From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: Jon Turney <jon.turney@dronecode.org.uk>
Cc: cygwin-patches@cygwin.com
Subject: Re: [PATCH 08/11] Cygwin: testsuite: Busy-wait in cancel3 and cancel5
Date: Mon, 17 Jul 2023 13:05:08 +0200 [thread overview]
Message-ID: <ZLUgZE5ECv+HaAGI@calimero.vinschen.de> (raw)
In-Reply-To: <ZLGaf8/nWphfbRI9@calimero.vinschen.de>
On Jul 14 20:57, Corinna Vinschen wrote:
> On Jul 14 14:04, Jon Turney wrote:
> > On 13/07/2023 19:53, Corinna Vinschen wrote:
> > > > > Nevertheless, I think this is ok to do. The description of pthread_cancel
> > > > > contains this:
> > > > >
> > > > > Asynchronous cancelability means that the thread can be canceled at
> > > > > any time (usually immediately, but the system does not guarantee this).
> > > > >
> > > > > And
> > > > >
> > > > > The above steps happen asynchronously with respect to the
> > > > > pthread_cancel() call; the return status of pthread_cancel() merely
> > > > > informs the caller whether the cancellation request was successfully
> > > > > queued.
> > > > >
> > > > > So any assumption *when* the cancallation takes place is may be wrong.
> >
> > Yeah.
> >
> > I think the flakiness is when we happen to try to async cancel while in the
> > Windows kernel, which implicitly converts to a deferred cancellation, but
> > there are no cancellation points in the the thread, so it arrives at
> > pthread_exit() and returns a exit code other than PTHREAD_CANCELED.
>
> In pthread_join(), right?
>
> > I did consider making the test non-flaky by adding a final call to
> > pthread_testcancel(), to notice any failed async cancellation which has been
> > converted to a deferred one.
> >
> > But then that is just the same as the deferred cancellation tests, and
> > confirms the cancellation happens, but not that it's async, which is part of
> > the point of the test.
>
> What if Cygwin checks for a deferred cancellation in pthread::exit,
> too? It needs to do this by its own, not calling pthread::testcancel,
> otherwise we're in an infinite loop. Since cancel is basically like
> exit, just with a PTHREAD_CANCELED return value, the only additional
> action would be to set retval to PTHREAD_CANCELED explicitely.
Kind of like this:
diff --git a/winsup/cygwin/thread.cc b/winsup/cygwin/thread.cc
index f614e01c42f6..fceb9bda1806 100644
--- a/winsup/cygwin/thread.cc
+++ b/winsup/cygwin/thread.cc
@@ -546,6 +546,13 @@ pthread::exit (void *value_ptr)
class pthread *thread = this;
_cygtls *tls = cygtls; /* Save cygtls before deleting this. */
+ /* Deferred cancellation still pending? */
+ if (canceled)
+ {
+ WaitForSingleObject (cancel_event, INFINITE);
+ value_ptr = PTHREAD_CANCELED;
+ }
+
// run cleanup handlers
pop_all_cleanup_handlers ();
What do you think?
Corinna
next prev parent reply other threads:[~2023-07-17 11:05 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-13 11:38 [PATCH 00/11] More testsuite fixes Jon Turney
2023-07-13 11:38 ` [PATCH 01/11] Cygwin: testsuite: Setup test prereqs in 'installation' the tests run in Jon Turney
2023-07-13 11:38 ` [PATCH 02/11] Cygwin: testsuite: Add a simple timeout mechanism Jon Turney
2023-07-13 11:38 ` [PATCH 03/11] Cygwin: testsuite: Remove const from writable string in fcntl07b Jon Turney
2023-07-13 11:38 ` [PATCH 04/11] Cygwin: testsuite: Skip devdsp test when no audio devices present Jon Turney
2023-07-13 11:38 ` [PATCH 05/11] Cygwin: testsuite: Just log result of second open of /dev/dsp Jon Turney
2023-07-13 11:38 ` [PATCH 06/11] Cygwin: testsuite: Also check direct call in systemcall Jon Turney
2023-07-13 11:39 ` [PATCH 07/11] Cygwin: testsuite: Fix for limited thread priority values Jon Turney
2023-07-13 11:39 ` [PATCH 08/11] Cygwin: testsuite: Busy-wait in cancel3 and cancel5 Jon Turney
2023-07-13 11:43 ` Jon Turney
2023-07-13 18:16 ` Corinna Vinschen
2023-07-13 18:37 ` Corinna Vinschen
2023-07-13 18:53 ` Corinna Vinschen
2023-07-14 13:04 ` Jon Turney
2023-07-14 18:57 ` Corinna Vinschen
2023-07-17 11:05 ` Corinna Vinschen [this message]
2023-07-17 11:51 ` Jon Turney
2023-07-17 14:21 ` Corinna Vinschen
2023-07-17 15:41 ` Corinna Vinschen
2023-07-17 18:23 ` Corinna Vinschen
2023-07-18 11:20 ` Jon Turney
2023-07-18 12:09 ` Corinna Vinschen
2023-07-18 15:52 ` Jon Turney
2023-07-17 11:51 ` Jon Turney
2023-07-17 14:04 ` Corinna Vinschen
2023-07-17 14:22 ` Corinna Vinschen
2023-07-13 11:39 ` [PATCH 09/11] Cygwin: testsuite: Fix a buffer overflow in symlink01 Jon Turney
2023-07-13 18:17 ` Corinna Vinschen
2023-07-14 13:04 ` Jon Turney
2023-07-13 11:39 ` [PATCH 10/11] Cygwin: testsuite: Minor fixes to umask03 Jon Turney
2023-07-13 18:18 ` Corinna Vinschen
2023-07-13 11:39 ` [PATCH 11/11] Cygwin: testsuite: Drop Adminstrator privileges while running tests Jon Turney
2023-07-13 18:05 ` [PATCH 00/11] More testsuite fixes Corinna Vinschen
2023-07-17 11:58 ` Jon Turney
2023-07-17 14:02 ` Corinna Vinschen
2023-07-18 13:37 ` Jon Turney
2023-07-18 14:52 ` Corinna Vinschen
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