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Cygwin: don't wait infinitely on a pthread cancel event 

Starting with commit 42faed4128 ("* thread.h (class pthread): Add bool
member canceled."), pthread::testcancel waits infinitely on cancel_event
after it checked if the canceled variable is set.  However, this might
introduce a deadlock, if the thread calling pthread_cancel is terminated
after setting canceled to true, but before calling SetEvent on cancel_event.

In fact, it's not at all necessary to wait infinitely.  By definition,
the thread is only canceled if cancel_event is set.  The canceled
variable is just a helper to speed up code.  We can safely assume that
the thread hasn't been canceled yet, if canceled is set, but cancel_event
isn't.

Fixes: 42faed4128 ("* thread.h (class pthread): Add bool member canceled.")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2023-07-17 18:02:04 +02:00
parent 816e9d67be
commit a02144808c
1 changed files with 3 additions and 6 deletions
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9
winsup/cygwin/thread.cc
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@ -962,12 +962,9 @@ pthread::testcancel ()
pthread_testcancel function a lot without adding the overhead of
an OS call. Only if the thread is marked as canceled, we wait for
cancel_event being really set, on the off-chance that pthread_cancel
gets interrupted before calling SetEvent. */
if (canceled)
{
WaitForSingleObject (cancel_event, INFINITE);
cancel_self ();
}
gets interrupted or terminated before calling SetEvent. */
if (canceled && IsEventSignalled (cancel_event))
cancel_self ();
}
/* Return cancel event handle if it exists *and* cancel is not disabled.