Google App Engine数据存储区中的多线程

如何使从数据存储区获取和设置属性的操作安全，线程安全？

当前，我有将任务放入队列中的代码，每个任务执行一个任务，然后更新一个名为numberOfTasks的属性，该属性的类型为int。它基本上会获取此属性的当前值并对其进行递增。

但是，随着任务在队列中执行，由于线程问题，最终值将变得不正确。有时，两个任务试图同时更新属性，因此有时增量未完成。

任何人都可以帮助正确完成此工作吗？

数据存储区属性获取器方法：

private String doGet(String rowId) throws EntityNotFoundException {
    Key egsKey = KeyFactory.createKey(DATASTORE_KIND, rowId);

    Entity egsEntity = datastore.get(egsKey);

    // schema changed from String to Text type. Transparently handle that here.
    Object propertyValue = egsEntity.getProperty(PROPERTY_KEY);

    if (propertyValue instanceof String) {
        return (String) propertyValue;
    }

    Text text = (Text) propertyValue;

    return text.getValue();
}

数据存储区属性的设置方法：

private void doPut(String rowId, List<String> list) {
    Entity entity = new Entity(DATASTORE_KIND, rowId);
    entity.setProperty(PROPERTY_KEY, list);

    datastore.put(entity);
}

设置方法和获取方法：

public synchronized int getPendingUsersForProcessing() {
    String pendingUsersForProcessingAsString = null;
    try {
        pendingUsersForProcessingAsString = doGet(PENDING_USERS_FOR_PROCESSING);
        return Integer.valueOf(pendingUsersForProcessingAsString);
    } catch (NumberFormatException e) {
        throw new IllegalStateException("The num of last batches processed in Datastore is not a number: "
                + pendingUsersForProcessingAsString);
    } catch (EntityNotFoundException e) {
        return DEFAULT_PENDING_USERS_FOR_PROCESSING;
    }
}

/** {@inheritDoc } */
@Override
public synchronized void setPendingUsersForProcessing(int pendingUsersForProcessing) {
    doPut(PENDING_USERS_FOR_PROCESSING, String.valueOf(pendingUsersForProcessing));
    LOG.info("Number of Pending Users For Processing is set to : " + pendingUsersForProcessing);
}

我尝试更新属性的代码：

int pendingUsers = appProperties.getPendingUsersForProcessing();
int requestUsers = request.getUserKeys().size();
appProperties.setPendingUsersForProcessing(pendingUsers + requestUsers);