I need help with my Deno Qt/QML bindings - QGuiApplication::exec is blocking

nxctr

Hello,

I've been working on my QML bindings for Deno, the new JavaScript runtime. You can view them here: https://deno.land/x/qml@v0.1.5
But there are problems.

First off, some things you need to know.

Deno has a new (unstable) FFI API for calling native code.
Only C functions can be used. No C++ classes.
Buffers (aka strings) can be passed as input parameters, but they cannot be return values.
Because of this, the only way to make Qt work at this time is to declare a thread_local std::unique_ptr<App> global class and initialize QGuiApplication in an init() function.
FFI blocks the entire Deno event loop until the function returns.
It uses QGuiApplication and QQmlApplicationEngine.

The problem is that int exec() { return qGuiApp->exec(); } is blocking. I need to replace it with something like:

while (true) {
    processQtEvents();
    if (isDone()) break;
}

No matter how hard I tried, I can't figure out how to do it!

Things I've tried:

QEventLoop loop;
while (loop.isRunning()) {
    loop.processEvents(QEventLoop::AllEvents | QEventLoop::WaitForMoreEvents | QEventLoop::EventLoopExec);
}

while (true) {
    qGuiApp->processEvents(QEventLoop::AllEvents, 6000);
    if (qGuiApp->closingDown()) break;
}

qGuiApp->eventDispatcher()->processEvents(QEventLoop::AllEvents);

None of them work. The most common problem is that when the window is closed, the application still keeps running (aka the only way to end it is with CTRL+C). Signals such as QQmlApplicationEngine::quit and QQmlApplicationEngine::exit do not fire either.

I even tried making everything live in a global C++ thread class (not QThread) and passing data using mutexes and conditional variables, so that I could just have qGuiApp->exec() running in a separate thread and call isDone() from Deno. Still doesn't work. ThreadedApplication::operator()() and ThreadedApplication::setData() are in different threads, which Qt hates.

In simplest terms: can QGuiApplication::exec() be replaced with a while() loop?

I apologize if I'm not being clear about something. I'm at wits end to try and figure this out.

SGaist

Hi and welcome to devnet,

Did you try to integrate Qt's event loop with the one from Deno ?

AFAIK, QAbstractEventDispatcher is the starting for that.

nxctr

@SGaist Thanks for the reply. Unfortunately, Deno's event loop isn't exposed, at all. It's just calling functions from a C ABI using dlopen().