July 2004 - Boost - lists.preview.boost.org

RE: [boost] Re: Boost.Threads: Do we need all those mutexes?
by Batov, Vladimir 01 Jul '04

01 Jul '04

> Well, as you point out, try_lock is like a timed_lock with > time = 0, and lock is like a timed_lock with time = infinity, > so why not give timed_lock both lock() and try_lock() > methods as shorthand notation for lock(m, t=0) and > lock(m, t=infinity)? [Batov, Vladimir] Because, in my view, it violates the fundamental (and I think widely accepted) OO design principle (guideline?) that in simple terms can be expressed as "one class, one responsibility". Names like Bertrand Meyer, Herb Sutter and many others immediately come to mind. We can either achieve that by having a universal lock (with timed_lock as the basis) and shorthand notations in separate derived classes (lock, timed_lock and try_lock) or by keeping those three completely unrelated (probably at the expense of some code/functionality duplication). I am personally leaning towards latter, as even though technically all three concepts are related, from the user point of view they are distinct. > The argument for try_lock not having a blocking lock() method, > which you seem to stress more often, is much clearer; I'm much > more inclined to agree with you there. [Batov, Vladimir] Thank you. I feel that it is important that every class does what it promises to do. No more, no less.

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Converting Boost.Threads documentation to BoostBook
by Michael Glassford 01 Jul '04

01 Jul '04

I've just checked in the Boost.Threads documentation in BoostBook format and changed doc\src\boost.xml appropriately; is there anything else I need to do? Also, is the BoostBook documentation being regularly generated somewhere so that I can take a look at it and make sure everything is working properly somewhere besides my machine? Mike

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gcc thread local storage
by Neal D. Becker 01 Jul '04

01 Jul '04

I know almost nothing about threads. Still I thought this link might be of interest for boost::thread. I'm guessing that the term "Thread Local Storage" is the same as "Thread Static Storage". http://gcc.gnu.org/onlinedocs/gcc/Thread-Local.html

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RE: [boost] Re: Boost.Threads: Do we need all those mutexes?
by Batov, Vladimir 01 Jul '04

01 Jul '04

[Christopher Currie] In the need of extreme memory efficiency and speed: I already have, from prior use, a scoped_try_lock 'l' around my mutex, currently unlocked. I need to lock my mutex in a blocking fashion. I do not wish to pay the memory and time cost to create an instance of scoped_lock just to do this. I therefore call 'l.lock()' and not 'l.try_lock()'. [Batov, Vladimir] I am sorry but I am far from being convinced that "extreme memory efficiency" can be achieved by saving on one lock. Locks are very transient creatures and created on the stack. Commonly the stack is predefined by OS regardless if you use it or not. Consequently, even when you do not create another object on the stack, that memory is not available to you for anything else anyway. Even if it is, I greatly doubt that that approach is the right approach to achieve efficiency. The common approach would be to worry about the right design first and foremost, then run profilers/monitors/tests to see where we actually can save memory/gain performance. Twisting design for the sake of perceived performance/memory gains is often (I'd say always) a very bad idea. Even if you do not buy into my arguments in the prev. paragraph, you'll probably agree it'll be unfair to expect that the majority of library users and overall general-purpose library design need to pay the price of accommodating your very specific requirements. For example, general memory allocation is often slow for me. Then, I write my own special memory allocator. I am not asking for the general-purpose allocator to be changed. ... [Christopher Currie] Constructor parameters are, admittedly, a different discussion, and most of them boil down to syntactic sugar for a non-locking constructor and a call to some locking operation, blocking or otherwise. But (IMO) it's a useful syntactic sugar that *can* if used properly make programs less cumbersome to construct without sacrificing correctness or clarity. [Batov, Vladimir] I am not against syntactic sugar if it is in line with what is reasonably expected from a class. However, I am against syntactic sugar which is not relevant to class functionality. Like I am happy if I can simply give my credit card to a taxi driver and not worry about having cash. However, I am not sure if I'd like that driver singing. As far as S/W design is concerned, I'd prefer a taxi driver class (with its responsibilities) and a singer class (with its responsibilities). We all know how to blend those two classes if we ever need that.

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min, max, GCC 2.95.3, and STLport
by Doug Gregor 01 Jul '04

01 Jul '04

The new handling of min/max seems to break under GCC 2.95.3 with STLport. I'm not quite sure _why_ it doesn't work (I don't have the compiler around), but you can see the failure here: http://tinyurl.com/ytdlf Perhaps someone with that compiler/lib combination could get preprocessed output for the problem area so we could see what's happening? Doug

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Learning boost::MPL
by Dan 01 Jul '04

01 Jul '04

I'm trying to use iter_fold with a vector_c to compute the sum of all of the integers in the container. What I have is: template<typename Sequence> struct sum { typedef typename mpl::iter_fold< Sequence, typename mpl::begin<Sequence>::type, mpl::plus< mpl::deref<_1>, mpl::deref<_2> >; // ^ what should this really be? > // what do i put after here? }; Which obviously won't work. I don't know how to keep a running total as I iterate over the sequence with plus. Help! Thanks, -Dan

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ccref
by alnsn＠yandex.ru 01 Jul '04

01 Jul '04

This is not a typo, I'm trying to emphasize that ref, cref, ... sequence lacks one element which imposes more strict requirements on its argument. According to IQ tests logic that sequence should be continued with ccref :) If seriously, cref allows silent binding of a temporary to a reference. Apparently, this is not always fine. Inspired by N1610 (thanks to Dave and Gary) I've tried to detect both const and non-const rvalues. I didn't yet opened my copy of the standard to check it but the code seems to work on g++ 3.2.2, g++ 3.4.0, Intel 8.0 (all under linux) and Comeau online. #include <boost/ref.hpp> template<class T1, class T2> struct enable_if_same { }; template<class T> struct enable_if_same<T,T> { typedef int type; }; template<class T> boost::reference_wrapper<T const> const ccref(T volatile& r, typename enable_if_same<T,T const>::type = 0) { return boost::reference_wrapper<T const>(const_cast<T const&>(r)); } struct convertible_to_int { operator int() const { return 0; } }; template<class T> boost::reference_wrapper<T const> const ccref(T const volatile& r) { return boost::reference_wrapper<T const>(const_cast<T const&>(r)); } int rvalue() { return 0; } int const const_rvalue() { return 0; } int main() { int i; int const j = 0; ccref(i); ccref(j); // Try uncommenting any of these lines: // ccref(rvalue()); // ccref(const_rvalue()); } -- Alexander Nasonov

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Links at ACCU
by David Abrahams 01 Jul '04

01 Jul '04

Hi, I recently got this request from the ACCU website admins: Please take a look at www.accu.org/terse/cpp.htm and let me know how the Boost library/people would like to be represented on www.accu.org/terse/cpp.htm. So I figured I'd ask. Anyone have an opinion? -- Dave Abrahams Boost Consulting http://www.boost-consulting.com

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RE: [boost] Re: Cvs tag dependency
by Rozental, Gennadiy 01 Jul '04

01 Jul '04

> "Rozental, Gennadiy" <gennadiy.rozental(a)thomson.com> writes: > > > Hi, > > > > Inn a light of recent discussion on earlier freezing, I > have following > > question/proposition: > > > > Is it exist in Boost.Build or could we add feature that allow us to > > specify cvs tag dependency as a dependency grist? > > I _think_ what you're proposing is interesting, but the means > of getting there may be completely inappropriate for > Boost.Build, if I understand it at all. Why don't you try to > say what you're trying to accomplish without trying to design > the Boost.Build feature? I want to be able to use regression testing facility not only for HEAD cvs state. > Are you trying to get cvs checkout > actions into the build system? Namely. I want build system be aware about different versions of files/components and want to be able to specify which version I prefer to use for this particular test. > If so, why? What's wrong with doing > > cvs update -rwhatever_tag > before kicking off the test? Nothing. I just want it happened automatically on a computer that performs regression testing, depends on a rule defined in a Jamfile. > Dave Abrahams Gennadiy.

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