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  1. Qt
  2. QTBUG-126593

QQuickWidget::setSource blocks on main thread

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    • WebAssembly
    • 803f2562032f1a7ea3db3ab85b7860e9c66ad6ad

    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.)

       

       

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          relates to

          Task - A task that needs to be done. QTBUG-129071 wasm: fix multithreaded QmlTypeLoader deadlock

          • P2: Important - Urgent, should be fixed, but will not stop the release.
          • Closed
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              piwierci Piotr Wierciński
              srcejon Jon Beniston
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                Created:
                Updated:
                Resolved:

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