Friday, November 15, 2019

Digest for comp.lang.c++@googlegroups.com - 4 updates in 2 topics

Sam <sam@email-scan.com>: Nov 15 05:18PM -0500

Bonita Montero writes:
 
> the exception-object couldn't be created. There are several heap-alloca-
> tion-strategies which are all equally appropriate for this purpose.
> Heap-allocation is a different topic.
 
Look, it's ok that you don't know this, and you have no idea how it works.
Nobody's perfect. Don't let it upset you.
"Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: Nov 15 01:56PM -0800

On 11/15/2019 1:47 PM, Scott Lurndal wrote:
>> and proper padding? Its used to avoid false sharing.
 
> Why do you bother with BM? It deliberatly removes attributes so
> it's impossible to see who said what to whom.
 
I think BM = JG. Its a sock puppet...
 
 
> I suspect that most architectures avoid supporting unaligned atomics
> because they might split cache lines which would make it impossible
> (or very time consuming) to support atomic semantics for the access.
 
Well, I remember abusing unaligned atomics such that a word straddles a
L2 cache line! Well, on x86 this should trigger a system wide bus lock
for legacy reasons. It did something quite interesting. It acted like a
remote memory barrier that makes it possible to implement asymmetric
sync algorithms. There is a mention of it, need to find it. They called
it something like QPI? Humm... Let me do a little search...
 
[searching]
 
Found it!
 
https://blogs.oracle.com/dave/qpi-quiescence
 
This is very hackish, but does allow for RCU. Also, fwiw, Windows has an
interesting instruction:
 
https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-flushprocesswritebuffers
 
That can provide a similar behavior. Iirc, it sends IPIs to an affinity
mask of processors. This can be done in the Kernel with Windows. It
takes a device driver.
"Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>: Nov 15 01:59PM -0800

On 11/15/2019 1:47 PM, Scott Lurndal wrote:
>> and proper padding? Its used to avoid false sharing.
 
> Why do you bother with BM? It deliberatly removes attributes so
> it's impossible to see who said what to whom.
[...]
 
Actually, I have asked it to use proper quoting for some time now. Also,
it acts like the following thing:
 
https://zork.fandom.com/wiki/Cruel_Puppet
 
Sometimes, it feels like I am casting my pearls before something... ;^o
 
Might have to stop feeding it.
Ian Collins <ian-news@hotmail.com>: Nov 16 11:08AM +1300

On 16/11/2019 10:59, Chris M. Thomasson wrote:
 
> https://zork.fandom.com/wiki/Cruel_Puppet
 
> Sometimes, it feels like I am casting my pearls before something... ;^o
 
> Might have to stop feeding it.
 
Please do!
 
--
Ian.
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