How to Implement an Async Server with QDBus？

lkimuka

My current QDBus server interface is synchronous. If the interface takes a long time to process, it causes blocking. How can I modify the server-side implementation to make the calls asynchronous?

Thanks in advance.

lkimuka

@SGaist Thank you very much. I read https://doc.qt.io/qt-6/qdbusdeclaringslots.html#delayed-replies before asking this question, but that wasn't what I was looking for. The D-Bus adaptors in my project are automatically generated with CMake, and the behavior isn't correct when I directly use the extra QDBusMessage parameter at the end of the search() parameters.

And I figured out how to do it after a few tries. The nitty-gritty of solving the problem is using Q_EMIT to send an async completion signal to the client, with the results passed along at that point.

Here is a simple example to demonstrate the solution:

public slots:
    // Asynchronously search
    Q_NOREPLY void async_search(QString keywords) {
        ...

        // Pass the results and notify the client once the time-consuming logic is finished
        Q_EMIT asyncSearchCompleted("test result");
    }

Q_SIGNALS:
    void asyncSearchCompleted(const QString& result);

To handle the results on the client side, we connect the signal to a slot:

QDBusInterface *iface = ...;
connect(iface, SIGNAL(asyncSearchCompleted(QString)), this, SLOT(handleSearchResult(QString)));

public slots:
    void handleSearchResult(const QString &result) {
        qDebug() << "Received async search result:" << result;
    }

SGaist

Hi,

How did you implement your server ?

lkimuka

@SGaist Hello,

Here are the header and implementation files for my QDBus server:
https://github.com/dxnu/deepin-anything/blob/master/src/server/include/core/base_event_handler.h

https://github.com/dxnu/deepin-anything/blob/master/src/server/src/core/base_event_handler.cpp

The base_event_handler class is my QDBus server implementation. I want to make the search() interface asynchronous.

SGaist

I don't see any server in there. You are using the system's server.

As for your question, I think what you are looking for is https://doc.qt.io/qt-6/qdbusdeclaringslots.html#delayed-replies

lkimuka

@SGaist Thank you very much. I read https://doc.qt.io/qt-6/qdbusdeclaringslots.html#delayed-replies before asking this question, but that wasn't what I was looking for. The D-Bus adaptors in my project are automatically generated with CMake, and the behavior isn't correct when I directly use the extra QDBusMessage parameter at the end of the search() parameters.

And I figured out how to do it after a few tries. The nitty-gritty of solving the problem is using Q_EMIT to send an async completion signal to the client, with the results passed along at that point.

Here is a simple example to demonstrate the solution:

public slots:
    // Asynchronously search
    Q_NOREPLY void async_search(QString keywords) {
        ...

        // Pass the results and notify the client once the time-consuming logic is finished
        Q_EMIT asyncSearchCompleted("test result");
    }

Q_SIGNALS:
    void asyncSearchCompleted(const QString& result);

To handle the results on the client side, we connect the signal to a slot:

QDBusInterface *iface = ...;
connect(iface, SIGNAL(asyncSearchCompleted(QString)), this, SLOT(handleSearchResult(QString)));

public slots:
    void handleSearchResult(const QString &result) {
        qDebug() << "Received async search result:" << result;
    }