[PATCH 2/2] PR libstdc++/41861 Add full steady_clock support to condition_variable

[Mike Crowe]

On Wednesday 04 September 2019 at 17:14:30 +0100, Jonathan Wakely wrote:
> On 04/09/19 15:49 +0100, Mike Crowe wrote:
> > On Wednesday 04 September 2019 at 14:39:35 +0100, Jonathan Wakely wrote:
> > > I noticed that the new tests you added in [PATCH 1/2] pass on current
> > > trunk, even without [PATCH 2/2], is that expected?
> > 
> > Unfortunately, yes. CLOCK_MONOTONIC and CLOCK_REALTIME will tick at the
> > same rate, so unless someone warps CLOCK_REALTIME during the test we can't
> > tell the difference between the old implementation of translating
> > steady_clock to system_clock and the new implementation that uses
> > steady_clock directly. :( I added the tests in the hope of finding other
> > mistakes in the new implementation rather than to reproduce the original
> > problem.
> 
> OK, that was what I figured was the case. Thanks for confirming.
> 
> > Maybe I should add comments to the test to make that clear along the lines
> > of those found in testsuite/27_io/objects/char/3_xin.cc ?
> 
> More comments are usually useful, otherwise I'll just ask the same
> question again and again :-)

How about something like:

--8<--
It's not possible for this test to automatically ensure that the
system_clock test cases result in a wait on CLOCK_REALTIME and steady_clock
test cases result in a wait on CLOCK_MONOTONIC. It's recommended to run the
test under strace(1) and check whether the expected futex calls are made by
glibc.
-->8--

Unfortunately I'm unable to determine how I actually managed to run the
test under strace. Perhaps I just compiled a similar test myself rather
than using dejagnu. :(

Mike.