Details
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Bug
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Resolution: Duplicate
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Not Evaluated
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None
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6.4.2
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None
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OS: Debian trixie/testing (latest)
Kernel: 6.5.0-2-amd64
DE: Xfce 4.18
WM: Xfwm4
CPU: AMD Ryzen 7 5800X (16) @ 3.800GHz
GPU: NVIDIA GeForce RTX 3070
Memory: 32012MiB
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Linux/X11
Description
The following code freezes the main/UI thread:
void MainWindow::on_pushButton_clicked() { QProgressDialog dlg(this); QVector<int> test; test.resize(1000); auto future = QtConcurrent::map(test, [](int& i) { QThread::msleep(1000); }); dlg.exec(); future.waitForFinished(); }
I would expect UI to be responsive while the worker threads are doing work (or sleeping in this example case). When the work finishes, the UI becomes responsive again. While it's not finished, the main/UI thread appears to be waiting to acquire some semaphore in drawing code:
#0 syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38 #1 0x00007ffff7468bb2 in QSemaphore::acquire(int) () at /lib/x86_64-linux-gnu/libQt6Core.so.6 #2 0x00007ffff691cf8e in () at /lib/x86_64-linux-gnu/libQt6Gui.so.6 #3 0x00007ffff66566ce in () at /lib/x86_64-linux-gnu/libQt6Gui.so.6 #4 0x00007ffff6634f14 in () at /lib/x86_64-linux-gnu/libQt6Gui.so.6 #5 0x00007ffff6657adc in QRasterPaintEngine::drawLines(QLine const*, int) () at /lib/x86_64-linux-gnu/libQt6Gui.so.6 ...
(Full stacktrace: stacktrace.txt
)
There is no problem with a small number of elements in the vector (up to 15). Also, QtConcurrent::run and QtConcurrent::task work fine.
The issue is not reproducible with Qt 5.15.10.