Using std::future as a coroutine in C++20

In C++20 it is possible to do this:

std::future<int> compute(as_coroutine) {
  int a = co_await std::async([] { return 6; });
  int b = co_await std::async([] { return 7; });
  co_return a * b;
}
 
std::future<void> fail(as_coroutine) {
  throw std::runtime_error("bleah");
  co_return;
}
 
int main() {
  std::cout << compute({}).get() << '\n';
 
  try {
    fail({}).get();
  } catch (const std::runtime_error &e) {
    std::cout << "error: " << e.what() << '\n';
  }
}
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Switching to a different thread with async/await in C#

The code below switches to a different thread when the execution of Main() is resumed at line 11:

internal class Program
{
    static async Task Main(string[] args)
    {
        try
        {
            HttpClient client = new HttpClient();

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");
                
            HttpResponseMessage response = await client.GetAsync("https://developernote.com/");

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            response.EnsureSuccessStatusCode();

            string responseBody = await response.Content.ReadAsStringAsync();

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            Console.WriteLine(responseBody);
        }
        catch (HttpRequestException e)
        {
            Console.WriteLine("\nException Caught!");

            Console.WriteLine($"Thread: {Thread.CurrentThread.ManagedThreadId}");

            Console.WriteLine($"Message: {e.Message}");
        }
    }
}
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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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Testing Binance API with Postman

Clone the repository with Postman Collections and Environments:

git clone https://github.com/binance/binance-api-postman.git

Open the root repository folder:

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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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Building OpenSSL 3.0.2 with MSVC 2022

Download OpenSSL sources and extract them with Bash:

tar -xvzf /c/Users/D-Ef/Downloads/openssl-3.0.2.tar.gz

Download NASM, open x64 Native Tools Command Prompt for VS 2022 and run the following commands:

set PATH=%PATH%;E:\PFiles\nasm-2.15.05
where nasm
set PATH=%PATH%;E:\PFiles\Strawberry\perl\bin
where perl
set MY_INSTALL_DIR=E:\libs\OpenSSL
echo %MY_INSTALL_DIR%
perl Configure VC-WIN64A --prefix="%MY_INSTALL_DIR%" --openssldir="%MY_INSTALL_DIR%"
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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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Bold font in VS2022 C++ code editor

Visual Studio 2022 uses Cascadia Mono font by default:

They probably think that we all are infected by something and need to be vaccinated.

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Waitable QTimer with C++20 coroutines

Found an example of overriding co_await operator and was able to implement my own version:

#include <QTimer>
#include <QMetaObject>

#include <chrono>
#include <coroutine>

//QTimer accepts only milliseconds.
class TimeAwaitable
{
public:

    explicit TimeAwaitable(std::chrono::milliseconds d) : m_d(d) {}

    ~TimeAwaitable()
    {
        if (m_connection)
        {
            QObject::disconnect(m_connection);
        }
    }

    bool await_ready() const noexcept
    {
        return m_d <= std::chrono::milliseconds(0);
    }

    void await_suspend(std::coroutine_handle<> h) noexcept
    {
        m_connection = QObject::connect(&m_timer, &QTimer::timeout,
            [this, h]()
            {
                QObject::disconnect(m_connection);

                h.resume();
            });

        m_timer.setSingleShot(true);
        m_timer.start(m_d);
    }

    void await_resume() const noexcept {}

private:

    std::chrono::milliseconds m_d;
        
    QTimer m_timer;

    QMetaObject::Connection m_connection;
};

inline TimeAwaitable operator co_await(std::chrono::milliseconds d) noexcept
{
    return TimeAwaitable{ d };
}

For those who did not work with QT, QTimer::singleShot simply calls the lambda on the current thread after a given interval.

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