Re: why boost:shared_ptr so slower?

From:

"Chris M. Thomasson" <no@spam.invalid>

Newsgroups:

comp.lang.c++

Date:

Fri, 21 Aug 2009 06:59:26 -0700

Message-ID:

<h6m97p$2gj6$1@news.ett.com.ua>

"Chris M. Thomasson" <no@spam.invalid> wrote in message
news:h6m7gt$2f6k$1@news.ett.com.ua...

"Juha Nieminen" <nospam@thanks.invalid> wrote in message
news:%Djjm.223$1Y6.48@read4.inet.fi...

Keith H Duggar wrote:

Boost shared_ptr is not "thread safe" by any standard that is
usually meant by the term:

http://www.boost.org/doc/libs/1_39_0/libs/smart_ptr/shared_ptr.htm#ThreadSafety

First you claim that it's not thread-safe, and then you point to the
documentation which says that it is.

ie "the same level of thread safety as built-in types" means
not "thread safe".

You are confusing two different types of thread-safety.

[...]

FWIW, Boost shared_ptr only provides basic/normal thread-safety. It does
NOT provide strong thread-safety in any way shape or form. Read the entire
following thread:

http://groups.google.com/group/comp.programming.threads/browse_frm/thread/e5167941d32340c6/1b2e1c98fa9ad7c7

You simply cannot use shared_ptr in a scenario which demands strong thread
safety level. For example, this will NOT work:
_______________________________________________________________
static shared_ptr<foo> global_foo;

void writer_threads() {
for (;;) {
   shared_ptr<foo> local_foo(new foo);
   global_foo = local_foo;
}
}

void reader_threads() {
for (;;) {
   shared_ptr<foo> local_foo(global_foo);
   local_foo->read_only_operation()();
}
}
_______________________________________________________________

[...]

Here is a pre-alpha implementation of my experimental strongly thread-safe
reference counting algorithm:

http://webpages.charter.net/appcore/vzoom/refcount

Here is some very crude documentation of the C API:

http://webpages.charter.net/appcore/vzoom/refcount/doc

I proposed this algorithm for Boost a while ago, but I never really followed
up on it and did not make a formal proposal. Here are the relevant posts:

http://search.gmane.org/?query=&group=gmane.comp.lib.boost.devel&author=chris%20thomasson

Here is a fairly detailed description of exactly how the "strong
thread-safety aspect" of the algorithm works:

http://article.gmane.org/gmane.comp.lib.boost.devel/149803

Enjoy!

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