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Hello,</div>
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<br>
</div>
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I would like to report a deterministic QObject wrapper-invalidation</div>
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difference after a QApplication is destroyed and a new QApplication is</div>
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created later in the same Python process. Only one QApplication exists at</div>
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any time, and both are created on the main thread.</div>
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<br>
</div>
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Before treating this as a bug, I would also like to clarify whether</div>
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sequential QApplication lifetimes are supported by PyQt6.</div>
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<br>
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Summary</div>
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-------</div>
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<br>
</div>
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The attached small, complete PyQt-only script creates QSplitter objects,</div>
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retains the Python wrappers returned by QSplitter.handle(1), deletes each</div>
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owning splitter, and then observes the wrappers with PyQt6.sip.isdeleted().</div>
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<br>
</div>
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It compares two modes, each run in a fresh Python process:</div>
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<br>
</div>
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1. single: both epochs use the same QApplication.</div>
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2. recreate: the first QApplication is fully destroyed before a second</div>
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QApplication is constructed.</div>
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<br>
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Under a single QApplication, handle wrappers are invalidated in both</div>
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epochs. After recreating QApplication, all handle destroyed slots are still</div>
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called under the second application, and all owning splitter wrappers are</div>
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marked deleted, but none of the retained handle wrappers are marked deleted.</div>
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<br>
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Environment</div>
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-----------</div>
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<br>
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Primary current-version reproduction:</div>
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<br>
</div>
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- Windows 11 10.0.26200, 64-bit</div>
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- CPython 3.12.14, 64-bit</div>
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- PyQt6 6.11.0</div>
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- PyQt6-Qt6 6.11.2</div>
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- Qt compile-time version 6.11.0</div>
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- Qt runtime version 6.11.2</div>
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- PyQt6-sip 13.12.0</div>
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- Reproduced with QT_QPA_PLATFORM=offscreen and windows</div>
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<br>
</div>
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The same result was also observed with:</div>
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<br>
</div>
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- PyQt6 6.7.1</div>
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- Qt compile-time version 6.7.1</div>
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- Qt runtime version 6.7.3</div>
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- PyQt6-sip 13.8.0</div>
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<br>
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How to run</div>
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----------</div>
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<br>
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Run each command in a fresh process:</div>
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<br>
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py -3.12 minimal_repro.py single</div>
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py -3.12 minimal_repro.py recreate</div>
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<br>
</div>
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The script defaults to the offscreen QPA plugin. To use the Windows plugin:</div>
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<br>
</div>
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set QT_QPA_PLATFORM=windows</div>
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py -3.12 minimal_repro.py single</div>
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py -3.12 minimal_repro.py recreate</div>
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<br>
</div>
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Each command exits with status 0, writes JSON to stdout, and writes nothing</div>
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to stderr in my environment.</div>
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<br>
</div>
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Expected result</div>
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---------------</div>
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<br>
</div>
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If constructing a new QApplication after completely destroying the previous</div>
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one is supported, QObject wrapper lifetime tracking under the second</div>
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application should behave like it does under the first application.</div>
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<br>
</div>
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After the owning QSplitter is destroyed and the handle's destroyed signal is</div>
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emitted, the retained QSplitterHandle wrapper should report</div>
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sip.isdeleted(handle) == True.</div>
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<br>
</div>
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Actual result on PyQt6 6.11.0</div>
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----------------------------</div>
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<br>
</div>
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mode epoch splitter deleted handle deleted destroyed slot seen</div>
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single 0 16/16 16/16 16/16</div>
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single 1 16/16 16/16 16/16</div>
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recreate 0 16/16 16/16 16/16</div>
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recreate 1 16/16 0/16 16/16</div>
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<br>
</div>
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At the recreate boundary, before constructing the second application:</div>
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<br>
</div>
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- the weak reference to the first QApplication wrapper is dead; and</div>
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- QApplication.instance() is None.</div>
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<br>
</div>
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Immediately after construction, QApplication.instance() is the second</div>
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application.</div>
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<br>
</div>
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For PyQt6 6.11.0 with the offscreen plugin, I ran single mode in 12 fresh</div>
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processes and recreate mode in 12 fresh processes. All 24 runs produced the</div>
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same respective result and empty stderr. One additional fresh-process run of</div>
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each mode with the Windows QPA plugin produced the same result.</div>
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<br>
</div>
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An earlier PyQt6 6.7.1 matrix also compared no destroyed callback, a plain</div>
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Python callback, and the class-defined zero-argument slot used here. Each</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
single/recreate cell was run in 12 fresh processes. All recreated cells had</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
192/192 handles marked deleted under the first application and 0/192 under</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
the second, irrespective of callback type.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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Safety and observer design</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
--------------------------</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
The reproducer intentionally does not force a crash. After delivering</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
DeferredDelete, it calls no Qt method on the splitter or handle. It reads only</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
sip.isdeleted(), plus a Python Boolean changed by the destroyed slot.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
The destroyed receiver is a strongly retained QObject subclass with a</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
class-defined, zero-argument @pyqtSlot(). It receives no QObject argument and</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
does not access sender() or capture the handle.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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Source-level observation and hypothesis</div>
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---------------------------------------</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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This is a hypothesis based on source inspection, not a confirmed diagnosis</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
of the installed wheel's compiled control flow.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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I downloaded the PyQt6 6.11.0 sdist from PyPI. Its SHA-256 is:</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
45dd60aa69976de1918b5ced6b4e7b6a25abd2a919ecef5fd5826ecc76718889</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
In that source tree:</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- sip/QtWidgets/qapplication.sip calls pyqt6_cleanup_qobjects() from the</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
QApplication destructor.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- sip/QtCore/qcoreapplication.sip does the same from the QCoreApplication</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
destructor.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- qpy/QtCore/qpycore_public_api.cpp, around lines 75-80, sets</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
PyQtMonitor::enabled = false during that cleanup.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- qpy/QtCore/qpycore_event_handlers.cpp initializes enabled to true and only</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
installs monitoring for a newly wrapped C++ QObject while it is enabled.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- I did not find a path in qpy/ or sip/ that sets the flag back to true when</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
a later QApplication is constructed.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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This appears consistent with application destruction disabling monitoring</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
for C++-created QObject wrappers during the second application lifetime.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
However, I have not verified the wheel at native-symbol or machine-code level,</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
so I am presenting this only as a source-level hypothesis for confirmation.</div>
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<br>
</div>
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Impact and limitation</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
---------------------</div>
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<br>
</div>
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I found this while investigating a native Windows access violation in a</div>
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larger GUI test sequence. The attached reproducer demonstrates only the</div>
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deterministic wrapper-invalidation gap and deliberately stops short of using</div>
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a potentially stale wrapper.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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It does not identify the wrapper involved in that larger access violation or</div>
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the faulting native instruction. The access violation is therefore context,</div>
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not proof of the source-level hypothesis.</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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Questions</div>
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---------</div>
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<br>
</div>
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1. Does PyQt6 support completely destroying a QApplication and constructing</div>
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another one later in the same process?</div>
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2. If so, should PyQtMonitor be re-enabled or reset for the new application</div>
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lifetime?</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
3. If sequential application lifetimes are intentionally unsupported, is one</div>
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QApplication per process the required contract?</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
<br>
</div>
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Workaround</div>
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----------</div>
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<br>
</div>
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Keeping one QApplication alive for the entire process avoids the issue in my</div>
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tests. Tests that require an independent application lifetime can be run in a</div>
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separate subprocess.</div>
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<br>
</div>
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Attachments</div>
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-----------</div>
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<br>
</div>
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- minimal_repro.py</div>
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- single-pyqt6-6.11.0-final.json</div>
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- recreate-pyqt6-6.11.0-final.json</div>
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- single-pyqt6-6.11.0-windows-qpa-final.json</div>
<div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
- recreate-pyqt6-6.11.0-windows-qpa-final.json</div>
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- README.txt</div>
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- SHA256SUMS.txt</div>
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<br>
</div>
<div style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 11pt; color: rgb(0, 0, 0);">
Thank you.</div>
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