November 2011 - Boost - lists.preview.boost.org

Boost.Algorithm design question
by Marshall Clow 03 Nov '11

03 Nov '11

So, what do people prefer (and why?): template<typename InputIterator, typename V> bool none_of_equal ( InputIterator first, InputIterator last, V const &val ) { for ( ; first != last; ++first ) if ( val == *first ) return false; return true; } or template<typename InputIterator, > bool none_of_equal ( InputIterator first, InputIterator last, iterator_traits<InputIterator>::value_type const &val ) { for ( ; first != last; ++first ) if ( val == *first ) return false; return true; } In the first case, I think there's (possible) conversion from V to iterator_traits<InputIterator>::value_type each time through the loop. In the second case, there is not. Of course, the (mythical?) smart compiler would do the conversion once and save the result for reuse. -- Marshall Marshall Clow Idio Software <mailto:mclow.lists@gmail.com> A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait). -- Yu Suzuki

17 79

[1.48.0 Beta 1][fusion] MacTypes.h conflict with nil
by Jeff Flinn 03 Nov '11

03 Nov '11

reposted from "[1.48.0] Beta 1 is now available from SourceForge" thread for better visibilty. Mac 10.6 Xcode 3.2.6 gcc 4.2: In compiling our application, upgrading from boost_1_44_0 I get conflicts with MacTypes.h define of nil when compiling cons_fwd.hpp from fusion. Any thoughts? Jeff

3 3

Interest in boost.deepcopy
by Allan Johns 02 Nov '11

02 Nov '11

Just gauging initial interest in a boost.deepcopy library, analogous to deepcopy in python. Each type would register deepcopy behaviour with the library (there are similarities to boost.serialize). Boost.deepcopy would supply out-of-the-box registration for pod types, pointer types, arrays, stl containers and common boost containers. Example: template<typename T> void deepcopy(deepcopycontext& ctxt, const T& obj) { ...; } Why not use boost::serialize and serialize into memory then out again I hear you say? That's a great approach, but only when every object requires the same deepcopy behaviour (also, it's not too optimal). The problem is, I need specific behaviour in some types. Specifically, I need copy-on-write behaviour for a Buffer class that I'm using. For example: void deepcopy(deepcopycontext& ctxt, const Buf& b) { if(!ctxt.contains(&b)) { Buf b2(b); // doesn't copy the buf data, just holds a shared ptr internally. Data is only cloned when b/b2 is written to ctxt.insert(&b, b2); } } I attempted to model this a while ago using boost.serialize, but it turned out pretty clunky, I started needing a few decorator classes for special cases, etc. Apologies for the oversimplified examples above, just wanting to get interest in the jist of it. Please let me know if this overlaps with existing boost functionality also (I'm not aware of anything atm). Feedback appreciated. Thx, Allan

9 18

[ratio] Request for permission to merge to release branch
by Vicente J. Botet Escriba 02 Nov '11

02 Nov '11

Hi, I want to merge https://svn.boost.org/trac/boost/changeset/75240 to the release branch. The modifications are minor and correct to tickets: https://svn.boost.org/trac/boost/ticket/5724 and https://svn.boost.org/trac/boost/ticket/6082. Best, Vicente

3 3

[multi_array] Ticket#4874 "multi_array compile errors using Visual C++ 2010 in debug mode"
by Stephan T. Lavavej 02 Nov '11

02 Nov '11

Hi Boost devs, VC10 users are occasionally encountering https://svn.boost.org/trac/boost/ticket/4874 and reporting it to MS. For example, see http://connect.microsoft.com/VisualStudio/feedback/details/687655/compilati… where I've explained what's going on (I wrote this analysis back in Feb 2010 and I believe it's still correct): The problem is that multi_array iterators report themselves as input iterators, which can't be written to (e.g. as the destination of a copy()). Under IDL=0, copy() doesn't actually care how its destination iterator is marked with an iterator category tag, it just tries to write to the destination iterator, and that works. Under IDL > 0, copy() wants to know whether its source and destination iterators are both random-access, in which case it can perform a range check and unwrap the destination iterator for increased performance. It does this by overloading foo(input_iterator_tag, output_iterator_tag) and foo(random_access_iterator_tag, random_access_iterator_tag) and calling foo(category(source), category(destination)). If both source and destination are random-access, both overloads are viable (i.e. callable) and the second overload is preferred, so it's actually called. Otherwise, source is required to be at least an input iterator (maybe stronger) and destination is required to be at least an output iterator (maybe stronger) so the first overload must be viable and the second overload will be non-viable, so the first overload wins by default. However, if the destination is not marked as an output iterator or stronger, then the first overload is non-viable as well as the second, so overload resolution fails and boom. Thanks, Stephan T. Lavavej Visual C++ Libraries Developer

2 1

boost mapped_file issue
by dophine 02 Nov '11

02 Nov '11

Hi all, I try to use memory map file. However, I don't know why the readsome return 0. It is fine if I use getline. int main(int argc,char *argv[]) { boost::iostreams::mapped_file_source source(argv[1]); boost::iostreams::stream<boost::iostreams::mapped_file_source> input(source); while(!input.eof()) { char b[1]; streamsize iRet = input.readsome(b, 1); cout << iRet << endl; cout << b[iRet]; } //std::string line; //while(std::getline(input, line)) { // std::cout << "Line: " << line << std::endl; //} return 1; } -- View this message in context: http://boost.2283326.n4.nabble.com/boost-mapped-file-issue-tp3971495p397149… Sent from the Boost - Dev mailing list archive at Nabble.com.

2 2

[locale] Premission to merge clang bugfix changeset to release tree
by Artyom Beilis 02 Nov '11

02 Nov '11

Hello, I'd like to ask a permission to merge a changeset 75174 from trunk to release tree. It is a fix of build issue under clang-2.9 and clang-3.0. See: https://svn.boost.org/trac/boost/changeset/75174 The changeset itself: ------------------------- Index: /trunk/libs/locale/src/posix/codecvt.cpp =================================================================== --- /trunk/libs/locale/src/posix/codecvt.cpp (revision 73382) +++ /trunk/libs/locale/src/posix/codecvt.cpp (revision 75174) @@ -135,5 +135,5 @@ // maybe illegal or may be double byte - char inseq[3] = {seq0 , begin[1], 0}; + char inseq[3] = { static_cast<char>(seq0) , begin[1], 0}; char *inbuf = inseq; size_t insize = 3; ------------------------- It solves build issues as I can see at trunk tests. Thanks, Artyom Beilis -------------- CppCMS - C++ Web Framework: http://cppcms.sf.net/ CppDB - C++ SQL Connectivity: http://cppcms.sf.net/sql/cppdb/

3 2

[atomic] comments
by Tim Blechmann 01 Nov '11

01 Nov '11

hi helge and others, ... has been rather quiet about the boost.atomic review, so i want to raise a view issues: shared memory support: the fallback implementation relies on the spinlock pool that also used by the smart pointers. however this pool is per-process, so the fallback implementation won't work in shared memory. can this be changed/fixed? atomic::is_lock_free(): is_lock_free is set to either `true' or `false'. however in some cases, there are alignment constraints (iirc, 64bit atomics on ia32/x86_64 require a 64bit alignment). afaict there are not precautions to take care of this, are there? compile-time vs run-time dispatching: some instructions are not available on every CPU of a specific architecture. e.g. cmpxchg8b or cmpxchg16b are not available on all ia32/x86_64 cpus. i would appreciate if these instructions would not be used before performing a CPUID check, whether these instructions are really available (at least in a legacy mode) cmpxchg16b: currently cmpxchg16b doesn't seem to be supported. this instruction is required for some lock-free data structures (e.g. there is a dequeue algorithm, that requires a pair of tagged pointers). maybe this can be a starting point to discuss boost.atomic ... cheers, tim

6 38

Re: [boost] [atomic] comments
by Helge Bahmann 01 Nov '11

01 Nov '11

> > > > > e.g. i would not trust on accessing sockets from a > > > > > real-time thread. > > > > > > > > what makes you believe that message channels in real-time systems > > > > were > > > > designed so dumb as to make them unusable for real-time purposes? > > > > > > life would be so much easier for me, if the users of my software would > > > not run on off-the-shelf operating systems ;) > > > > and what makes you believe that the performance characteristics of > > sockets in off-the-shelf operating systems is unsuitable for real-time, > > while the process scheduling characteristics of process scheduling in > > off-the-shelf operating systems is suitable for real-time? > > i cannot comment on windows, but both osx and linux provide ways to > schedule a thread at a priority that it won't be preempted by any other > thread, so the process scheduler won't interfere. that answers the second part but not the first (and is getting off-topic from atomic operations) > > > > right, but the standard implementation for gcc does not use a > > > > spinlock > > > > per object (see __atomic_flag_for_address) which turns all of this > > > > moot - there is NO guarantee for std::atomic to be safe > > > > interprocess, period> > > > > > > well, i'd say this is a problem of gcc's implementation of std::atomic. > > > this doesn't justify that boost.atomic does not follow the suggestion > > > of the standard. > > > > the standard says "should" not "must" -- the gcc guys have not made this > > decision without good reasons, and I agree with these reasons > > > > note that there is also trouble lurking with run-time selection of > > whether something like atomic<uint64_t> is atomic via cmpxchg8b: do you > > really want to make this at minimum 12 bytes in size (though effectively > > occupying 16 due to alignment) just to save the room for the > > rarely-if-ever used per-object spinlock? same with atomic<128> and > > cmpxchg16b ? > > i don't really care about the size of an atomic<>. but I *do* care and believe it or not there are people writing applications that are memory-bound (doubling the overhead of the reference count in each of several millions of objects is *not* funny) > one other point for > runtime selection is compatibility. e.g. you may have two binaries, one is > compiled with support for double-width CAS, the other one without. with > compile-time dispatching the behavior would be undefined, with run-time > selection, it would be handled gracefully ... I don't quite understand the point -- quite obviously nothing good will happen if the applications do not agree on a protocol, and there is nothing that can be salvaged if they do agree on the objects being lock-free, fine if they do agree on the objects not being lock-free, well then explicit locking is faster anyways and you should use your "locked" reference implementation of the data structure that you surely wrote to run suitable regression tests of your lock-free data structure > > 2. What is wrong with implementing boost::interprocess::atomic<T> that > > specializes to boost::atomic<T> when possible and uses an interprocess > > lock otherwise? > > will you provide an implementation? people were asking for > boost::interprocess support during the boost.lockfree review. the only > missing feature is the atomic<> implementation. no problem Best regards Helge

1 0

[config] clang.hpp is not up-to-date
by Michel Morin 01 Nov '11

01 Nov '11

boost/config/compiler/clang.hpp is not up-to-date. For example, BOOST_NO_AUTO_DECLARATIONS is *always* defined (even if clang supports this feature). Is it worth fixing this on the release branch? P.S. I can make a patch, but before doing that I'd like to confirm whether __has_feature(cxx_auto_type) means that multi-declarator auto is supported or not. The following page says nothing about multi-declarator auto. http://clang.llvm.org/docs/LanguageExtensions.html Doug? Regards, Michel

3 4