test_async.c

最新的sqlite3.6.2源代码

**     async.queueMutex
**     async.writerMutex
**     async.lockMutex
**
** If NDEBUG is defined, these wrappers do nothing except call the 
** corresponding pthreads function. If NDEBUG is not defined, then the
** following variables are used to store the thread-id (as returned
** by pthread_self()) currently holding the mutex, or 0 otherwise:
**
**     asyncdebug.queueMutexHolder
**     asyncdebug.writerMutexHolder
**     asyncdebug.lockMutexHolder
**
** These variables are used by some assert() statements that verify
** the statements made in the "Deadlock Prevention" notes earlier
** in this file.
*/
#ifndef NDEBUG

static struct TestAsyncDebugData {
  pthread_t lockMutexHolder;
  pthread_t queueMutexHolder;
  pthread_t writerMutexHolder;
} asyncdebug = {0, 0, 0};

/*
** Wrapper around pthread_mutex_lock(). Checks that we have not violated
** the anti-deadlock rules (see "Deadlock prevention" above).
*/
static int async_mutex_lock(pthread_mutex_t *pMutex){
  int iIdx;
  int rc;
  pthread_mutex_t *aMutex = (pthread_mutex_t *)(&async);
  pthread_t *aHolder = (pthread_t *)(&asyncdebug);

  /* The code in this 'ifndef NDEBUG' block depends on a certain alignment
   * of the variables in TestAsyncStaticData and TestAsyncDebugData. The
   * following assert() statements check that this has not been changed.
   *
   * Really, these only need to be run once at startup time.
   */
  assert(&(aMutex[0])==&async.lockMutex);
  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.
     */
    assert(!pthread_equal(aHolder[iIdx], pthread_self()));
  }
  assert(iIdx<3);

  rc = pthread_mutex_lock(pMutex);
  if( rc==0 ){
    assert(aHolder[iIdx]==0);
    aHolder[iIdx] = pthread_self();
  }
  return rc;
}

/*
** Wrapper around pthread_mutex_unlock().
*/
static int async_mutex_unlock(pthread_mutex_t *pMutex){
  int iIdx;
  int rc;
  pthread_mutex_t *aMutex = (pthread_mutex_t *)(&async);
  pthread_t *aHolder = (pthread_t *)(&asyncdebug);

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

  assert(pthread_equal(aHolder[iIdx], pthread_self()));
  aHolder[iIdx] = 0;
  rc = pthread_mutex_unlock(pMutex);
  assert(rc==0);

  return 0;
}

/*
** Wrapper around pthread_mutex_trylock().
*/
static int async_mutex_trylock(pthread_mutex_t *pMutex){
  int iIdx;
  int rc;
  pthread_mutex_t *aMutex = (pthread_mutex_t *)(&async);
  pthread_t *aHolder = (pthread_t *)(&asyncdebug);

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

  rc = pthread_mutex_trylock(pMutex);
  if( rc==0 ){
    assert(aHolder[iIdx]==0);
    aHolder[iIdx] = pthread_self();
  }
  return rc;
}

/*
** Wrapper around pthread_cond_wait().
*/
static int async_cond_wait(pthread_cond_t *pCond, pthread_mutex_t *pMutex){
  int iIdx;
  int rc;
  pthread_mutex_t *aMutex = (pthread_mutex_t *)(&async);
  pthread_t *aHolder = (pthread_t *)(&asyncdebug);

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

  assert(pthread_equal(aHolder[iIdx],pthread_self()));
  aHolder[iIdx] = 0;
  rc = pthread_cond_wait(pCond, pMutex);
  if( rc==0 ){
    aHolder[iIdx] = pthread_self();
  }
  return rc;
}

/* Call our async_XX wrappers instead of selected pthread_XX functions */
#define pthread_mutex_lock    async_mutex_lock
#define pthread_mutex_unlock  async_mutex_unlock
#define pthread_mutex_trylock async_mutex_trylock
#define pthread_cond_wait     async_cond_wait

#endif   /* !defined(NDEBUG) */

/*
** 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 */
  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 */
  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);
}

/*
** Increment async.nFile in a thread-safe manner.
*/
static void incrOpenFileCount(){
  /* We must hold the queue mutex in order to modify async.nFile */
  pthread_mutex_lock(&async.queueMutex);
  if( async.nFile==0 ){
    async.ioError = SQLITE_OK;
  }
  async.nFile++;
  pthread_mutex_unlock(&async.queueMutex);
}

/*
** 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, 
  i64 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 */
  pthread_mutex_lock(&async.lockMutex);
  p->lock.eLock = 0;
  pthread_mutex_unlock(&async.lockMutex);

  addAsyncWrite(&p->close);
  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, i64 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, i64 iOffset){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  i64 filesize;
  int nRead;
  sqlite3_file *pBase = p->pBaseRead;

  /* Grab the write queue mutex for the duration of the call */
  pthread_mutex_lock(&async.queueMutex);

  /* 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 = sqlite3OsFileSize(pBase, &filesize);
    if( rc!=SQLITE_OK ){
      goto asyncread_out;
    }
    nRead = MIN(filesize - iOffset, iAmt);
    if( nRead>0 ){
      rc = sqlite3OsRead(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->zName==zName ){
        int iBeginOut = (pWrite->iOffset-iOffset);
        int iBeginIn = -iBeginOut;
        int nCopy;

        if( iBeginIn<0 ) iBeginIn = 0;
        if( iBeginOut<0 ) iBeginOut = 0;
        nCopy = 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:
  pthread_mutex_unlock(&async.queueMutex);
  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, i64 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, i64 *piSize){
  AsyncFileData *p = ((AsyncFile *)pFile)->pData;
  int rc = SQLITE_OK;
  i64 s = 0;
  sqlite3_file *pBase;

  pthread_mutex_lock(&async.queueMutex);

  /* Read the filesystem size from the base file. If pBaseRead 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 = sqlite3OsFileSize(pBase, &s);
  }

  if( rc==SQLITE_OK ){
    AsyncWrite *pWrite;
    for(pWrite=async.pQueueFirst; pWrite; pWrite = pWrite->pNext){
      if( pWrite->op==ASYNC_DELETE && strcmp(p->zName, pWrite->zBuf)==0 ){
        s = 0;
      }else if( pWrite->pFileData && pWrite->pFileData->zName==p->zName){
        switch( pWrite->op ){
          case ASYNC_WRITE:
            s = MAX(pWrite->iOffset + (i64)(pWrite->nByte), s);
            break;
          case ASYNC_TRUNCATE:
            s = MIN(s, pWrite->iOffset);
            break;
        }
      }
    }
    *piSize = s;
  }
  pthread_mutex_unlock(&async.queueMutex);
  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 = sqlite3OsLock(pLock->pFile, eRequired);
      if( rc==SQLITE_OK ){
        pLock->eLock = eRequired;
      }
    }
    else if( eRequired<pLock->eLock && eRequired<=SQLITE_LOCK_SHARED ){
      rc = sqlite3OsUnlock(pLock->pFile, eRequired);
      if( rc==SQLITE_OK ){
        pLock->eLock = eRequired;
      }
    }
  }

  return rc;
}

/*
** The following two methods - asyncLock() and asyncUnlock() - are used
** to obtain and release locks on database files opened with the
** asynchronous backend.