Re: C++ Threads, what's the status quo?

"Peter Dimov" <>
11 Jan 2007 13:22:43 -0500
Mirek Fidler wrote:

Peter Dimov wrote:

Mirek Fidler wrote:

Well, I am not sure. Consider internal caches implemented using


members (or, heavens forbid, const_cast ;). In that case, your "basic"
requirement would mean that ALL mutable members must have


(locking) around them. That is IMO not a very good idea.

You get to choose the thread safety level for your component. If you
want concurrent reads to not be allowed, then you document them to not
be. "Default is basic" only says what happens when you don't explicitly
state otherwise.

Well, maybe it would be defined one more level between "basic" and "no"
to make me calm ;)

"Basic" sounds "minimal", but it is not minimal.

It really is basic, unless single-threaded code is a major factor. The
"minimal" level does not gain performance on average because from the
outside you are usually forced to use locks, whereas the component is
(in principle) able to provide "basic" using a lock-free container as a
cache. It can also use a rwlock and not serialize the cache hit path
(which also offers better lock granularity). In some cases it can
decide to bypass the cache completely for certain requests. And so on.
The overall theme is that it is the component that does (or doesn't do)
the sharing, not the user, so it can best decide how or whether to
protect itself.

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