Posts about technology and arts.

Fixing Qt warning "QLayout: Attempting to add QLayout "" to QWidget "", which already has a layout"

If you ever started Krita 3.x in your command line, and had a look at the console output, you may noticed the following warning.

QLayout: Attempting to add QLayout “” to QWidget “”, which already has a layout

Krita recently announced the release of 3.1.3-alpha-2, and while testing I saw this warning and decided to investigate why this warning happens.

There was already a similar question posted on StackOverflow. And the best answer’s initial paragraph gave me a hint of what to look for.

When you assign a widget as the parent of a QLayout by passing it into the constructor, the layout is automatically set as the layout for that widget. In your code you are not only doing this, but explicitly calling setlayout(). This is no problem when when the widget passed is the same. If they are different you will get an error because Qt tries to assign the second layout to your widget which has already had a layout set.

So, somewhere in Krita code, there was a a QWidget being created, and layouts were being added to it more than once. To find where the issue was happening was quite easy. A breakpoint at where the application is initialized, then step through a few times, until the message appeared in the console.

Further investigation led me to the History docker (the one that shows undo steps) constructor.

    QVBoxLayout *vl = new QVBoxLayout(page); // layout being set to page
    m_undoView = new KisUndoView(this);
    QHBoxLayout *hl = new QHBoxLayout(page); // layout being set to page again
    hl->addSpacerItem(new QSpacerItem(10, 1,  QSizePolicy::Expanding, QSizePolicy::Fixed));
    m_bnConfigure = new QToolButton(page);
    connect(m_bnConfigure, SIGNAL(clicked(bool)), SLOT(configure()));

    setWindowTitle(i18n("Undo History"));

Here the QWidget created receives both QHBoxLayout and QVBoxLayout. Again, searching the Internet a little bit, then came across this post with a good example of a QWidget with QHBoxLayout and QVBoxLayout. Here’s what the constructor looks after the patch has been applied.

    QVBoxLayout *vl = new QVBoxLayout(page); // layout being set to page
    m_undoView = new KisUndoView(this);
    QHBoxLayout *hl = new QHBoxLayout();
    hl->addSpacerItem(new QSpacerItem(10, 1,  QSizePolicy::Expanding, QSizePolicy::Fixed));
    m_bnConfigure = new QToolButton(page);
    connect(m_bnConfigure, SIGNAL(clicked(bool)), SLOT(configure()));
    vl->addLayout(hl); // horizontal layout added to the vertical layout

    setWindowTitle(i18n("Undo History"));

That’s it. Learned something new in Qt. Not as important and useful as learning about signals and slots, but now I can focus on other warnings in the console output of Krita.

And you? Have you tested Krita 3.1.3 alpha already? What are you waiting for? :-)

♥ Open Source

Simulating less memory with ulimit

These days I was trying to reproduce a bug in Krita where it would crash when a user copied group layers between windows. It appeared that the user was getting a segmentation fault due to the user’s computer running out of memory.

I could not reproduce the issue, but my computer has 16 GB. The first thing that came to my mind was to create a virtual machine with less memory to reproduce the issue. But I decided to spend some time looking for a simpler way of doing it.

Searching the web I found some suggestions that ulimit could work. After playing for a while with ulimit and htop, and verifying the amount of memory necessary to open two files in two windows in Krita, I came up with the following settings.

# 2550 mb in kb
ulimit -v 2550000

# 2 gb in kb
ulimit -m 2000000

# Confirm limits
ulimit -a

gdb $HOME/Development/cpp/workspace/krita_install/bin/krita

Then after copying a few layers from one window to another, I successfully reproduced the issue, and could include a backtrace in the Krita issue tracking system.

♥ Open Source

Using Google Natural Language API in an AWS Elastic Beanstalk application

Besides providing an API for users and developers, Google also provides a series of (very well-written) client implementation, in several programming languages. That’s the case for Google Storage, Google Vision, and for Google Natural Language API’s.

I recently had to use the latter in a POC at work, and ran into an interesting issue with our AWS Elastic Beanstalk environment.

Google Language API requires that clients authenticate before sending requests. If you use their google-cloud-java, you can define the GOOGLE_APPLICATION_CREDENTIALS. This environment variable must point to a JSON file with the Google Language API credentials.

The issue is that while Google Language API (or more precisely google-auth-library-java) looks for an environment variable, in Elastic Beanstalk you are able to specify only system properties (unless you want to try something with ebextensions, maybe some JNI…).

A workaround for this issue in Google Natural Language API, is to create and pass a LanguageServiceSettings to your LanguageServiceClient. This settings object, when created, must be given a channel provider with a FixedCredentialsProvider.

Of course reading code is way easier than reading this workaround description.

// File:
// ...
    // envvar or property used to specify the Google Application Credentials

     * Google Natural Language API.
    private LanguageServiceClient languageServiceClient;

    public void init() throws Exception {
        // Elastic Beanstalk supports Properties, not Environment Variables.
        // Google credentials library will load
        // the JSON location for the service to authenticate from an envVar. So
        // we need to fix that here.
        String googleApplicationCredentials = System.getenv(GOOGLE_APPLICATION_CREDENTIALS);"GOOGLE_APPLICATION_CREDENTIALS in environment variable: %s", googleApplicationCredentials));
        if (StringUtils.isBlank(googleApplicationCredentials)) {
            googleApplicationCredentials = System.getProperty(GOOGLE_APPLICATION_CREDENTIALS);
  "GOOGLE_APPLICATION_CREDENTIALS in JVM property: %s", googleApplicationCredentials));

        if (googleApplicationCredentials == null) {
            throw new RuntimeException("Could not locate GOOGLE_APPLICATION_CREDENTIALS variable!");

        final LanguageServiceSettings languageServiceSettings;
        try (InputStream is = new FileInputStream(new File(googleApplicationCredentials))) {
            final GoogleCredentials myCredentials = GoogleCredentials
            final CredentialsProvider credentialsProvider = FixedCredentialsProvider.create(myCredentials);

            final InstantiatingChannelProvider channelProvider = LanguageServiceSettings
            languageServiceSettings = LanguageServiceSettings
        } catch (IOException ioe) {
            LOGGER.error(String.format("IO error creating Google NLP settings: %s", ioe.getMessage()), ioe);
            throw ioe;

        // Create Google API client
        this.languageServiceClient = LanguageServiceClient.create(languageServiceSettings);

    public void destroy() throws Exception {
        if (LOGGER.isDebugEnabled()) {
            LOGGER.debug("Destroying Google NLP API client");
        // Close Google API executors and channels
// ...

That way you should be able to use the API with AWS Elastic Beanstalk without having to hack your environment to provide the GOOGLE_APPLICATION_CREDENTIALS environment variable.

An alternative would be google-auth-library-java to look for an environment variable and a system property. Or maybe Amazon AWS add a way to provide environment variables.

Note also that I included the @PostConstruct and @PreDestroy annotated methods. The API will start an executor thread pool, so if you do not want to risk to have problems re-deploying your application, then remember to close your streams.

♥ Open Source

Order of containers in Docker Compose

In Docker Compose you are able to control the startup order of the containers via the depends_on statement. This is documented in Controlling startup order in Compose.

If you have a simple setup, with Tomcat and Postgres, sometimes Postgres will start first, but Compose will initialize Tomcat before Postgres has fully booted. When that happens, you may receive 401, 404, or other application errors.

You can fix it by combining depends_on with a healthcheck. For example:

# File: docker-compose.yml
version: '2.1'
    container_name: twpg
      context: .
      dockerfile: Dockerfile.postgres
    restart: always
      - "5432:5432"
      test: "pg_isready -h localhost -p 5432 -q -U postgres"
      interval: 10s
      timeout: 5s
      retries: 5

    container_name: twtc
      context: .
      dockerfile: Dockerfile.tomcat
    restart: always
        condition: service_healthy
      - db
      - "80:8080"

In the example docker-compose.yml, there are two containers, db and web. web is running a Tomcat, and db is running Postgres. Web depends on db (see depends_on), and uses a condition service_healthy. Which indicates it depends that that container is healthy.

The healthcheck entry under the db container settings define how to check whether Postgres is running or not. In this case, we are using pg_isready, which is available in the vanilla Postgres 9 container.

It will try 5 times, with a 10 seconds interval, and will time out after 5 seconds. You may have to tune these parameters for your application.

This code snippet is from a pull request submitted to Foxoncz/docker-thingworx.

♥ Open Source

Using AWS MFA without a mobile phone

If you use AWS, the chances are that you use MFA - Multi-factor Authentication - to authenticate. I don’t like to install apps in my mobile phone, unless I need to, so having bought a new phone recently, I decided to find a replacement for Google Authenticator.

There are several command line utilities, browser extensions, libraries, and tools (free and paid) that implement the TOTP - time-based one-time password -, the standard required by Amazon for MFA authentication.

I decided to use a Go tool for the first time: gauth. Note that you won’t be able to use it from home, in case you don’t bring your laptop home. You can have one MFA device linked to your AWS account, so you may have to remove an existing one. Follow these instructions with care :^)

Install Go

sudo apt update && sudo apt upgrade -y
cd tmp/ && wget
tar -zxvf go1.*.tar.gz
sudo mv go /usr/local
vim ~/.bashrc

Add the following at the bottom of the file.


And you can test it with . ~/.bashrc && go version.

Install gauth

Given your environment is correctly set up, you should be able to use the following command to install gauth, and have it available in your $PATH.

go get

Edit ~/.config/gauth.csv adding a value for the AWS MFA key.

Getting the AWS MFA key

To get the value that you must place in your gauth.csv file, you must add a new MFA device. When asked to scan a QR code, look for an option to enter the manual value. That will give you a long string. That’s the value you are looking for.

Extra: Auto copy-paste from command line

If you would like to quickly copy and paste, try creating an alias as described on this gist.

I used these instructions, and can now run one command line, that will put the next MFA code in my clipboard. Then just paste into my browser, and that’s that!

Happy hacking!