Category Archives: Platforms and frameworks

An alien civilization attack is starting with QT

QT is developed by an alien civilization that hate humans. They can’t make std::shared_ptr work in QML since 2014:

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QT signal performance significantly degrades when the number of the connections grow.

In my previous post I compared the performance of a single QT connection with the performance of a notification mechanism based on virtual functions.

In this post I’ll demonstrate how the performance of QT signals degrade when the number of the connections grow. Briefly saying a QT signal becomes 57 times slower than a virtual function.

Below I described my experimentations and provided the full source code.

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QT signal is ten times slower than a virtual function

I defined a QT Object that contains an integer value and uses QT signal along with awl::Observable based on virtual functions to notify the subscribers when the value changes:

#include "Awl/Observable.h"

#include <QObject>

namespace test
{
    class NotifyValueChanged
    {
    public:

        virtual void onValueChanged() = 0;
    };
    
    class ValueObject : 
        public QObject,
        public awl::Observable<NotifyValueChanged>
    {
        Q_OBJECT

    public:

        Q_PROPERTY(int value READ value WRITE setValue NOTIFY valueChanged)

        void notifyValueChanged()
        {
            Notify(&NotifyValueChanged::onValueChanged);
        }

    signals:

        void valueChanged();

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QObject::sender() is a slow function

I did not expect that its share of CPU usage in my app is 12.15%:

Why does it iterate over some collection? Isn’t there only one sender in a thread?

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Building QT 6.3.1 with OpenSSL for Windows

After various experimentation I was able to build QT 6.3.1 with OpenSSL for Windows with the following steps:

Extract archives with Bash:

tar -xzf ../distrib/openssl-1.1.1q.tar.gz
tar -xf ../distrib/qt-everywhere-src-6.3.1.tar.xz

Building OpenSSL 1.1.1q

Run the following commands with x64 Native Tools Command Prompt for VS 2022:

set PATH=%PATH%;C:\dev\PFiles\Strawberry\perl\bin
set PATH=%PATH%;C:\dev\PFiles\nasm-2.15.05
perl Configure VC-WIN64A
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Experimentation with OpenSSL and QT configuration on Windows

Building OpenSSL 1.1.1q with custom installation directory

Run the following commands with x64 Native Tools Command Prompt for VS 2022:

set PATH=%PATH%;C:\dev\PFiles\Strawberry\perl\bin
set PATH=%PATH%;C:\dev\PFiles\nasm-2.15.05
set MY_INSTALL_DIR=C:/dev/libs/OpenSSL
perl Configure VC-WIN64A --prefix="%MY_INSTALL_DIR%" --openssldir="%MY_INSTALL_DIR%"
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My experimentation with QML Repeater

I was able to define a Repeater that displays cryptocurrency market orders:

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Building QT 6.3.0 for Android on Windows with C++20

An example of how it can be configured:

set "CMAKE_ROOT=E:\PFiles\cmake-3.21.3-windows-x86_64\bin"
set "NINJA_ROOT=E:\PFiles\ninja-win"
set "JDK_ROOT=C:\Program Files\Java\jdk1.8.0_301\bin"
set "MINGW_ROOT=E:\PFiles\mingw-w64\x86_64-8.1.0-posix-seh-rt_v6-rev0\mingw64\bin"
set "PERL_ROOT=E:\PFiles\Strawberry\perl\bin"
       
set PATH=C:\WINDOWS\system32;C:\WINDOWS
set PATH=%CMAKE_ROOT%;%PATH%
set PATH=%NINJA_ROOT%;%PATH%
set PATH=%JDK_ROOT%;%PATH%
set PATH=%MINGW_ROOT%;%PATH%
set PATH=%PERL_ROOT%;%PATH%
set PATH=E:\PFiles\Python35;%PATH%
         
rem Check if the tools are in PATH
where gcc
where mingw32-make.exe
where perl.exe
where javac.exe
where python.exe
where cmake.exe
where ninja.exe
      
set "ANDROID_SDK_ROOT=C:\Users\D-Ef\AppData\Local\Android\Sdk"
set "ANDROID_NDK_PATH=C:\Users\D-Ef\AppData\Local\Android\Sdk\ndk\24.0.8215888"
set "ANDROID_BUILD_TOOLS_REVISION=31.0.0"
set "ANDROID_BUILD_ABI=x86_64"
rem set "ANDROID_BUILD_ABI=x86"
rem set "ANDROID_BUILD_ABI=arm64-v8a"
rem set "ANDROID_BUILD_ABI=armeabi-v7a"

set MY_INSTALL_PATH=E:/Qt/Qt6.3.0/android.%ANDROID_BUILD_ABI%
set QT_HOST_PATH=E:/Qt/Qt6.3.0/windows
      
configure.bat -platform win32-msvc -xplatform android-clang -prefix %MY_INSTALL_PATH% -qt-host-path %QT_HOST_PATH% ^
  -c++std c++20 -no-openssl ^
  -DQT_NO_EXCEPTIONS=1 -release -force-debug-info -opensource -confirm-license ^
  -android-sdk %ANDROID_SDK_ROOT% -android-ndk %ANDROID_NDK_PATH% -android-ndk-platform android-23 -android-abis %ANDROID_BUILD_ABI% ^
  -skip qt3d -skip qt5compat -skip qtactiveqt -skip qtcharts -skip qtcoap -skip qtconnectivity ^
  -skip qtdatavis3d -skip qtdoc -skip qtlottie -skip qtmqtt -skip qtnetworkauth -skip qtopcua ^
  -skip qtserialport -skip qtpositioning -skip qtquicktimeline -skip qtquick3d -skip qtremoteobjects ^
  -skip qtscxml -skip qtsensors -skip qtserialbus -skip qtvirtualkeyboard -skip qtwayland ^
  -skip qtwebchannel -skip qtwebengine -skip qtwebview
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Building QT 6.3.0 for Windows with OpenSSL and C++20

Now QT doesn’t like backslashes in configure.bat parameters. Also I updated vcvarsall.bat path and added -c++std c++20: and tried static build with -static option:

CALL "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\Auxiliary\Build\vcvarsall.bat" amd64
   
set "CMAKE_ROOT=E:\PFiles\cmake-3.21.3-windows-x86_64\bin"
set "NINJA_ROOT=E:\PFiles\ninja-win"
set "PERL_ROOT=E:\PFiles\Strawberry\perl\bin"
    
set PATH=%CMAKE_ROOT%;%PATH%
set PATH=%NINJA_ROOT%;%PATH%
set PATH=%PERL_ROOT%;%PATH%
set PATH=E:\PFiles\Python35;%PATH%
      
rem Check if the tools are in PATH
where perl.exe
where python.exe
where cmake.exe
where ninja.exe
  
set "MY_INSTALL_PATH=E:\Qt\Qt6.3.0\windows"
set CL=/MP
  
configure.bat -prefix %MY_INSTALL_PATH% -DQT_NO_EXCEPTIONS=1 -debug-and-release -force-debug-info -platform win32-msvc -opensource -confirm-license ^
-c++std c++20 -static -I "C:/Program Files/OpenSSL/include" -L "C:/Program Files/OpenSSL/lib"
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Dramatically annoying crash at std::thread and std::mutex destructors on Android

It is a long story that started here about 2 years ago. My first understanding was that it is a QT bug that was not fixed within this 2 years, of course (as a rule or usually), but a couple weeks ago I noticed that a similar crash happens on Samsung Galaxy devices:

#00  pc 000000000005fcb2  /apex/com.android.runtime/lib/bionic/libc.so (abort+166)
#00  pc 00000000000a9393  /apex/com.android.runtime/lib/bionic/libc.so (__fortify_fatal(char const*, ...)+26)
#00  pc 00000000000a8b9d  /apex/com.android.runtime/lib/bionic/libc.so (HandleUsingDestroyedMutex(pthread_mutex_t*, char const*)+20)
#00  pc 00000000000a8a89  /apex/com.android.runtime/lib/bionic/libc.so (pthread_mutex_lock+132)
#00  pc 00000000000a7879  /apex/com.android.runtime/lib/bionic/libc.so (pthread_cond_wait+40)
#00  pc 000000000004de2d  /system/lib/libc++.so (std::__1::condition_variable::wait(std::__1::unique_lock<std::__1::mutex>&)+8)
#00  pc 000000000038a7f1  /system/lib/libhwui.so (android::uirenderer::CommonPool::workerLoop()+60)
#00  pc 000000000038a73f  /system/lib/libhwui.so (void* std::__1::__thread_proxy<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct> >, android::uirenderer::CommonPool::CommonPool()::$_0> >(void*)+94)
#00  pc 00000000000a8147  /apex/com.android.runtime/lib/bionic/libc.so (__pthread_start(void*)+20)
#00  pc 0000000000061467  /apex/com.android.runtime/lib/bionic/libc.so (__start_thread+30)
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