Real Time Histogram Example

Suppose you have to read data from some resource and then to process the read bytes. But you don't want to block your main GUI's event loop during either operation. In this example I provide a simple solution provided the reading is fast enough to place it in the main thread and the processing is the slow enough to place it in another thread. Please, focus on the right version.

Structure

The goal is to divide the reading and processing into two threads. There are several ways to do this. I've done this right and wrong. See, for example, this great article.

Each version is a standalone project and contain it's own README.

The right version

This is the right way to use multithreading in Qt. It doesn't extends the QThread class. Instead it uses this class as a thread manager -- as it is supposed to be.

The wrong version

This is the wrong way to use multithreading in Qt. This comes from the wrong Qt documentation and based on extending the QThread class. Please, don't use this variant in your projects.

Requirements

• Qt 5 Qt 6
• Qwt (>= 6.2.0)
• cmake

Compilation and Run

Before you start you should specify the QWT_ROOT environment variable:

export QWT_ROOT=/path/to/Qwt

it stores the path to the root directory of the Qwt library on your system. In my case, for example (this line is in the .bashrc file):

export QWT_ROOT=/usr/local/qwt-6.2.0

After you've done with it, clone the repo:

git clone git@github.com:LRDPRDX/QwtRealTimeHistogram.git

And build an example (either wrong or right) :

cd QwtRealTimeHistogram/right
mkdir build
cd build

Generate Makefile and compile:

cmake ../
make

And run the example:

./real

NOTE: that I installed Qt 6 from source that is why I need CMAKE_PREFIX_PATH in my CMakeLists.txt. In your case you might not need it.