os_unix.c

这是一个开源的数据库系统,值得学习啊, 里面用了SQL语句,与微软的SQL SERVIER,差不了多少

      if (_AFPFSSetLock(context->filePath, pFile->h, RESERVED_BYTE, 1, 0)) {
        /* failed to release the reserved lock */
        rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
      }
    } 
  }
  if( locktype==NO_LOCK ){
    int failed = _AFPFSSetLock(context->filePath, pFile->h, 
                               SHARED_FIRST + context->sharedLockByte, 1, 0);
    if (failed) {
      rc = SQLITE_IOERR_UNLOCK;  /* This should never happen */
    }
  }
  if (rc == SQLITE_OK)
    pFile->locktype = locktype;
  leaveMutex();
  return rc;
}

/*
 ** Close a file & cleanup AFP specific locking context 
 */
static int afpUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)pId;

  if( !pFile ) return SQLITE_OK;
  afpUnixUnlock(*pId, NO_LOCK);
  /* free the AFP locking structure */
  if (pFile->lockingContext != NULL) {
    if (((afpLockingContext *)pFile->lockingContext)->filePath != NULL)
      sqlite3_free(((afpLockingContext*)pFile->lockingContext)->filePath);
    sqlite3_free(pFile->lockingContext);
  }

  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  close(pFile->h);
  pFile->isOpen = 0;
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  return SQLITE_OK;
}


#pragma mark flock() style locking

/*
 ** The flockLockingContext is not used
 */
typedef void flockLockingContext;

static int flockUnixCheckReservedLock(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if (pFile->locktype == RESERVED_LOCK) {
    return 1; /* already have a reserved lock */
  } else {
    /* attempt to get the lock */
    int rc = flock(pFile->h, LOCK_EX | LOCK_NB);
    if (!rc) {
      /* got the lock, unlock it */
      flock(pFile->h, LOCK_UN);
      return 0;  /* no one has it reserved */
    }
    return 1; /* someone else might have it reserved */
  }
}

static int flockUnixLock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  
  /* if we already have a lock, it is exclusive.  
  ** Just adjust level and punt on outta here. */
  if (pFile->locktype > NO_LOCK) {
    pFile->locktype = locktype;
    return SQLITE_OK;
  }
  
  /* grab an exclusive lock */
  int rc = flock(pFile->h, LOCK_EX | LOCK_NB);
  if (rc) {
    /* didn't get, must be busy */
    return SQLITE_BUSY;
  } else {
    /* got it, set the type and return ok */
    pFile->locktype = locktype;
    return SQLITE_OK;
  }
}

static int flockUnixUnlock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  
  assert( locktype<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->locktype==locktype ){
    return SQLITE_OK;
  }
  
  /* shared can just be set because we always have an exclusive */
  if (locktype==SHARED_LOCK) {
    pFile->locktype = locktype;
    return SQLITE_OK;
  }
  
  /* no, really, unlock. */
  int rc = flock(pFile->h, LOCK_UN);
  if (rc)
    return SQLITE_IOERR_UNLOCK;
  else {
    pFile->locktype = NO_LOCK;
    return SQLITE_OK;
  }
}

/*
 ** Close a file.
 */
static int flockUnixClose(sqlite3_file *pId) {
  unixFile *pFile = (unixFile*)*pId;
  
  if( !pFile ) return SQLITE_OK;
  flockUnixUnlock(*pId, NO_LOCK);
  
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();
  
  close(pFile->h);  
  leaveMutex();
  pFile->isOpen = 0;
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  return SQLITE_OK;
}

#pragma mark Old-School .lock file based locking

/*
 ** The dotlockLockingContext structure contains all dotlock (.lock) lock
 ** specific state
 */
typedef struct dotlockLockingContext dotlockLockingContext;
struct dotlockLockingContext {
  char *lockPath;
};


static int dotlockUnixCheckReservedLock(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 
    (dotlockLockingContext *) pFile->lockingContext;
  
  if (pFile->locktype == RESERVED_LOCK) {
    return 1; /* already have a reserved lock */
  } else {
    struct stat statBuf;
    if (lstat(context->lockPath,&statBuf) == 0)
      /* file exists, someone else has the lock */
      return 1;
    else
      /* file does not exist, we could have it if we want it */
      return 0;
  }
}

static int dotlockUnixLock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 
    (dotlockLockingContext *) pFile->lockingContext;
  
  /* if we already have a lock, it is exclusive.  
  ** Just adjust level and punt on outta here. */
  if (pFile->locktype > NO_LOCK) {
    pFile->locktype = locktype;
    
    /* Always update the timestamp on the old file */
    utimes(context->lockPath,NULL);
    return SQLITE_OK;
  }
  
  /* check to see if lock file already exists */
  struct stat statBuf;
  if (lstat(context->lockPath,&statBuf) == 0){
    return SQLITE_BUSY; /* it does, busy */
  }
  
  /* grab an exclusive lock */
  int fd = open(context->lockPath,O_RDONLY|O_CREAT|O_EXCL,0600);
  if (fd < 0) {
    /* failed to open/create the file, someone else may have stolen the lock */
    return SQLITE_BUSY; 
  }
  close(fd);
  
  /* got it, set the type and return ok */
  pFile->locktype = locktype;
  return SQLITE_OK;
}

static int dotlockUnixUnlock(sqlite3_file *id, int locktype) {
  unixFile *pFile = (unixFile*)id;
  dotlockLockingContext *context = 
    (dotlockLockingContext *) pFile->lockingContext;
  
  assert( locktype<=SHARED_LOCK );
  
  /* no-op if possible */
  if( pFile->locktype==locktype ){
    return SQLITE_OK;
  }
  
  /* shared can just be set because we always have an exclusive */
  if (locktype==SHARED_LOCK) {
    pFile->locktype = locktype;
    return SQLITE_OK;
  }
  
  /* no, really, unlock. */
  unlink(context->lockPath);
  pFile->locktype = NO_LOCK;
  return SQLITE_OK;
}

/*
 ** Close a file.
 */
static int dotlockUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if( !pFile ) return SQLITE_OK;
  dotlockUnixUnlock(*pId, NO_LOCK);
  /* free the dotlock locking structure */
  if (pFile->lockingContext != NULL) {
    if (((dotlockLockingContext *)pFile->lockingContext)->lockPath != NULL)
      sqlite3_free( ( (dotlockLockingContext *)
        pFile->lockingContext)->lockPath);
    sqlite3_free(pFile->lockingContext);
  }
  
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();
  
  close(pFile->h);
  
  leaveMutex();
  pFile->isOpen = 0;
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  return SQLITE_OK;
}


#pragma mark No locking

/*
 ** The nolockLockingContext is void
 */
typedef void nolockLockingContext;

static int nolockUnixCheckReservedLock(sqlite3_file *id) {
  return 0;
}

static int nolockUnixLock(sqlite3_file *id, int locktype) {
  return SQLITE_OK;
}

static int nolockUnixUnlock(sqlite3_file *id, int locktype) {
  return SQLITE_OK;
}

/*
 ** Close a file.
 */
static int nolockUnixClose(sqlite3_file *id) {
  unixFile *pFile = (unixFile*)id;
  
  if( !pFile ) return SQLITE_OK;
  if( pFile->dirfd>=0 ) close(pFile->dirfd);
  pFile->dirfd = -1;
  enterMutex();
  
  close(pFile->h);
  
  leaveMutex();
  pFile->isOpen = 0;
  OSTRACE2("CLOSE   %-3d\n", pFile->h);
  OpenCounter(-1);
  return SQLITE_OK;
}

#endif /* SQLITE_ENABLE_LOCKING_STYLE */


/*
** Information and control of an open file handle.
*/
static int unixFileControl(sqlite3_file *id, int op, void *pArg){
  switch( op ){
    case SQLITE_FCNTL_LOCKSTATE: {
      *(int*)pArg = ((unixFile*)id)->locktype;
      return SQLITE_OK;
    }
  }
  return SQLITE_ERROR;
}

/*
** Return the sector size in bytes of the underlying block device for
** the specified file. This is almost always 512 bytes, but may be
** larger for some devices.
**
** SQLite code assumes this function cannot fail. It also assumes that
** if two files are created in the same file-system directory (i.e.
** a database and it's journal file) that the sector size will be the
** same for both.
*/
static int unixSectorSize(sqlite3_file *id){
  return SQLITE_DEFAULT_SECTOR_SIZE;
}

/*
** Return the device characteristics for the file. This is always 0.
*/
static int unixDeviceCharacteristics(sqlite3_file *id){
  return 0;
}

/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix.
*/
static const sqlite3_io_methods sqlite3UnixIoMethod = {
  1,                        /* iVersion */
  unixClose,
  unixRead,
  unixWrite,
  unixTruncate,
  unixSync,
  unixFileSize,
  unixLock,
  unixUnlock,
  unixCheckReservedLock,
  unixFileControl,
  unixSectorSize,
  unixDeviceCharacteristics
};

#ifdef SQLITE_ENABLE_LOCKING_STYLE
/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix with AFP style file locking.
*/
static const sqlite3_io_methods sqlite3AFPLockingUnixIoMethod = {
  1,                        /* iVersion */
  unixClose,
  unixRead,
  unixWrite,
  unixTruncate,
  unixSync,
  unixFileSize,
  afpUnixLock,
  afpUnixUnlock,
  afpUnixCheckReservedLock,
  unixFileControl,
  unixSectorSize,
  unixDeviceCharacteristics
};

/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix with flock() style file locking.
*/
static const sqlite3_io_methods sqlite3FlockLockingUnixIoMethod = {
  1,                        /* iVersion */
  flockUnixClose,
  unixRead,
  unixWrite,
  unixTruncate,
  unixSync,
  unixFileSize,
  flockUnixLock,
  flockUnixUnlock,
  flockUnixCheckReservedLock,
  unixFileControl,
  unixSectorSize,
  unixDeviceCharacteristics
};

/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix with dotlock style file locking.
*/
static const sqlite3_io_methods sqlite3DotlockLockingUnixIoMethod = {
  1,                        /* iVersion */
  dotlockUnixClose,
  unixRead,
  unixWrite,
  unixTruncate,
  unixSync,
  unixFileSize,
  dotlockUnixLock,
  dotlockUnixUnlock,
  dotlockUnixCheckReservedLock,
  unixFileControl,
  unixSectorSize,
  unixDeviceCharacteristics
};

/*
** This vector defines all the methods that can operate on an sqlite3_file
** for unix with dotlock style file locking.
*/
static const sqlite3_io_methods sqlite3NolockLockingUnixIoMethod = {
  1,                        /* iVersion */
  nolockUnixClose,
  unixRead,
  unixWrite,
  unixTruncate,
  unixSync,
  unixFileSize,
  nolockUnixLock,
  nolockUnixUnlock,
  nolockUnixCheckReservedLock,
  un