJournal){
  jt_file *pMain = 0;
  enterJtMutex();
  for(pMain=g.pList; pMain; pMain=pMain->pNext){
    int nName = strlen(zJournal) - strlen("-journal");
    if( (pMain->flags&SQLITE_OPEN_MAIN_DB)
     && (strlen(pMain->zName)==nName)
     && 0==memcmp(pMain->zName, zJournal, nName)
     && (pMain->eLock>=SQLITE_LOCK_RESERVED)
    ){
      break;
    }
  }
  leaveJtMutex();
  return pMain;
}

/*
** Parameter z points to a buffer of 4 bytes in size containing a 
** unsigned 32-bit integer stored in big-endian format. Decode the 
** integer and return its value.

    pFile->pMethods = &jt_io_methods;
    p->eLock = 0;
    p->zName = zName;
    p->flags = flags;
    p->pNext = 0;
    p->pWritable = 0;
    p->aCksum = 0;
    enterJtMutex();
    if( zName ){
      p->pNext = g.pList;
      g.pList = p;
    }
    leaveJtMutex();
  }
  return rc;
}

/*
** Delete the file located at zPath. If the dirSync argument is true,
** ensure the file-system modifications are synced to disk before