April 2008 - Boost - lists.boost.org

Mac OS universal builds: testers needed
by Mat Marcus 25 Jul '08

25 Jul '08

I've made a number of changes to my universal-binary supporting darwin.jam patch (shipping with the Adobe Source Library) in order to address the concerns raised by Rene and others at http://svn.boost.org/trac/boost/ticket/989 : My current version supports invocations like: bjam architecture={combined,x86,power} link={shared,static} address-model={64,32} That is, universal builds are now supported, along with 64 bit builds. I'd like to ask for the help from a few volunteers who'd be willing to test it out, before I submit my patch for consideration. Anyone interested in helping me test it? If so, please contact me off list and I'll send you a couple of boost build files to replace. I still have a bit of cleanup to do. Specifically, on the mac, if a build doesn't specify an -arch parameter, the architecture (and perhaps the address model) of the host machine is used. I'm not really comfortable with the same folder path meaning different things on different machines. So, I plan to do something like the following in darwin.jam (in invented pseudo code) SWITCH(on result of /usr/bin/arch) { # host machine's architecture CASE(ppc) use <architecture>power/<address-model>32 as the default CASE(i386) use <architecture>x86/<address-model>32 as the default CASE(ppc64) use <architecture>power/<address-model>64 as the default CASE(x86_64) use <architecture>x86/<address-model>64 as the default DEFAULT error, unknown arch Thanks, Mat

3 2

[dynamic_bitset] bug in to_ulong() in dynamic_bitset.hpp
by Boris Gubenko 05 Jul '08

05 Jul '08

A failure of dynamic_bitset library test dyn_bitset_unit_tests3 on Tru64/cxx and HP-UX/aCC revealed what appears to be a bug in <boost/dynamic_bitset/dynamic_bitset.hpp> introduced after Boost 1.34. The bug affects platforms where 'long' type is larger than 'int'. On both Tru64 and HP-UX, 'int' is a 32-bit type. On Tru64, 'long' is a 64-bit type. On HP-UX, 'long' is a 64-bit type in 64-bit data model (+DD64, which is how Boost testing is done on this platform) and 32-bit type otherwise. The test also fails on other platforms and while I cannot verify it, from the test output it apears that these platforms are affected by the same bug. What fails is the two testcases below in b.to_long() suite in boost/libs/dynamic_bitset/dyn_bitset_unit_tests3.cpp invoked with run_test_cases<unsigned int>() : { std::string str(ul_width - 1, '1'); boost::dynamic_bitset<Block> b(str); Tests::to_ulong(b); } { std::string ul_str(ul_width, '1'); boost::dynamic_bitset<Block> b(ul_str); Tests::to_ulong(b); } The code in <boost/libs/dynamic_bitset/bitset_test.hpp> converts dynamic_bitset<unsigned int> argument to unsigned long and checks that the appropriate bits in the result are set: result_type num = lhs.to_ulong(); // Be sure the number is right if (sz == 0) BOOST_CHECK(num == 0); else { for (std::size_t i = 0; i < sz; ++i) BOOST_CHECK(lhs[i] == (i < n ? nth_bit(num, i) : 0)); } This check fails for the bits in the upper half of the result. Here is an excerpt from dynamic_bitset<Block, Allocator>::to_ulong() function in <boost/dynamic_bitset/dynamic_bitset.hpp> in the trunk: result_type result = 0; for (size_type i = 0; i <= last_block; ++i) { assert((size_type)bits_per_block * i < (size_type)ulong_width); result |= (m_bits[i] << (bits_per_block * i)); } In our case, last_block = 1 and bits_per_block = 32. m_bits[i] has 'unsigned int' type. On the second loop iteration, a 32-bit integer is left-shifted by 32 bit positions. This triggers undefined behaviour. From 5.8 - Shift operators [expr.shift] : "The behavior is undefined if the right operand is [...] greater than or equal to the length in bits of the promoted left operand." With cxx and aCC, such shift results in zeroing of all bits of the left operand. Here is the code from <boost/dynamic_bitset/dynamic_bitset.hpp> in Boost 1.34 : unsigned long result = 0; for (size_type i = 0; i <= last_block; ++i) { assert((size_type)bits_per_block * i < (size_type)ulong_width); // gps unsigned long piece = m_bits[i]; result |= (piece << (bits_per_block * i)); } Here on the second loop iteration, a 64-bit long is left-shifted by 32 bit positions which yields the intended result. x.cpp below illustrates the difference between trunk and Boost 1.34: x.cpp ----- #include <stdio.h> #include <limits.h> int main() { unsigned int m_bits[] = { UINT_MAX, UINT_MAX }; unsigned int bits_per_block = sizeof(int) * CHAR_BIT; unsigned long result = 0; for(int i = 0; i <= 1 ; ++i) { #ifndef Boost_1_34 result |= (m_bits[i] << (bits_per_block * i)); #else unsigned long piece = m_bits[i]; result |= (piece << (bits_per_block * i)); #endif printf("result = %llx\n", result); } } cxxosf.zko.hp.com> cxx x.cpp && a.out result = ffffffff result = ffffffff cxxosf.zko.hp.com> cxx x.cpp -DBoost_1_34 && a.out result = ffffffff result = ffffffffffffffff cxxosf.zko.hp.com> Replacing result |= (m_bits[i] << (bits_per_block * i)); with unsigned long piece = m_bits[i]; result |= (piece << (bits_per_block * i)); on the trunk makes the test succeed: verified on Tru64/cxx and on HP-UX/aCC. In <http://lists.boost.org/Archives/boost/2007/12/131126.php> I said: > It looks like a regression in boost/dynamic_bitset/dynamic_bitset.hpp > introduced in 1.35, but even in 1.34.1, it seems to me that the code in > to_ulong() is relying on undefined behaviour. What I was referring to is the code in 1.34 applying bitwise shift operator to a long operand. It would trigger an undefined behavior in C where "The operands shall have integer type", but it is legal in C++ where "The operands shall be of integral or enumeration type". So, I no longer claim that the code in 1.34 is relying on undefined behaviour. And the last thing: why the bug affects only platforms where 'long' type is larger than 'int'? Because if they are the same, as is the case on VMS or HP-UX in 32-bit data model, last_block = 0 and the single iteration of the for loop just assigns m_bits[0] to the result: the right operand of the shift operator is zero. To fix the problem, I suggest to replace the buggy code in <boost/dynamic_bitset/dynamic_bitset.hpp> in the trunk with that in 1.34. If there are no objections, I can do it. Thanks, Boris

3 3

libs/dynamic_bitset/bitset_test unmerged changes?
by David Abrahams 05 Jul '08

05 Jul '08

Should these be in the trunk? Index: bitset_test.hpp =================================================================== --- bitset_test.hpp (revision 40672) +++ bitset_test.hpp (working copy) @@ -1006,7 +1006,8 @@ bool did_throw = false; try { - s << b; + static_cast<void> + (s << b); } #if defined BOOST_OLD_IOSTREAMS catch(...) { @@ -1081,7 +1082,8 @@ const std::ios::iostate except = is.exceptions(); bool has_stream_exceptions = true; try { - is >> b; + static_cast<void> + (is >> b); } catch(const std::ios::failure &) { did_throw = true; -- Dave Abrahams Boost Consulting http://www.boost-consulting.com

2 1

boost::result_of and C++03
by Eric Niebler 30 Jun '08

30 Jun '08

My experience developing Proto has taught me a hard lesson about the ResultOf protocol that I thought I would share. Maybe someone here can tell me if/where I've gone wrong. There's a part of Proto (proto::call<>) that takes function objects, passes arguments to them and returns the result. I use result_of to compute the return type. Fine. Proto defines a function object, make_foo, whose behavior depends on the lvalue/rvalue-ness of its arguments. So for instance: // Return type of make_foo when passed a rvalue // int and an lvalue float: result_of< make_foo( int, float & ) >::type Like a good citizen, I've written make_foo's function call operator to recognize reference_wrapped and non-const-ref arguments as representing lvalues and all others as rvalues. (This is because C++03 doesn't have rvalue references.) Fine. Now, given some function type F (which may or may not be make_foo) and some arguments a0...an (which may or may not be lvalues), how do I invoke F? The strictly correct thing to do would be to wrap lvalues in reference_wrappers before passing them to F. If I don't, make_foo will do the wrong thing. However, Proto needs to work with function objects in the wild, very few of which do the right thing with reference_wrapped arguments, in my experience. What to do? I don't know. This business of needing to reference_wrap objects to get correct lvalue/rvalue semantics is a deal-breaker for Proto transforms. If I needed to wrap each lvalue argument before forwarding it to the next transform, and unpack each argument within each tranform, it would: a) Make writing transforms extremely tedious. b) Kill compile times with lots of unnecessary mpl::if_, is_reference, reference_wrapper and unwrap_reference instantiations. For these reasons, I've decided that Proto's transforms will use a different function object protocol. None of that will be visible from the outside. Transforms will still look like TR1-style function objects. But transforms will provide a separate interface for internal consumption that doesn't have this rvalue/lvalue problem. The problem, as I see it, stems from the fact that the return type calculation is separated from the function invocation. struct blarg { template<typename This, typename Arg> struct result< This( Arg ) > { // OK, if Arg is a reference, then it's an lvalue! }; template<typename Arg> typename result< make_foo( ??? ) >::type operator()( Arg const & arg ) { // whoops, I don't know here if arg is an lvalue or rvalue } }; If function objects were instead written like this ... struct blarg { template<typename Arg> struct impl { // OK, if Arg is a reference, it's an lvalue typedef ... result_type; result_type operator()(typename add_const_ref<Arg>::type arg) { // The right thing can happen here. } }; }; ... the problem goes away. -- Eric Niebler Boost Consulting www.boost-consulting.com

13 65

uniform_real: min_arg < max_arg
by Neal Becker 17 Jun '08

17 Jun '08

Can we please change assert(min_arg < max_arg); to assert (min_arg <= max_arg) ? Otherwise, breaks on corner case.

2 3

CORBA iimplementation for Boost interest?
by Jonathan Biggar 13 Jun '08

13 Jun '08

I've been working on a C++ CORBA implementation for a long time. I've considered making it open source in the past, but I hadn't seen the exact niche for it to fill. Now that Boost 1.35 is out, including ASIO and the new Threads implementation, I'm considering retargeting my implementation to only use boost libraries for underlying services. I'd be quite happy to contribute my implementation to boost, if there's enough interest for me to proceed. So, what do you all think? -- Jon Biggar Floorboard Software jon(a)floorboard.com jon(a)biggar.org

11 55

[filesystem] Problems with wpath on Linux
by Alexei Alexandrov 06 Jun '08

06 Jun '08

Hi, I'm trying to use fs::wpath on Linux and I'm encountering some problems with internal conversion of wide strings to external representation. The problem can be demonstrated with the following code: #include <iostream> #include <boost/filesystem/path.hpp> #include <boost/filesystem/convenience.hpp> namespace fs = boost::filesystem; int main() { // Setting the global locale to be environment locale std::locale::global(std::locale("")); // Setting the wpath locale to be global fs::wpath_traits::imbue(std::locale()); fs::wpath mypath(L"/tmp/some/directory"); fs::create_directories(mypath); } To me, this work looks correct and should work. But it terminates with the following message: terminate called after throwing an instance of 'boost::filesystem::basic_filesystem_error< boost::filesystem::basic_path<std::basic_string<wchar_t, std::char_traits<wchar_t>, std::allocator<wchar_t> >, boost::filesystem::wpath_traits> >' what(): boost::filesystem::wpath::to_external conversion error Aborted At the same time, the following code works: #include <iostream> #include <boost/filesystem/path.hpp> #include <boost/filesystem/convenience.hpp> #include <libs/filesystem/src/utf8_codecvt_facet.hpp> namespace fs = boost::filesystem; int main() { fs::detail::utf8_codecvt_facet utf8_facet; std::locale loc( std::locale(), &utf8_facet ); fs::wpath_traits::imbue( loc ); fs::wpath mypath(L"/tmp/some/directory"); fs::create_directories(mypath); } which uses a UTF-8 facet from boost itself. The first example should work too - this is my understanding. Who is wrong here - me or boost?

7 23

backwards compatibility
by Steve M. Robbins 03 Jun '08

03 Jun '08

Hello, I realize that Boost doesn't promise ABI compatibility across releases, nor even API compatibility according to the FAQ: How can the Boost libraries be used successfully for important projects? Many of the Boost libraries are actively maintained and improved, so **backward compatibility with prior version isn't always possible**. Deal with this by freezing the version of the Boost libraries used by your project. Only upgrade at points in your project's life cycle where a bit of change will not cause problems. Individual bug fixes can always be obtained from the boost repository. (emphasis mine) OK, but *in practice* is there a large amount of work adapting existing client code to a new release? I'm asking in order to gauge whether it is useful for a linux distribution (Debian) to keep multiple versions of Boost available simultaneously; e.g. 1.34.1 and 1.35. Currently Debian provides only the latest version of Boost. Thanks, -Steve

6 7

[thread] is there an interestoin a static thread group?
by vicente.botet 31 May '08

31 May '08

Hi, The Boost.Thread library provides a thread_group class for a collection of threads that are related in some fashion. This collection is dynamic, i.e. we can add and remove threads to this collection. When this collection is known at the group creation and can not change a static thread group could be useful. This template class thread_tuple_n will have the same operations than a thread_group, join_all, interrupt_all and size and could be used as follows: void free_function() { // .... } class X { public: void mf() { // .... } }; class Y { public: void operator()() { // .... } }; X x; Y y; thread_tuple_3 tt(free_function, make_pair(&X::mf, x), y); // ... tt.interrupt_all(); // ... tt.join_all(); Best _____________________ Vicente Juan Botet Escriba

1 1

Review Request: future library (Gaskill version)
by Braddock Gaskill 30 May '08

30 May '08

I wanted to formally request a review of my Futures library. Latest Version: http://braddock.com/~braddock/future/ The library has matured greatly over the past year. It has been heavily used as a key component in a mid-sized commercial application on both Linux and Windows. Extensive unit tests and (just now) documentation have been written - in fact there are more than twice as many lines of test code and documentation than are in the library proper. The library incorporates many ideas from this list, from other prospective submissions, other languages, and from academic papers. The library does not currently use jamfiles or boostdoc (I tried I really did). It is a header-only library. The documentation is currently straight HTML, and should be very easy to translate to boostdoc if the submission looks good. NOTE - to avoid confusion, note that there is an older 2005 boost.future candidate in the vault by Thorsten Schuett that is not related to mine (although it was studied early on). Thanks, Braddock Gaskill braddock(a)braddock.com

10 100