从多个线程使用QSqlQuery [英] Using QSqlQuery from multiple threads

问题描述

我有很多正在运行的C ++ 11线程，它们都需要在某个时间访问数据库.在主要方面，我会初始化数据库连接并打开数据库. Qt文档说查询不是线程安全的，因此在线程内部存在QSqlQuery之前，我将使用全局互斥锁.

I have a lot of C++11 threads running which all need database access at some time. In main I do initalize the database connection and open the database. Qt documentation says that queries are not threadsafe so I use a global mutex until a QSqlQuery exists inside a thread.

这行得通，但是否可以保证正常工作，或者我有时会遇到问题?

This works but is that guaranteed to work or do I run into problems at some time?

推荐答案

看看

只能在创建连接的线程中使用连接. 在线程之间移动连接或从中创建查询 不支持其他线程.

A connection can only be used from within the thread that created it. Moving connections between threads or creating queries from a different thread is not supported.

因此，您确实确实需要每个线程一个连接.我通过基于线程生成动态名称来解决了这个问题:

So you do indeed need one connection per thread. I solved this by generating dynamic names based on the thread:

auto name = "my_db_" + QString::number((quint64)QThread::currentThread(), 16);
if(QSqlDatabase::contains(name))
    return QSqlDatabase::database(name);
else {
    auto db = QSqlDatabase::addDatabase( "QSQLITE", name);
    // open the database, setup tables, etc.
    return db;
}

如果您使用不受Qt管理的线程，请使用 QThreadStorage 为每个线程生成名称:

In case you use threads not managed by Qt make use of QThreadStorage to generate names per thread:

// must be static, to be the same for all threads
static QThreadStorage<QString> storage;

QString name;
if(storage.hasLocalData())
    name = storage.localData();
else {
    //simple way to get a random name
    name = "my_db_" + QUuid::createUuid().toString();
    storage.setLocalData(name);
}

重要提示:Sqlite可能会或可能不会处理多线程.请参见 https://sqlite.org/threadsafe.html .据我所知，嵌入到Qt中的sqlite是线程安全的，这就是默认设置，我在源代码中找不到任何禁用它的标志.但是，如果您使用的是其他sqlite版本，请确保它确实支持线程.

Important: Sqlite may or may not be able to handle multithreading. See https://sqlite.org/threadsafe.html. As far as I know, the sqlite embedded into Qt is threadsafe, as thats the default, and I could not find any flags that disable it in the sourcecode. But If you are using a different sqlite version, make shure it does actually support threads.

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