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Subject: Re: Apr 8th Sg14 monthly call agenda
From: connor horman (chorman64_at_[hidden])
Date: 2020-04-08 15:30:45


With respect to the implementation code for the paper shown at today's
meeting, I would be very interested to take a look at it, and maybe poke
around. If its needed, my github username is chorman0773.

On Wed, Apr 8, 2020 at 16:00 Michael Wong via SG14 <sg14_at_[hidden]>
wrote:

>
>
> On Wed, Apr 8, 2020 at 11:55 AM Michael Wong <fraggamuffin_at_[hidden]>
> wrote:
>
>> Topic: SG14 Low Latency Monthly. Hi all, I have turned on high security
>> for this call in light of recent events.
>>
>> Hi,
>>
>> Michael Wong is inviting you to a scheduled Zoom meeting.
>>
>> Topic: SG14 monthly Apr 2020-Oct 2020
>> Time: Apr 8, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: May 13, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: June 10, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Jul 8, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Aug 12, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Sep 9, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Oct 14, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Join from PC, Mac, Linux, iOS or Android:
>> https://iso.zoom.us/j/819108882?pwd=L0pPZm5QRWlTYXdJditvU1JLdjFYUT09
>> Password: 013549
>>
>> Or iPhone one-tap :
>> US: +13462487799,,819108882# or +14086380968,,819108882#
>> Or Telephone:
>> Dial(for higher quality, dial a number based on your current
>> location):
>> US: +1 346 248 7799 or +1 408 638 0968 or +1 646 876 9923 or
>> +1 669 900 6833 or +1 253 215 8782 or +1 301 715 8592 or +1 312 626 6799
>> or 877 853 5247 (Toll Free)
>> Meeting ID: 819 108 882
>> Password: 013549
>> International numbers available: https://iso.zoom.us/u/abhaIjFKLZ
>>
>> Or Skype for Business (Lync):
>> https://iso.zoom.us/skype/819108882
>>
>>
>>
>> Agenda:
>>
>> 1. Opening and introductions
>>
>> 1.1 Roll call of participants
>>
> Derek Haines
> Henry Miller
> James renwick
> Andrews Weis
> Antony Peacock
> ben Craig, Ben Saks
> BillyBaker
> Connor Horman
> Max Gardner
> Patrice Roy
> Paul Bendien
> Sophia Poirier
> Staffan Tjernstrom
> Steven Varga
> Jens Maurer
> Inbal Levi
> Michael Wong
> Dan Raviv?
> Charles Bay
> Matthew Butler
>
>
>
>
>
>
>
> 1.2 Adopt agenda
>>
> Approve.
>
>> 1.3 Approve minutes from previous meeting, and approve publishing
>> previously approved minutes to ISOCPP.org
>>
> Approve.
>
>>
>> 1.4 Action items from previous meetings
>>
>> 2. Main issues (125 min)
>>
>> 2.1 General logistics
>>
>> Prague summary
>>
>> Mailing deadline is monthly on 15th
>>
>> All meetings going online.
>>
>> 2.2 Paper reviews
>>
>>
>> Low-cost Deterministic C++ Exceptions for Embedded Systems
>> <https://www.research.ed.ac.uk/portal/files/78829292/low_cost_deterministic_C_exceptions_for_embedded_systems.pdf> Low-cost
>> Deterministic C++ Exceptions for Embedded Systems James Renwick James
>> Renwick et al.
>>
> BC: passing an address, so you can indirect jmp instead of return?
> leave optimzation off for now, what it this just look like normal code
>
> when propagating exception up the call stack, just do a return
> BC: regular processor, branch cost is small, but on gpu divergign control
> throws is high, throwing an exception on gpu is already expensive
> for gpu instead of terminate might do a HW specific thing
> CH: too many banches will cross bank boundaries;
> Even with a nave implementaion, we can see n times better
>
> ST: precompield external libraries 1K allocated for stack and with only
> 256 bytes from the stack, what happens? Right we dont deal with dynamic
> library yet, but it doesnt make teh exception object unique, and nothing is
> unique on the exception object here
> DLL and static libraries crossing boundary may be UB here or an ODR
> violation
>
> JM: table reduction does not match waht you said about text increase
> maching?
> because unwind library is gone
>
> BC: version of clang?
> clang 6
>
> CH:on function size vs binary size;
> should the catch block, which can be called out to another function,
>
> buffer on where to put EH object and it falls back to the heap, so this
> can do the same thing
> need to inject parameter, which could thow., need to distinguisj C and C++
> function so need throw specifier added, abi change
> or pass by TLS
>
> a C language linkage, dont inject, standards says thata fn pointer inside
> a structure,
> type of ptr
> extern C allowed to throw, so we can detect what linkage a fn has
> C adapting deterministic exception
> we just need implmentation with a compielr flag
> parameter injection will be an abi break
>
> exception_ptr was intended to allow copying to support bot hreference
> counting heap allocated as is eager copy implementations
>
> you know the size because you call the copy constructor and not just
> memcpy it
> resolve copy construction when you write the throw expression so you know
> the size of the xception object
> but if pass exception ptr through to another functions object, that could
> take a dynamic size,
> if you can pass exception ptr around, can assign it to global variable,
> stack space does not matter, you have a life time problem; so it has to be
> on the heap to solve this
> so if eh object lives on stack, cant touch the heap, the nwe have a
> problem; yes you can outlive, so copy an exception ptr object stackframe,
> then for these reasons
> exception_ptr is aimed at heap implementation
> so we propose similar that is agnostic, encapsulate exception object, call
> get_current exception, then you are responsible for this object, no
> reference count, so you move it around
>
> cross noexcept bounday with an exception ptr, want to pass exeption
> through noexcept boundary without passing exception object as parameter for
> the rethrowing case
>
> want std exception ptr that has shared ownership and unique ownership of
> the exception object
>
> no language or library changes in this paper
> its an implementation report
> should we advise exception ptr is toxic
>
> Paul: claims is standard conformant, leaves out what noexcept specifier
> mean
>
> Ben: it would no changes, there are proposal would be changing stuff
> substantially, address cost benefit analysis of those papers
>
> some of the mitigation: adding noexcept blocks to mark large parts as
> noexcept, change the calling convention to make it so a prebuilt C library
> can work with this
>
> PB: C assert is verymuch a hint of adoption
>
> Exception_ptr: can we ban it in free_standing, or use Rust send
>
> exception_ptr on the heap is fine, problem is when you move it, it is
> nolonger available in the catch block, if you copy exception its fine as
> implementation only allow move only objects
>
> if it is moved onto the heap, then its a problem, but OK if you copy from
> stack to heap
>
> open the github (limited form)and form a group and tthen come back to
> discuss bridfing mechanism
>
> please reply to this thread if inetersted in joining this Exception
> Handing for Embedded implementation group.
>
> P2057r0
>> <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2020/p2057r0.pdf> SG14
>> SG19 Past, Present and Future status Michael Wong Michael Wong et al.
>>
>>
> PB: numeric proposal an ommission?Yes please add
>
>> 2.2.1 any other proposal for reviews?
>>
> MW: Interested in Networking RPC proposal? Yes
> ST: Error handling compendium?
>
>> 2.3 Domain-specific discussions
>>
>> 2.3.1 SIG chairs
>>
>> - Embedded Programming chairs: Ben Craig, Wouter van Ooijen and Odin
>> Holmes, John McFarlane
>> <
>>
>> http://wiki.edg.com/bin/edit/Wg21belfast/McFarlane?topicparent=Wg21belfast.SG14CPPCON2019-09-17;nowysiwyg=1>
>>
>>
>> - Financial/Trading chairs: Stephan TJ, Carl Cooke, Neal Horlock,
>> Mateusz Pusz, Clay Trychta,
>> - Games chairs: Rene Riviera, Guy Davidson and Paul Hampson
>> - Linear Algebra chairs: Bob Steagall, Mark Hoemmen, Guy Davidson
>>
>> 2.4 Other Papers and proposals
>>
>> 2.5 Future F2F meetings:
>>
>> 2.6 future C++ Standard meetings:
>> https://isocpp.org/std/meetings-and-participation/upcoming-meetings
>>
>> - 2020-11: (New York, tentative)
>> - 2021-02-22 to 27: Kona, HI, USA
>>
>> 3. Any other business
>> Reflector
>> https://lists.isocpp.org/mailman/listinfo.cgi/sg14
>> As well as look through papers marked "SG14" in recent standards
>> committee
>> paper mailings:
>> http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/
>> http://open-std.org/jtc1/sc22/wg21/docs/papers/2016/
>>
>> Code and proposal Staging area
>> https://github.com/WG21-SG14/SG14
>> 4. Review
>>
>> 4.1 Review and approve resolutions and issues [e.g., changes to SG's
>> working draft]
>>
>> 4.2 Review action items (5 min)
>>
>> 5. Closing process
>>
>> 5.1 Establish next agenda
>>
>> 5.2 Future meeting
>>
>> Time: May 13, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: June 10, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Jul 8, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Aug 12, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Sep 9, 2020 02:00 PM Eastern Time (US and Canada)
>>
>> Time: Oct 14, 2020 02:00 PM Eastern Time (US and Canada)
>>
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