Hi again,
Another thing I'm looking into is the emerging support for JSPI in
browsers, Emscripten, and Qt. And I wonder whether, in my below
experiments, I'm holding anything fundamentally wrong (which might
easily be the case):
I have a minimal qmake-based project that just shows a window with a
button, and when the button gets clicked it opens a dialog:
$ cat dialog.pro
CONFIG += debug
HEADERS += window.h
QT += widgets
SOURCES += main.cc
$ cat window.h
#ifndef INCLUDED_window_h
#define INCLUDED_window_h
#include "QtWidgets/QPushButton"
#include "QtWidgets/QWidget"
class Window: public QWidget {
Q_OBJECT
public:
Window();
private slots:
void showDialog();
private:
QPushButton * button_;
};
#endif
$ cat main.cc
#include "QtWidgets/QApplication"
#include "QtWidgets/QDialog"
#include "QtWidgets/QPushButton"
#include "window.h"
Window::Window() {
button_ = new QPushButton("dialog", this);
connect(button_, SIGNAL(clicked()), this, SLOT(showDialog()));
}
void Window::showDialog() {
QDialog dialog(this);
dialog.exec();
}
int main(int argc, char ** argv) {
QApplication app(argc, argv);
Window window;
window.show();
return app.exec();
}
When building this for Wasm and running it in a browser, opening the
dialog would give the expected
Warning: exec() is not supported on Qt for WebAssembly in this configuration.
Please build with asyncify support, or use an asynchronous API like
QDialog::open()
Uncaught Please compile your program with async support in order to use
asynchronous operations like emscripten_sleep
But when I build recent Qt dev branch configured with
`-feature-wasm-jspi`, and add `QMAKE_LFLAGS += -sJSPI` to dialog.pro, my
understanding is that opening the dialog should then work. However, at
least when I build against recent emsdk 3.1.73, and run in recent Chrome
131 with JSPI enabled in <chrome://flags>, opening the dialog causes an
Uncaught RuntimeError: attempting to suspend without a WebAssembly.promising
export
Am I doing anything wrong?
(And a minor observation regarding the need to explicitly set
`QMAKE_LFLAGS += -sJSPI` as described at
<https://code.qt.io/cgit/qt/qtdoc.git/commit/?id=7516b4e74feb55a34c4d1409854ad291cafd7b3e>
"wasm: document asyncify JSPI": My naive understanding is that that
should no longer be necessary thanks to
<https://code.qt.io/cgit/qt/qtbase.git/commit/?id=7a21ba15ed0385878ba9bf9741b8df9b61ebe3cc>
"wasm: support enabling JSPI via QT_EMSCRIPTEN_ASYNCIFY=2", but only
actually works when configuring Qt with the old `-device-option
QT_EMSCRIPTEN_ASYNCIFY=2`, but not with the new `-feature-wasm-jspi`
alternative introduced in
<https://code.qt.io/cgit/qt/qtbase.git/commit/?id=92ad0f1f014909a792d157dca680fca5cff01605>
"wasm: add configure option for asyncify JSPI". The latter presumably
forgot to adapt mkspecs/common/wasm/wasm.conf?)
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