It looks like that API only works on the main thread (since it uses the DOM).
If you really need to call such APIs on a background thread there are various ways to proxy the work back to the main thread. See https://emscripten.org/docs/porting/pthreads.html#proxying. If the code in question is not a JS library (e.g. if its written in EM_JS or EM_ASM) you can use `MAIN_THREAD_EM_ASM` and/or `emscripten_sync_run_in_main_thread` helpers. cheers, sam On Thu, Oct 13, 2022 at 8:31 AM Balázs Varga <balazs.varga...@gmail.com> wrote: > Hi! > > I run into a problem with > QFileDialog::getOpenFileContent function, which are use to access to the > local filesystem with emscripten: > https://doc.qt.io/qt-5/qfiledialog.html#getOpenFileContent > > I tried to call it on a different thread then what on the wasm application > is running: > std::thread th1 (QFileDialog::getOpenFileContent, "*.*", onFileReady); > th1.join(); > > But in that case, it froze at the emscripten part in the openFileDialog > function and no file dialogue was opened. > emscripten::val document = emscripten::val::global("document"); > emscripten::val input = document.call<emscripten::val>("createElement", > std::string("input")); > > > *I got the error message at creating the input value.* > > *https://codereview.qt-project.org/c/qt/qtbase/+/250461/7/src/gui/platform/wasm/qwasmlocalfileaccess.cpp#129* > <https://codereview.qt-project.org/c/qt/qtbase/+/250461/7/src/gui/platform/wasm/qwasmlocalfileaccess.cpp#129> > > Running on the main thread there is no error and works fine. > Any idea what could be the problem/solution here? > I got this error message: > > worker.js onmessage() captured an uncaught exception: TypeError: Cannot > read properties of undefined (reading 'createElement') > self.onmessage @ soffice.worker.js:207 > soffice.worker.js:208 TypeError: Cannot read properties of undefined > (reading 'createElement') > at methodCaller_emscripten$$val_$std$$string$ (eval at new_ > (47933e67-c694-46fe-af70-91dc8b50859c:8694:27), <anonymous>:5:20) > at __emval_call_method (47933e67-c694-46fe-af70-91dc8b50859c:9267:14) > at emscripten::internal::MethodCaller<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char > const*, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > emscripten::internal::MethodCaller<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char > const*, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >&&) (val.h:278) > at emscripten::val emscripten::val::call<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >(char const*, std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> >&&) emscripten::val > emscripten::val::call<emscripten::val, std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > >(char const*, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >&&) const (val.h:498) > at QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void > (qstdweb::FileList const&)> > QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void > (qstdweb::FileList const&)> const&) (qwasmlocalfileaccess.cpp:131) > at QWasmLocalFileAccess::openFiles(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)> > const&, std::__2::function<char* (unsigned long long, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> > QWasmLocalFileAccess::openFiles(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)> > const&, std::__2::function<char* (unsigned long long, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&) > (qwasmlocalfileaccess.cpp:156) > at QWasmLocalFileAccess::openFile(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned > long long, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> > QWasmLocalFileAccess::openFile(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned > long long, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&) > (qwasmlocalfileaccess.cpp:169) > at QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > QFileDialog::getOpenFileContent(QString const&, std::__2::function<void > (QString const&, QByteArray const&)> const&)::$_2::operator()() > (qfiledialog.cpp:2444) > at decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString > const&, std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(fp)()) > std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(fp)()) > std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&) > (type_traits:3694) > at void std::__2::__invoke_void_return_wrapper<void, > true>::__call<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> void > std::__2::__invoke_void_return_wrapper<void, > true>::__call<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&) > (__functional_base:348)worker.js onmessage() captured an uncaught > exception: TypeError: Cannot read properties of undefined (reading > 'createElement') > self.onmessage @ soffice.worker.js:207 > soffice.worker.js:208 TypeError: Cannot read properties of undefined > (reading 'createElement') > at methodCaller_emscripten$$val_$std$$string$ (eval at new_ > (47933e67-c694-46fe-af70-91dc8b50859c:8694:27), <anonymous>:5:20) > at __emval_call_method (47933e67-c694-46fe-af70-91dc8b50859c:9267:14) > at emscripten::internal::MethodCaller<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char > const*, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > emscripten::internal::MethodCaller<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >::call(emscripten::internal::_EM_VAL*, char > const*, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >&&) (val.h:278) > at emscripten::val emscripten::val::call<emscripten::val, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> > >(char const*, std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> >&&) emscripten::val > emscripten::val::call<emscripten::val, std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > >(char const*, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >&&) const (val.h:498) > at QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void > (qstdweb::FileList const&)> > QWasmLocalFileAccess::openFileDialog(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void > (qstdweb::FileList const&)> const&) (qwasmlocalfileaccess.cpp:131) > at QWasmLocalFileAccess::openFiles(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)> > const&, std::__2::function<char* (unsigned long long, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> > QWasmLocalFileAccess::openFiles(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > QWasmLocalFileAccess::FileSelectMode, std::__2::function<void (int)> > const&, std::__2::function<char* (unsigned long long, > std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&) > (qwasmlocalfileaccess.cpp:156) > at QWasmLocalFileAccess::openFile(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned > long long, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> > QWasmLocalFileAccess::openFile(std::__2::basic_string<char, > std::__2::char_traits<char>, std::__2::allocator<char> > const&, > std::__2::function<void (bool)> const&, std::__2::function<char* (unsigned > long long, std::__2::basic_string<char, std::__2::char_traits<char>, > std::__2::allocator<char> >)> const&, std::__2::function<void ()> const&) > (qwasmlocalfileaccess.cpp:169) > at QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > QFileDialog::getOpenFileContent(QString const&, std::__2::function<void > (QString const&, QByteArray const&)> const&)::$_2::operator()() > (qfiledialog.cpp:2444) > at decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString > const&, std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(fp)()) > std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > decltype(std::__2::forward<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(fp)()) > std::__2::__invoke<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&) > (type_traits:3694) > at void std::__2::__invoke_void_return_wrapper<void, > true>::__call<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> void > std::__2::__invoke_void_return_wrapper<void, > true>::__call<QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> > const&)::$_2&>(QFileDialog::getOpenFileContent(QString const&, > std::__2::function<void (QString const&, QByteArray const&)> const&)::$_2&) > (__functional_base:348) > > Thanks in advance, > Balazs > > -- > You received this message because you are subscribed to the Google Groups > "emscripten-discuss" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to emscripten-discuss+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/emscripten-discuss/0b5c70fa-8cd2-4705-a64c-4816c1189dccn%40googlegroups.com > 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