导入了用户以后，那么将会调用importusers_optimize()。最后，当该操作也完成后，那么将会调用我们在finished键中指定的回调（importusers_finished()）。下面是importusers_import()函数：
/**
* Batch callback operation: Import users.
*
* @param $size
* Number of users to import in each operation.
* @param $context
* Batch context containing state information.
*/
function importusers_import($size, &$context) {
// Initialize sandbox the first time through.
if (!isset($context['sandbox']['progress'])) {
$context['sandbox']['progress'] = 0;
$context['sandbox']['current_user_id'] = 0;
$context['sandbox']['max'] = db_result(
db_query('SELECT COUNT(DISTINCT user_id) FROM {old_users}'));
}
// Retrieve some users from the old_users table.
$result = db_query_range("SELECT user_id, username AS name, email AS mail,
pass FROM {old_users} WHERE user_id > %d ORDER BY user_id",
$context['sandbox']['current_user_id'], 0, $size);
// Transform them into Drupal users.
while ($account = db_fetch_array($result)) {
$new_user = user_save(array(), $account);
// Update progress information.
$context['sandbox']['progress']++;
$context['sandbox']['current_user_id'] = $account['user_id'];
$context['message'] = t('Importing user %username', array('%username' =>
$new_user->name));
// Store usernames in case the the 'finished' callback wants them.
$context['results'][] = $new_user->name;
}
// Let the batch engine know how close we are to completion.
if ($context['sandbox']['progress'] == $context['sandbox']['max']) {
// Done!
$context['finished'] = 1;
}
else {
$context['finished'] = $context['sandbox']['progress'] /
$context['sandbox']['max'];
}
}
/**
* Batch callback operation: Optimize users.
* For now, this function does nothing.
*
* @param $context
* Batch context containing state information.
*/
function importusers_optimize(&$context) {
// Code would go here.
// Inform the batch engine that we are done.
$context['finished'] = 1;
}
注意，除了你在批处理集操作数组中指出的参数以外，importusers_import()还接收了另一个名为$context的参数。$context是一个数组，它是通过引用传递的，它包含了来自于批处理引擎的关于当前批处理集的状态信息。$context的内容如下所示：
• sandbox:这个区域是供回调函数使用的。你可以在这里存储你需要的任何东西，并且它将会自动持久化。在我们的例子中，我们存储的信息有，要导入的用户数，当前正被导入的用户，等等。在批处理进行处理期间，使用这个来存储信息，而不是使用$_SESSION。如果你使用了$_SESSION，那么当用户打开了一个新的浏览器窗口，就可能出错。
• results:这个给finished回调使用的包含结果的数组。例如，如果用户想看到导入的用户名的列表时，那么就可以使用这个。
• message:是用来显示在进度页面的消息。
• finished:这是一个浮点数字，位于从0到1之间，用来指示处理了多少数据。当所有的数据处理完时，将它设置为1，来指示批处理引擎可以继续下一个操作了。
下面是所有的批处理操作运行完成以后，所要调用的回调：
/**
* Called when all batch operations are complete.
*/
function importusers_finished($success, $results, $operations) {
if ($success) {
drupal_set_message(t('User importation complete.'));
}
else {
// A fatal error occurred during batch processing.
$error_operation = reset($operations);
$operation = array_shift($error_operation);
$arguments = array_shift($error_operation);
$arguments_as_string = implode(', ', $arguments);
watchdog('importusers', "Error when calling operation '%s'('%s')",
array($operation, $arguments_as_string));
drupal_set_message(t('An error occurred and has been recorded
in the system log.'), 'error');
}
}