UDP data + circular buffer

Chanchan

Hey there !
I would like to receive UDP data and then put them in a circular buffer. I'm on it since monday and I dont know how to code it .... I dont found an example where both of the circular buffer and UDP reception exists... Actually I did a source code socket but that's all
Do you have like an example or something ? :)
Thanks !

jsulm

@Chanchan What exactly are your problems?
Did you read https://doc.qt.io/qt-5/qudpsocket.html?
There are links to examples as well.

Chanchan

@jsulm I already did an UDP socket, here is my code :

#include "myudp.h"

MyUDP::MyUDP(QObject *parent) :
    QObject(parent)
{
    // create a QUDP socket
    socket = new QUdpSocket(this);


    // The most common way to use QUdpSocket class is
    // to bind to an address and port using bind()
    // bool QAbstractSocket::bind(const QHostAddress & address,
    //     quint16 port = 0, BindMode mode = DefaultForPlatform)
    socket->bind(QHostAddress("192.168.2.x"), 14500);

    connect(socket, SIGNAL(readyRead()), this, SLOT(readyRead()));
}

void MyUDP::HelloUDP()
{
    QByteArray Data;
    Data.append("En ecoute");

    // Sends the datagram datagram
    // to the host address and at port.
    // qint64 QUdpSocket::writeDatagram(const QByteArray & datagram,
    //                      const QHostAddress & host, quint16 port)
    socket->writeDatagram(Data, QHostAddress("192.168.2.x"), 14500);
}

void MyUDP::readyRead()
{
    // when data comes in
    const auto SIZE_BUF = 500000; 
    QByteArray buffer;
    buffer.reserve(SIZE_BUF);
    buffer.resize(socket->pendingDatagramSize());

    QHostAddress sender;
    quint16 senderPort;

    // qint64 QUdpSocket::readDatagram(char * data, qint64 maxSize,
    //                 QHostAddress * address = 0, quint16 * port = 0)
    // Receives a datagram no larger than maxSize bytes and stores it in data.
    // The sender's host address and port is stored in *address and *port
    // (unless the pointers are 0).

    socket->readDatagram(buffer.data(), buffer.size(),&sender, &senderPort);

    qDebug() << "Message from: " << sender.toString();
    qDebug() << "Message port: " << senderPort;
    qDebug() << "Message: " << buffer;
}

But instead of use a "classic" buffer, I would integrate a Circular Buffer.
How Should I do that ?

jsulm

@Chanchan You will need to implement the circular buffer by yourself or find existing one. As far as I know Qt does not have such a container.

J.Hilk

@jsulm actually, I quick google search resulted in this surprise class

https://doc.qt.io/archives/qt-5.5/qt3d-qcircularbuffer.html#details

it's part of qt3d, which would explain, why I haven't heard of it before.

jsulm

@J.Hilk Yes, I saw it.
But I'm not sure why it is part of Qt3D module?! And is it still there in recent versions?

Chanchan

@J.Hilk
Yes I saw this page, I tried to implement it to my example but I didn't succeed :/

J.Hilk

@jsulm said in UDP data + circular buffer:

And is it still there in recent versions

that's a god point, I can't find it in the 5.12 docs. Therefore I don't think so ?

Anyway a basic circular buff is like 40 lines. One should be able to do create on fairly easily with based on e.g. QVector.

Chanchan

Ok, I will try found it and integrate to my code
I have another problem but I prefer to open another thread for it ^^
Thank you :)

Kent-Dorfman

Ring buffers are only applicable in specialized situations where you need a container of constant memory footprint and quick deque access of elements (such as hardware device I/O. I can see such a thing being in the 3d graphics modules, but its utility in the general framework is very limited. The buffering of incoming UDP is such a case where its utility is valid. There are many online references describing how to implement the ring buffer container.

EDIT: a gotcha that the op needs to be aware of is that you CANNOT create a ring buffer of n characters and expect to access sequences of those characters. each element must be explicitly accessed as a single operation. The reason is that when the head/tail loops back to element n[0] the sequence of characters is no longer contiguous.

aha_1980

@Chanchan and @J-Hilk: I might be wrong, but isn't QQueue exactly what you want?

aha_1980

@jsulm said in UDP data + circular buffer:

@Chanchan You will need to implement the circular buffer by yourself or find existing one. As far as I know Qt does not have such a container.

As said above, there is QQueue.

J.Hilk

@aha_1980 It's probably a better starting point, but the QQueue is not limited in size -> No circular buffer, right?

aha_1980

@J.Hilk said in UDP data + circular buffer:

QQueue is not limited in size

Correct. If you need this behavior, you have to check size() before enqueue().

Chanchan

Actually my case is :
I receive a lot of UDP data, I have to implement a process function to transfert these data to the good function, this function will implement datas, etc...
For this I need a circular buffer, I will take a look on your tips, thank you :)