Re: shared_ptr from dinkumware ... comments??

"Peter Dimov" <>
22 Oct 2006 18:57:34 -0400
James Kanze wrote:

Having said that, of course, shared_ptr is one of the oldest
components in Boost, and I'm pretty sure that it is now stable
enough to be used in a production environment. As far as I
know, it is also pure template code, entirely contained in its
headers, and (at least for the non-threaded version) could be
installed just by copying the headers, without going through the
hassle of installing Boost (a real pain). And while there are
probably minor bugs in any version, like Pete, I doubt you'd
encounter problems in a typical application.

shared_ptr has been stable for use in production environments for
years. It hasn't changed much since 2003. Boost.Test, the testing
infrastructure for most of Boost, depends on shared_ptr, so it has to
work across the board, or every test fails. :-) The threaded version is
header-only, too. If you know of a minor bug, please let me know. We
don't tolerate bugs, however minor.

Unless, of course, you are trying to use a multi-threaded
version. Then, I'd be very sceptical. But IMHO, shared_ptr
isn't something you'd want to cross a thread boundary anyway.
(If the g++ version uses their atomic_add, there's a problem
with the Sparc 32 bit version, for example, which can cause the
process to pause unnecessarily in some cases; if the OS
implements real-time threads, the process can even block
completely due to priority inversion. And if it doesn't, it
means a pthread_mutex_lock per increment or decrement. 100%
correct, but likely to be a bit slow.)

Using shared_ptr in a threaded environment does increase the chance of
encountering a problem (mainly for non-x86 platforms) since we now use
a lock-free algorithm, and in the absence of a portable atomic
operations library (something that will be addressed by C++0x), this is
platform/compiler specific. We do fix the bugs as soon as we discover
them, though. :-)

We have a version for Sparc (contributed by Piotr Wyderski), but it
won't be in the upcoming 1.34 release, so you're right about the
current version using a mutex on this platform. g++'s own
std::tr1::shared_ptr (which is based on boost::shared_ptr) is, I
believe, lock-free on Sparc. I don't know about Dinkumware's.

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