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authorGiuseppe D'Angelo <giuseppe.dangelo@kdab.com>2021-10-14 15:30:48 +0200
committerGiuseppe D'Angelo <giuseppe.dangelo@kdab.com>2021-12-07 16:56:49 +0100
commit84fba93ebb65077248201ff4ebcc3ce5c36f36c2 (patch)
tree43e5887caf6a4e988c73456d3c566870db22bea4 /src/plugins/sqldrivers/odbc/.prev_CMakeLists.txt
parentf898128ee2433201025df4ae07f73e8109376d32 (diff)
QThread::create(): request interruption and join on destructionHEADdev
If one destroys a running QThread, so far the behavior has been to crash (à la std::thread) -- assuming the thread hasn't already signalled that it has finished. This behavior is hostile to solutions such as using QThread::create(), which always require a wait() before destroying the thread object. We can use the opportunity to change the behavior without breaking any valid code. Instead of crashing, inside QThread's destructor we can ask the new thread to quit, and then join it (à la std::jthread). This simplifies the implementation of long-living runnables and the code that manages them. Deploying this solution for the whole QThread class may not be entirely painless. While no correct code would work differently with the proposed changes, incorrect code that deletes a running thread would no longer crash "loudly" -- instead, it might deadlock "quietly", have memory corruptions, etc. Hence I'm limiting this approach to only the threads created by QThread::create(), at least for the time being. This also side-steps perhaps the biggest problem of generalizing the approach, which is that placing such interrupt+join logic into~QThread's destructor would cause it to be run _after_ a QThread subclass' own destructor has run, destroying the subclass' data members too early. This might create an antipattern if one chooses to subclass QThread. With create(), a subclass in question exists, and it indeed has NSDMs, but it's entirely under our control (in fact, I'm placing the logic just in its dtor). [ChangeLog][QtCore][QThread] Destroying a QThread object created by QThread::create() while the thread that it manages is still running will now automatically ask that thread to quit, and will wait until the thread has finished. Before, this resulted in a program crash. See the documentation of QThread::~QThread() for more details. Change-Id: Ib268b13da422e277ee3ed6f6c7b2ecc8cea5750c Reviewed-by: Marc Mutz <marc.mutz@qt.io> Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
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