QThread::terminate() is documented to be thread-safe, but had a race
condition: If multiple threads call terminate() on the same thread,
the following could happen:
T1 T2
t0->terminate();
lock();
read ID;
pthread_cancel(ID);
unlock()
t0->terminate();
lock();
read ID;
(OS thread finishes)
t3->start();
(creates a new OS
thread with same ID)
pthread_cancel(ID); // cancels new t3!
unlock();
To fix, record that the thread was already terminated using a new
boolean flag.
An alternative would have been to fetchAndSet() the threadId to nullptr
and only let the thread that actually nulled it call pthread_cancel(),
but that would be harder to restore to the previous state in case
pthread_cancel() fails, and a null threadId might cause other problems
down the line, esp. if cancellation is currently disabled. The
explicit state is much simpler to reason about.
Fixes: QTBUG-127055
Pick-to: 6.7 6.5 6.2 5.15
Change-Id: Iec180bdfaaf913a3a1560210c781966dc99c0d42
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit d8bd4c2306f2acfefc75f8163b58f2037596dc65)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
4e26c36171