Re: AtomicCounter::is_always_lock_free on armel
Hi, On Fri, Nov 08, 2019 at 09:05:12AM +0100, Stephan Bergmann wrote: > Ah. What I'd meant was something like > > > #if ... > > using AtomicCounter = std::atomic>; > > static_assert(AtomicCounter::is_always_lock_free); > > #else > > using AtomicCounter = volatile std::make_unsigned_t; > > #endif OK. changed and updated in gerrit. Verified in a armel build on abel.debian.org and in my local amd64 build. Regards, Rene >
Re: AtomicCounter::is_always_lock_free on armel
On 07/11/2019 17:56, Rene Engelhard wrote: On Thu, Nov 07, 2019 at 10:18:06AM +0100, Stephan Bergmann wrote: I don't understand your "Given the introduced AtomicCounter is used later..." reasoning above, but commented at Obviously I meant static AtomicCounter gnEnterCount; which comes later (and wasn't there before) and uses the using AtomicCounter = [...] definition, so #ifdef'ing the whole block out would have been more invasive. Ah. What I'd meant was something like #if ... using AtomicCounter = std::atomic>; static_assert(AtomicCounter::is_always_lock_free); #else using AtomicCounter = volatile std::make_unsigned_t; #endif
Re: AtomicCounter::is_always_lock_free on armel
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如果可以，请将我从收件名单中剔除，谢谢！
发自我的 iPhone
> 在 2019年11月8日，上午12:56，Rene Engelhard 写道：
>
> Hi,
>
>> On Thu, Nov 07, 2019 at 10:18:06AM +0100, Stephan Bergmann wrote:
>>> On 06/11/2019 18:39, Rene Engelhard wrote:
>>> Given the introduced AtomicCounter is used later, too I tried the simplified
>>>
>>> diff --git a/vcl/inc/opengl/zone.hxx b/vcl/inc/opengl/zone.hxx
>>> index 3210186c3096..13ac3bf6793e 100644
>>> --- a/vcl/inc/opengl/zone.hxx
>>> +++ b/vcl/inc/opengl/zone.hxx
>>> @@ -36,7 +36,9 @@ class VCL_DLLPUBLIC OpenGLZone {
>>> // increasing, so will eventually overflow, so the underlying type
>>> better be unsigned, which
>>> // sig_atomic_t is not guaranteed to be:
>>> using AtomicCounter =
>>> std::atomic>;
>>> +#if !defined ARM32 && !defined __ARM_PCS_VFP
>>> static_assert(AtomicCounter::is_always_lock_free);
>>> +#endif
>>> /// how many times have we entered a GL zone
>>> static AtomicCounter gnEnterCount;
>>>
>>> (atking that define from bridges...)
>>>
>>> and that builds...
>>>
>>> -> https://gerrit.libreoffice.org/#/c/82165/
>>
>> I don't understand your "Given the introduced AtomicCounter is used
>> later..." reasoning above, but commented at
>
> Obviously I meant
>
> static AtomicCounter gnEnterCount;
>
> which comes later (and wasn't there before)
> and uses the using AtomicCounter = [...] definition, so
> #ifdef'ing the whole block out would have been more invasive.
>
>>
Re: AtomicCounter::is_always_lock_free on armel
Hi,
On Thu, Nov 07, 2019 at 10:18:06AM +0100, Stephan Bergmann wrote:
> On 06/11/2019 18:39, Rene Engelhard wrote:
> > Given the introduced AtomicCounter is used later, too I tried the simplified
> >
> > diff --git a/vcl/inc/opengl/zone.hxx b/vcl/inc/opengl/zone.hxx
> > index 3210186c3096..13ac3bf6793e 100644
> > --- a/vcl/inc/opengl/zone.hxx
> > +++ b/vcl/inc/opengl/zone.hxx
> > @@ -36,7 +36,9 @@ class VCL_DLLPUBLIC OpenGLZone {
> > // increasing, so will eventually overflow, so the underlying type
> > better be unsigned, which
> > // sig_atomic_t is not guaranteed to be:
> > using AtomicCounter =
> > std::atomic>;
> > +#if !defined ARM32 && !defined __ARM_PCS_VFP
> > static_assert(AtomicCounter::is_always_lock_free);
> > +#endif
> > /// how many times have we entered a GL zone
> > static AtomicCounter gnEnterCount;
> >
> > (atking that define from bridges...)
> >
> > and that builds...
> >
> > -> https://gerrit.libreoffice.org/#/c/82165/
>
> I don't understand your "Given the introduced AtomicCounter is used
> later..." reasoning above, but commented at
Obviously I meant
static AtomicCounter gnEnterCount;
which comes later (and wasn't there before)
and uses the using AtomicCounter = [...] definition, so
#ifdef'ing the whole block out would have been more invasive.
>
Re: AtomicCounter::is_always_lock_free on armel
On 06/11/2019 18:39, Rene Engelhard wrote:
Given the introduced AtomicCounter is used later, too I tried the simplified
diff --git a/vcl/inc/opengl/zone.hxx b/vcl/inc/opengl/zone.hxx
index 3210186c3096..13ac3bf6793e 100644
--- a/vcl/inc/opengl/zone.hxx
+++ b/vcl/inc/opengl/zone.hxx
@@ -36,7 +36,9 @@ class VCL_DLLPUBLIC OpenGLZone {
// increasing, so will eventually overflow, so the underlying type better
be unsigned, which
// sig_atomic_t is not guaranteed to be:
using AtomicCounter =
std::atomic>;
+#if !defined ARM32 && !defined __ARM_PCS_VFP
static_assert(AtomicCounter::is_always_lock_free);
+#endif
/// how many times have we entered a GL zone
static AtomicCounter gnEnterCount;
(atking that define from bridges...)
and that builds...
-> https://gerrit.libreoffice.org/#/c/82165/
I don't understand your "Given the introduced AtomicCounter is used
later..." reasoning above, but commented at
Re: AtomicCounter::is_always_lock_free on armel
On Wed, Nov 6, 2019 at 2:05 PM Rene Engelhard wrote: > (even though OpenGL is probably no thing on armel, I'd be wary to just > remove the assert...) FTR, OpenGL is available on armel, for example the Raspberry Pi devices have libre drivers for the VC4 GPU and some of them can only run Debian armel (or Raspbian armhf). -- bye, pabs https://wiki.debian.org/PaulWise
Re: AtomicCounter::is_always_lock_free on armel
Hi,
On Wed, Nov 06, 2019 at 09:26:53AM +0100, Stephan Bergmann wrote:
> > +// gnEnterCount and gnLeaveCount are accessed both from multiple
> > threads (cf.
> > +// OpenGLWatchdogThread::execute; so need to be of atomic type) and
> > from signal handlers (cf.
> > +// VCLExceptionSignal_impl; so need to be of lock-free atomic type).
> > sig_atomic_t is chosen as
> > +// the underlying type under the assumption that it is most likely to
> > lead to an atomic type
> > +// that is actually lock-free. However, gnEnterCount and gnLeaveCount
> > are both monotonically
> > +// increasing, so will eventually overflow, so the underlying type
> > better be unsigned, which
> > +// sig_atomic_t is not guaranteed to be:
> > +using AtomicCounter =
> > std::atomic>;
> > +static_assert(AtomicCounter::is_always_lock_free);
> >
> > Looking at
> > https://en.cppreference.com/w/cpp/atomic/atomic/is_always_lock_free it is
> > "/* implemtation defined */"
> > so is it always false on armel?
>
> Yeah, my hope was that we won't ever encounter platforms where this is
> false.
>
> > Does that mean we need to drop LibreOffice support on armel or is there
> > some way out of it?
> > (even though OpenGL is probably no thing on armel, I'd be wary to just
> > remove the assert...)
>
> Given that the code used "static volatile sal_uInt64" for
> genEnter/LeaveCount before ec17c8ec5256386b0197a8ffe5d7cad3e7d70f8f, we
> don't make things worse than they originally were if we fall back to that
> type again on armel. So if the original code happened to work well enough
> on armel in practice, you could add an appropriate #if/else (with a useful
> comment) around the definition of AtomicCounter and the accompanying
> static_assert. (And address any resulting -Wvolatile on armel as
> appropriate for your needs.)
Given the introduced AtomicCounter is used later, too I tried the simplified
diff --git a/vcl/inc/opengl/zone.hxx b/vcl/inc/opengl/zone.hxx
index 3210186c3096..13ac3bf6793e 100644
--- a/vcl/inc/opengl/zone.hxx
+++ b/vcl/inc/opengl/zone.hxx
@@ -36,7 +36,9 @@ class VCL_DLLPUBLIC OpenGLZone {
// increasing, so will eventually overflow, so the underlying type better
be unsigned, which
// sig_atomic_t is not guaranteed to be:
using AtomicCounter = std::atomic>;
+#if !defined ARM32 && !defined __ARM_PCS_VFP
static_assert(AtomicCounter::is_always_lock_free);
+#endif
/// how many times have we entered a GL zone
static AtomicCounter gnEnterCount;
(atking that define from bridges...)
and that builds...
-> https://gerrit.libreoffice.org/#/c/82165/
Regards,
Rene
Re: AtomicCounter::is_always_lock_free on armel
On 06/11/2019 10:47, rene.engelh...@mailbox.org wrote: Am 6. November 2019 09:26:53 MEZ schrieb Stephan Bergmann : , you could add an appropriate #if/else (with a useful comment) around the definition of AtomicCounter and the accompanying static_assert. Can do, yes, although I would like it more if it was fine upstream... That's what I meant, provide an upstream commit. (And address any resulting -Wvolatile on armel as appropriate for your needs.) As it (is it?) only a warning one can also just ignore it ;-) Yes, that's likely all you need to do to address it appropriately for your needs.
Re: AtomicCounter::is_always_lock_free on armel
Hi, Am 6. November 2019 09:26:53 MEZ schrieb Stephan Bergmann : >don't make things worse than they originally were if we fall back to >that type again on armel. So if the original code happened to work >well >enough on armel in practice It built. No more data ;-) , you could add an appropriate #if/else >(with >a useful comment) around the definition of AtomicCounter and the >accompanying static_assert. Can do, yes, although I would like it more if it was fine upstream... > (And address any resulting -Wvolatile on >armel as appropriate for your needs.) As it (is it?) only a warning one can also just ignore it ;-) Regards Rene -- Diese Nachricht wurde von meinem Android-Gerät mit K-9 Mail gesendet.
Re: AtomicCounter::is_always_lock_free on armel
[assuming
Cc: "libreoff...@lists.freedesktop.org Stephan Bergmann"
was a typo, and the original mail was meant to be sent to
libreoff...@lists.freedesktop.org]
On 06/11/2019 07:05, Rene Engelhard wrote:
LibreOffice 6.4.0 alpha1 was just accepted into Debian experimental and failed
on armel
(old arm gnueabi):
In file included from /<>/vcl/source/app/svmain.cxx:90:
/<>/vcl/inc/opengl/zone.hxx:39:34: error: static assertion failed
39 | static_assert(AtomicCounter::is_always_lock_free);
| ~~~^~~
make[2]: *** [/<>/solenv/gbuild/LinkTarget.mk:296:
/<>/workdir/CxxObject/vcl/source/app/svmain.o] Error 1
If I run git blame/log I see
commit ec17c8ec5256386b0197a8ffe5d7cad3e7d70f8f
Author: Stephan Bergmann
Date: Tue Sep 17 20:39:43 2019 +0200
-Werror=volatile in OpenGLZone
Recent GCC 10 trunk in C++20 mode reports issues like
> vcl/inc/opengl/zone.hxx:37:21: error: ‘++’ expression of ‘volatile’-qualified type is deprecated [-Werror=volatile]
>37 | OpenGLZone() { gnEnterCount++; }
> | ^~~~
so look for a type that is more appropriate here (see the comment added to
vcl/inc/opengl/zone.hxx for details). (Though calls like
OpenGLZone::isInZone(), comparing gnEnterCount and gnLeaveCount, in
OpenGLWatchdogThread::execute are still not done atomically, of course.)
Change-Id: Ie5563addc65f629336f89cbccb73f7b9ac5e9870
Reviewed-on: https://gerrit.libreoffice.org/79072
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann
which added
+// gnEnterCount and gnLeaveCount are accessed both from multiple threads
(cf.
+// OpenGLWatchdogThread::execute; so need to be of atomic type) and from
signal handlers (cf.
+// VCLExceptionSignal_impl; so need to be of lock-free atomic type).
sig_atomic_t is chosen as
+// the underlying type under the assumption that it is most likely to lead
to an atomic type
+// that is actually lock-free. However, gnEnterCount and gnLeaveCount are
both monotonically
+// increasing, so will eventually overflow, so the underlying type better
be unsigned, which
+// sig_atomic_t is not guaranteed to be:
+using AtomicCounter = std::atomic>;
+static_assert(AtomicCounter::is_always_lock_free);
Looking at https://en.cppreference.com/w/cpp/atomic/atomic/is_always_lock_free it is
"/* implemtation defined */"
so is it always false on armel?
Yeah, my hope was that we won't ever encounter platforms where this is
false.
Does that mean we need to drop LibreOffice support on armel or is there some
way out of it?
(even though OpenGL is probably no thing on armel, I'd be wary to just
remove the assert...)
Given that the code used "static volatile sal_uInt64" for
genEnter/LeaveCount before ec17c8ec5256386b0197a8ffe5d7cad3e7d70f8f, we
don't make things worse than they originally were if we fall back to
that type again on armel. So if the original code happened to work well
enough on armel in practice, you could add an appropriate #if/else (with
a useful comment) around the definition of AtomicCounter and the
accompanying static_assert. (And address any resulting -Wvolatile on
armel as appropriate for your needs.)
