December 2009 - Boost - lists.preview.boost.org

[Review Results] Boost.Polygon library accepted into boost
by Fernando Cacciola 07 Apr '10

07 Apr '10

Dear Boosters, [first of all allow me to apology for not doing this before. My small consulting bussines suddenly grew out of proportion and now is way over my head, keeping me working/managing 16 hours a day] I am pleased to announce that the Boost.Polygon library from Lucanus Simonson has been accepted into boost provided some of the most critical concerns, detailed below, are addressed first. First of all I would like to thank Lucanus and Intel Corporation for making this work available to all C++ developers around the world. I would also like to thank all the reviewers that participated (in no particular order nor degree of participation) Thomas Klimpel Frank Mori Hess Barend Gehrels Andreas Fabri Jeffrey Hellrung Tim Keitt Markus Werle Paul A. Bristow Robert Stewart Mathias Gaunard Michael Fawcett Steven Watanabe Joachim Faulhaber John Bytheway Sebastian Redl Mika Heiskanen John Phillips Kai Benndorf Hartmut Kaiser Arash Partow Maurizio Vitale Brandon Kohn David Abrahams Gordon Woodhull Daniel James John Maddock Tom Brinkman Bo Persson Mateusz Loskot Christian Henning Jean-Sebastien Stoezel The library had 6 yes votes and 4 no votes. Those who voted no made the following major complains and remarks (they are numbered as I will refer to them back later): Barend Gehrels: (1) According to his benchmarks, intersection algorithms are unnecesarily slow as if something where fundamentally wrong in the design and/or implementation. AFAICT the implication has not been proved or disproved so far, hence I consider it a red herring and cannot take it as a reason for rejecting the library, but it is important to look at it in detail. (2) As a major complain, the library is unusable in those domains where floating point support is a requirement (like GIS). (3) The library should contain some basic polygon geometry algorithms such as convex hull and centriod Phil Endecott: (4) There is no concept checking in the code so it is difficult to adapt. (5) There where too many warnings and build errors (but Luke fixed these) (6a) The documentation needs a better overview of operations supported by the concetps. (6b) It also needs the details on the algorithms complexities. (6c) It also misses the numerical requirements for the coordinate type. (6d) And tutorials. (7) Some operators are ambiguous and it would be better to keep just one of each "flavor". (8) The polygon_data template class is parameterized by a coordiante type rather than a point type. This makes it useless for integration with existing geometric data types Michael Fawcett: (5), (6a), (6d) (9) T9he API should provide versions using output iterators in addition to output container references. (10) Theoreticall the library would be usable with a user defined coordinate type (metting certain requirements now undocumented), for example a fixed point data type, but some details in the internal design and implementation prevents this. (11) As a major complain, the library is unusable in those domains where floating point support is a requirement (like GIS). Hartmut Kaiser: (11), (1) Fernando Cacciola: (12) The name of the library should change to better indicate that is restricted to Integral coordinates and two-dimensions. (13) The documentation must contain a "credits" section acknowledging all the people that participated in the review. For the library to be effectively accepted, points (5),(6a-d),(10), (12) and (13) should properly addressed ((5) is already done AFAICT) It would be quite significant if point (1) where looked into. Once again I thank Lucanus, Intel Corporation and all the reviwers. Best regards -- Fernando Cacciola SciSoft Consulting, Founder http://www.scisoft-consulting.com

4 4

Trac XMLRPC support
by Vladimir Prus 21 Mar '10

21 Mar '10

Would it be possible to have XMLRPC plugin installed in Boost Trac instance? See: http://trac-hacks.org/wiki/XmlRpcPlugin The installation appears to be fairly simple (and indeed seems to just work somewhere else). This will allow to use third-party tools to grab tickets from Boost Trac, which will hopefully lead to more issues fixed :-) - Volodya

4 5

[unordered] unordered_set::erase() complexity bug?
by Stefan Strasser 18 Mar '10

18 Mar '10

I think there is something very wrong with boost's implementation of unordered_set/map. 1 unordered_set<int> s; 2 for(int c=0;c<nr;++c) s.insert(c); 3 for(int c=nr-1;c>=0;--c) s.erase(s.find(c)); results: nr: time 20000: 0m0.244s 40000: 0m0.940s 60000: 0m5.584s 80000: 0m4.232s 100000: 0m34.814s 120000: 0m33.486s the function that's causing this is erase(), which is specified to be O(1) average, O(n) worst. I can't think of a reason why it should be O(n) in this case (perfect hash, erase doesn't rehash). but even if it was, the results should be at worst quadratic. load_factor() is below 1, bucket_count(x) is 1. if line 3 is changed to: 3 for(int c=0;c<nr;++c) s.erase(s.find(c)); 20000: 0m0.008s 40000: 0m0.016s 60000: 0m0.028s 80000: 0m0.032s 100000: 0m0.040s 120000: 0m0.044s as you would expect. even if I do the very same thing as above using Boost.Intrusive (using a load factor of 1), I get expected results: struct element : intrusive::unordered_set_base_hook<>{ ... for(int c=0;c<nr;++c) s.insert(*new element(c)); for(int c=nr-1;c>=0;--c) s.erase(s.find(element(c))); 20000 0m0.008s 40000 0m0.016s 60000 0m0.024s 80000 0m0.024s 100000 0m0.032s 120000 0m0.040s but surprisingly enough, the TR1 implementation shipped with libstdc++ also has a problem like that: 20000: 0m0.368s 40000: 0m1.448s 60000: 0m1.668s 80000: 0m7.160s 100000: 0m7.808s 120000: 0m13.349s am I missing something or is there really the same bug in 2 major implementations of unordered_set? it effectively caused a deadlock in some of my code. I'm using 1.38. no bug report in Trac.

20 48

enable_shared_from_this2
by Berserker 09 Mar '10

09 Mar '10

After experiencing some troubles with boost::python and enable_shared_from_this (as already reported in the past by someone to Peter Dimov), I started looking at the new (not documented) class enable_shared_from_this2. I made two changes in init_weak_once and now it seems to support shared_from_this in constructors and shared pointers "reinitialization". The original code (from boost 1.40): void init_weak_once() const { if( weak_this_._empty() ) { shared_this_.reset(static_cast< T* >( 0 ), detail::esft2_deleter_wrapper()); weak_this_ = shared_this_; } } The "patched" code: void init_weak_once() const { // Reinitialization support if( weak_this_.expired() ) { // shared_from_this in costructors support shared_this_.reset(static_cast <T*>(const_cast<enable_shared_from_this2>(this)), detail::esft2_deleter_wrapper()); weak_this_ = shared_this_; } } I know that the static_cast/const_cast is "problematic" on VC6 (and maybe other compilers) but it could be solved using an offset from enable_shared_from_this2 * to T *. I've attached a testcase that shows the problems with the current enable_shared_from_this2 implementation (with the proposed patch it works). Any feedback about this? struct null_deleter { template <typename T> inline void operator()(T *p) const { } }; class EnableThisPtrTester : public boost::enable_shared_from_this2<EnableThisPtrTester> { public: EnableThisPtrTester() { } EnableThisPtrTester(shared_ptr<EnableThisPtrTester> &ptr) { ptr = shared_from_this(); BOOST_CHECK(ptr); } }; BOOST_AUTO_TEST_CASE(test_enable_this_ptr) { { shared_ptr<EnableThisPtrTester> ptr1; shared_ptr<EnableThisPtrTester> ptr2(new EnableThisPtrTester(ptr1)); BOOST_CHECK(ptr1 == ptr2); BOOST_CHECK(ptr1.use_count() == ptr2.use_count()); BOOST_CHECK(ptr1->shared_from_this() == ptr1); BOOST_CHECK(ptr1->shared_from_this().use_count() == ptr1.use_count()); shared_ptr<EnableThisPtrTester> ptr3 = ptr2->shared_from_this(); BOOST_CHECK(ptr2 == ptr3); BOOST_CHECK(ptr2.use_count() == ptr3.use_count()); BOOST_CHECK(ptr1->shared_from_this().use_count() == ptr1.use_count()); } { shared_ptr<EnableThisPtrTester> ptr1; EnableThisPtrTester tester(ptr1); shared_ptr<EnableThisPtrTester> ptr2 = tester.shared_from_this(); BOOST_CHECK(ptr1 == ptr2); BOOST_CHECK(ptr1.use_count() == ptr2.use_count()); ptr1.reset(); ptr2.reset(); } { EnableThisPtrTester tester; { shared_ptr<EnableThisPtrTester> ptr1 = tester.shared_from_this(); shared_ptr<EnableThisPtrTester> ptr2 = tester.shared_from_this(); BOOST_CHECK(ptr1 == ptr2); BOOST_CHECK(ptr1.use_count() == ptr2.use_count()); shared_ptr<EnableThisPtrTester> ptr3(&tester, null_deleter()); BOOST_CHECK(ptr1 == ptr3); BOOST_CHECK(ptr1.use_count() == ptr3.use_count()); shared_ptr<EnableThisPtrTester> ptr4 = tester.shared_from_this(); BOOST_CHECK(ptr4 == ptr1); BOOST_CHECK(ptr4 == ptr3); BOOST_CHECK(ptr1.use_count() == ptr4.use_count()); BOOST_CHECK(ptr3.use_count() == ptr4.use_count()); } BOOST_CHECK(tester.shared_from_this()); } }

7 22

boost::mpl::for_each and value_initialized
by Peter Foelsche 08 Feb '10

08 Feb '10

Dear All, what is the use of value_initialized in boost::mpl::for_each? It should be sufficient if the value is initialized by the constructor. value_initialized() calls memset() in before calling the constructor. This memset() is not being optimized away with gnu-c++ 4.4.1. What class does require zeroed memory to work correctly? Peter *** boost_1_40_0/boost/mpl/for_each.hpp Mon Aug 17 22:16:53 2009 --- boost_1_40_0.saved/boost/mpl/for_each.hpp Tue Sep 1 12:54:55 2009 *************** *** 71,78 **** // dwa 2002/9/10 -- make sure not to invoke undefined behavior // when we pass arg. ! value_initialized<arg> x; ! aux::unwrap(f, 0)(boost::get(x)); typedef typename mpl::next<Iterator>::type iter; for_each_impl<boost::is_same<iter,LastIterator>::value> --- 71,78 ---- // dwa 2002/9/10 -- make sure not to invoke undefined behavior // when we pass arg. ! //value_initialized<arg> x; ! aux::unwrap(f, 0)(arg()); typedef typename mpl::next<Iterator>::type iter; for_each_impl<boost::is_same<iter,LastIterator>::value>

5 10

[gil] trac #3619
by Christian Henning 03 Feb '10

03 Feb '10

Hi there, could someone please tell whether or not this bug still exists. I don't have access to gcc 4.4. This is marked as a showstopper and I would like to get rid of it. Is it a compiler bug maybe? Thanks, Christian

2 1

[multi_index][serialization] save_construct_data not called for multi_index collection
by Felipe Magno de Almeida 03 Feb '10

03 Feb '10

Hi, Boost.Serialization has support for non-default classes using save_construct_data and load_construct_data overloads. These are called before serialization to save and load information that's important for the construction of the object. Unfortunately, multi_index doesn't call these functions when serializing, so serialization of non-default-constructible classes is impossible with multi_index. I wanted to patch it so that it becomes possible, but to be honest I'm a bit lost in the serialization code for multi_index. collections_save_impl calls boost::serialization::save_construct_data_adl before serializing each item in the collection. I'm using boost 1.38.0, is there anyway to do the same for multi_index? Thanks in advance, -- Felipe Magno de Almeida

4 8

Boost.Atomic request for review/inclusion
by Helge Bahmann 01 Feb '10

01 Feb '10

Hello, First of all I would like to thank for the comments that I have received so far, I have incorporated almost all of them I think. Boost.Atomic is now in a form that I consider calling it a release. It has support for "true" atomic variables on: - gcc/x86, 32-bit (tested on Linux, FreeBSD) - gcc/x86, 64-bit (tested on Linux) - gcc/powerpc32 (tested on Linux, Mac OS X) - gcc/powerpc64 (untested) - generic Win32 (tested with Visual Studio Express on Win XP) For all others it falls back gracefully to locked operation. There is proper quickbook documentation, including a hopefully illustrative example section. If you have an unsupported platform, contact me and I will attempt to provide support for it (usually it is just a matter of testing). Otherwise I would like to request considering the library for inclusion and appreciate any further comments. Everything available as usual at: http://www.chaoticmind.net/~hcb/projects/boost.atomic Best regards Helge

6 12

doc for is_lvalue_iterator?
by Neal Becker 29 Jan '10

29 Jan '10

I don't see any doc for is_lvalue_iterator (and related metafunctions)

2 1

type of iterator_facade::value_type
by Neal Becker 29 Jan '10

29 Jan '10

According to iterator_facade doc: typedef remove_const<Value>::type value_type; Why remove_const? This makes it hard to detect if the resulting iterator points to a const value. In order to further adapt such an iterator, I needed to use the reference type instead of the value type to detect constness: typename boost::is_const< typename boost::remove_reference< typename std::iterator_traits<BaseIterator>::reference >::type >::type,

3 2