Re: atomic counter

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sat, 15 Oct 2011 08:56:22 -0700 (PDT)

Message-ID:

<2011101510320144677-pete@versatilecodingcom>

On 2011-10-15 12:16:45 +0000, Alexander Terekhov said:

Increments for reference counting under basic thread-safety can be
memory_order_relaxed without any fences.
Decrements for reference counting under basic thread-safety can be
memory_order_relaxed without memory_order_acquire fence for the case
when resulting value of decrement == zero if referenced counted object
is immutable.
Decrements for reference counting under basic thread-safety can be
memory_order_relaxed with more relaxed fence than memory_order_release
for the case when resulting value of decrement != zero if referenced
counted object is immutable. I call such a fence "sink load barrier"
(release = "sink load barrier" + "sink store barrier").

All this recalls my original, somewhat tongue in cheek, objection to putting thread support into C++: it encourages programmers to try to do things that they don't understand.

Not that Alexander Terekhov doesn't understand this, but most people reading this thread won't understand it (including me).

That's why most programmers should stick to sequentially consistent program models. They're easier to analyze and easier to get right.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The Standard C++ Library Extensions: a Tutorial and Reference (www.petebecker.com/tr1book)

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