Details
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Bug
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Resolution: Unresolved
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P2: Important
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None
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6.7.0, 6.8.0
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None
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WebAssembly
Description
Calling QQuickWidget::setSource on the WebAssembly target can sometimes hang.
I suspect this may be due to it blocking on the main thread, as when setSource is called, it outputs:
"Blocking on the main thread is very dangerous, see https://emscripten.org/docs/porting/pthreads.html#blocking-on-the-main-browser-thread"
With the following stack trace:
warnOnce @ qml_block_main_thread.js:4039 _emscripten_check_blocking_allowed @ qml_block_main_thread.js:7870 $__pthread_cond_timedwait @ qml_block_main_thread.wasm:0x15f5436 $pthread_cond_wait @ qml_block_main_thread.wasm:0x15f5988 $QWaitConditionPrivate::wait(QDeadlineTimer) @ qml_block_main_thread.wasm:0x20e469 $QWaitCondition::wait(QMutex*, QDeadlineTimer) @ qml_block_main_thread.wasm:0x20e5fd $QQmlThread::internalCallMethodInThread(QQmlThread::Message*) @ qml_block_main_thread.wasm:0x5bc763 $QQmlTypeLoaderThread::loadWithCachedUnit(QQmlRefPointer<QQmlDataBlob> const&, QQmlPrivate::CachedQmlUnit const*) @ qml_block_main_thread.wasm:0x5cfe75 $void QQmlTypeLoader::doLoad<CachedLoader>(CachedLoader const&, QQmlDataBlob*, QQmlTypeLoader::Mode) @ qml_block_main_thread.wasm:0x5bf157 $QQmlTypeLoader::getType(QUrl const&, QQmlTypeLoader::Mode) @ qml_block_main_thread.wasm:0x5c8370 $QQmlComponentPrivate::loadUrl(QUrl const&, QQmlComponent::CompilationMode) @ qml_block_main_thread.wasm:0x4c5387 $QQmlComponent::QQmlComponent(QQmlEngine*, QUrl const&, QObject*) @ qml_block_main_thread.wasm:0x4c5043 $QQuickWidgetPrivate::execute() @ qml_block_main_thread.wasm:0xbb95ba $QQuickWidget::setSource(QUrl const&) @ qml_block_main_thread.wasm:0xbbb4d1 $MainWindow::MainWindow(QWidget*)
This occurs with multithreaded version of Qt 6.7.0 and 6.8.0.
Simple example program that should reproduce the error message is attached. (This simple example doesn't hang though.)