April 2009 - Boost - lists.boost.org

[mpl]iter_fold_if Forward Backward rationale?
by Larry Evans 10 Jun '09

10 Jun '09

Why is there both a ForwardOp and BackwardOp template argument to iter_fold_if? https://svn.boost.org/trac/boost/browser/trunk/boost/mpl/iter_fold_if.hpp#L… I would have thought that only 1 was needed. Since iter_fold_if is not documented here: http://www.boost.org/doc/libs/1_38_0/libs/mpl/doc/refmanual/refmanual_toc.h… I assume it's not meant to be used by the user, but is only an implementation detail; however, it, or a variation, might be useful to implement the and_seq mentioned here: http://article.gmane.org/gmane.comp.lib.boost.devel/186204 As shown in that post, the template, while_if_then was used, and it does not require anything like both a ForwardOp and BackwardOp, it just requires the If and Then unary metafunctions. One problem I encountered with while_if_then was moving to the end of the sequence, at which time the Then metafunction couldn't be called; hence, I had to make it lazy to avoid dereferencing the end iterator. Is that somehow related to the need for BackwardOp in iter_fold_if. IOW, because iter_fold_if might reach the end iterator, it has to backup? I'm really asking because in the variadic template version of mpl, I wondering if iter_fold_if could be replaced with something like while_if_then (which may be renamed fold_if to be more consistent with other names with similar function). Any insight about the rationale for the iter_fold_if would probably save me considerable time in deciding whether it can be replaced with the proposed fold_if. -regards, Larry

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Boost.Process article: Tutorial and request for comments
by Boris Schaeling 01 Jun '09

01 Jun '09

I've written an article about Boost.Process: http://www.highscore.de/cpp/process/ I've also fixed a few bugs in Boost.Process (which is now 0.31): http://www.highscore.de/boost/process.zip And the latest source code can also be found in the sandbox: https://svn.boost.org/svn/boost/sandbox/process/ For developers not familar with Boost.Process the article is a tutorial to get more easily started. For developers familiar with Boost.Process it is a request for comments. I've been looking at the big picture finally trying to find out where and how Boost.Process should be changed and in which direction it should move to become a complete library one day. As not everyone will read the entire article here are my thoughts: 1) Boost.Process is based on a few concepts like 'process' and 'context'. While those make sense there are other concepts where I wonder if they should be dropped: * 'executable' is the executable name which in practice must be a std::string. I think the original idea was to support numerous string types. This leads to the question how to support different Unicode encodings which I think is still unanswered in the Boost community. Other libraries, eg. Boost.Interprocess, simply stick to one string type (typically std::string). * 'handle' is the underlying native file handle of a stream (file descriptor on POSIX systems, handle on Windows). The concept is based on a class in the detail namespace of Boost.Process. There is just one class and it's not meant to be used by users of the library either. Thus I'm not sure what's the benefit of having an explicit 'handle' concept at all. 2) Environment variables must be sorted on Windows but not on POSIX systems. On Windows the type environment could be a typedef for std::map and on POSIX systems for std::unordered_map. Currently it's always a typedef for std::map. Is that ok? Should it be changed? Should a macro be provided in case developers want to use different typedefs? 3) Currently Boost.Process is really only useful for creating child processes. It's not possible for example to detect and iterate over other processes on a system. I guess Boost.Process should be enhanced here. Then one day the well-known utility 'ps' on POSIX systems could be implemented in Boost C++. Any comments? 4) When a process is created the standard streams (stdin, stdout and stderr) are closed by default. Is this a good choice? If it isn't what should happen otherwise? Inherting standard streams (which is the default behavior with fork on POSIX systems)? 5) Boost.Process requires to specify an absolute path to an executable which should be started. There is a helper function which returns the absolute path for an executable name (it uses the environment variable PATH). The question is if this should be done automatically if no absolute path is given? 6) When a stream of a child process is captured Boost.Process automatically creates a pipe. As pipes don't support asynchronous operations on Windows a named pipe is required (called FIFO on POSIX systems). Currently a macro must be defined to make Boost.Process use a named pipe on Windows. It might make more sense to enable developers to choose either a pipe or a FIFO explicitly - not only on Windows but on all platforms. Any comments? 7) It's possible to capture and access streams of a child process. Those streams are derived from std::istream and std::ostream and thus only support blocking I/O operations. Currently the underlying handle has to be fetched to initialize a generic I/O object from Boost.Asio to use asynchronous I/O operations. How should the library be changed to make it easier to use asynchronous I/O? 8) There is a method wait() which makes it possible to wait for another process to exit. Currently wait() is provided by the class child though. Shouldn't it really be defined by the class process (so you can wait not only for child processes to exit)? 9) As wait() blocks an asynchronous alternative should be provided. 10) The Windows-specific classes all start with win32_ (eg. win32_child). Wouldn't it make more sense to use windows_ instead (like windows_child) or a windows namespace? First other libraries use windows_ (see Boost.Interprocess). Second there should be no reason why a class like win32_child can't be used on a 64-bit Windows. Boris

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[1.39.0] Ready for beta?
by Beman Dawes 29 May '09

29 May '09

I've gotten badly sidetracked by non-Boost work, but would like to get the 1.39.0 beta out tomorrow if at all possible. Are there any known showstoppers? If anyone has a few spare minutes, it would help if they could download one of the current release snapshots from http://boost.cowic.de/rc/, browse around and report any problems spotted. Library authors who use Boostbook/Quickbook, but don't have time to look at the full snapshot, might want to check http://boost.cowic.de/rc/boost-docs.7z Known problems/questions: * index.html ??? needs to be replaced by new library count. * pdf docs: Do we want to do anything more for this release? Thanks, --Beman

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request for interest in a garbage collection library
by Achilleas Margaritis 29 May '09

29 May '09

Hi, I have placed in boost vault a garbage collection library: http://www.boostpro.com/vault/index.php?action=downloadfile&filename=gc.zip… The major features of this library are: 1) it supports threads; a thread can allocate gc objects and send them to other threads. 2) it is 100% portable c++; only boost and stl are used. 3) gc pointers can point to middle of objects and arrays. 4) block allocation and finalization are customizable. The collector does not do any allocation actually, it only manages blocks. 5) the collector uses the classic mark & sweep algorithm. 6) it has good (or not that bad :-)) performance. On my test machine (a dual core Pentium at 2.5 GHz with 2 GB ram), 50000 objects out of 100000 are swept in 63 milliseconds. Of course, this is due to boost::pool :-). 7) it works with STL containers (the 'how' is described in the readme). The zip file contains a set of unit tests, the API documentation and a readme file which explains the inner workings and the design of the collector. I would appreciate it if people could take a look and share their opinions on it. Best regards Achilleas Margaritis

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[gsoc] Official list released
by troy d. straszheim 29 May '09

29 May '09

On behalf of the panel of mentors, congratulations to the students listed here: http://socghop.appspot.com/org/home/google/gsoc2009/boost And a sincere thank you to all those who applied. There are a large number of entirely worthy proposals that we received that are not on that list. We had about 75 proposals, 11 willing mentors, and as you can see, Google gave us seven slots. It was very difficult to narrow down the list to these seven, and if we'd been given more slots, of course more of you would be on that list. Unfortunately, due to the sheer number of submissions and various, ahem, technical problems, it would not have been (and will not now be) possible to offer specific feedback on submissions that didn't make the cut. For this we apologize. Accepted students should eventually receive email from Google with further instructions. Per the schedule, the "community bonding" period now begins, time to get your dev. environment set up, get to know the toolchain, write some 'hello world' quickbook docs, etc. Ask for help if you need it. You can also visit some of your fellow summer coders on #boost-soc on freenode. -t

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[fusion] adding infinite sequences to fusion
by Stjepan Rajko 29 May '09

29 May '09

Hi all, There's been some off-list discussion between Dan Marsden, Joel de Guzman and myself on how to address infinite sequences in fusion. Joel suggested to bring the discussion back to the list for more feedback: On Wed, Apr 15, 2009 at 6:21 PM, Joel de Guzman <djowel(a)gmail.com> wrote: > Stjepan Rajko wrote: >> >> Here is a list and description of all of the concepts that might be >> relevant: >> >> >> Forward Sequence >> begin(s) - returns a Forward Iterator >> empty(s) - returns a bool >> front(s) - any type >> >> Finite Forward Sequence >> refines Forward Sequence >> end(s) - returns a Forward Iterator >> size(s) - MPL integral constant >> >> Infinite Forward Sequence >> refines Forward Sequence >> empty(s) - returns false >> size(s) - infinity >> >> Bidirectional Sequence >> refines Forward Sequence >> begin(s) - returns a Bidirectional Iterator >> >> Finite Bidirectional Sequence >> refines Bidirectional Sequence, Finite Forward Sequence >> end(s) - returns a Bidirectional Iterator >> back(s) - any type >> >> Infinite Bidirectional Sequence >> refines Bidirectional Sequence, Infinite Forward Sequence >> >> Random Access Sequence >> refines Bidirectional Sequence >> begin(s) - returns a Random Access Iterator >> >> Finite Random Access Sequence >> refines Random Access Sequence, Finite Bidirectional Sequence >> end(s) - returns a Random Access Iterator >> >> Infinite Random Access Sequence >> refines Random Access Sequence, Infinite Bidirectional Sequence >> >> >> How does that look? > > I'd suggest posting that to the Boost list to get more feedback. > I have a feeling that infinity is a separate concept orthogonal > to traversal. But I'm not sure. > The above layout is almost orthogonal, with Infinite Forward Sequence and Finite Forward Sequence serving as "base" concepts related to Finite / Infinite. I suppose you could have less refined Infinite Sequence and Finite Sequence concepts, but I'm not sure how useful they would be (AFAICT, they could only describe `size` and `empty`). Things aren't perfectly orthogonal because Finite + Bidirectional require `back`, but Finite + Forward do not, and neither do Infinite + Bidirectional. Best, Stjepan > Regards, > -- > Joel de Guzman > http://www.boostpro.com > http://spirit.sf.net >

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G++ hack/challenge?
by David Abrahams 27 May '09

27 May '09

Hi all, In preparation for BoostCon, I'm looking for a workaround for the problems described in http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2855.html. In particular I need a way to detect whether a type "has a move constructor" (without causing a compiler error, of course) in GCC 4.4. Ideally, "has a move constructor" would mean - when constructed from an rvalue of the same type, a copy constructor with signature T(T const&) is not used. though I would settle for - has a constructor with the signature T(T&&) I'm willing to use G++-specific hackery if necessary. I strongly suspect it's impossible, but if you can think of any way to do it, I'd really appreciate knowing about it. You'll be my hero forever ;-) TIA, -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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git clone up
by troy d. straszheim 18 May '09

18 May '09

In case this reaches any other git enthusiasts, I've rigged up a git clone that is automatically tracking boost svn, here: http://sodium.resophonic.com/git/boost/ Click around on it... it's smoking fast, despite the fact that it is running on hardware I found in the trash on the end of a mediocre uplink. There is a little howto here: http://sodium.resophonic.com/git/boost/about/ The repository (minus checkout) is about 150M, it contains branches and tags going all the way back. It will take a while to do the initial clone but fetches after that are very fast. -t

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[test] Using the Boost Unit Test Framework with shared libs
by Peter 17 May '09

17 May '09

Hi I am using Boost.Test from the current boost 1.38 , on cygwin ( gcc ) and I want to use it with multiple test files and with shared libs ( in order to speed up the compilation time which is too long for me when using the header include variant ). What is the recommended way ? ( I read the doc, several times and I read the _long_ threads on the mailing list concerning the static/shared library issue, but I am not sure that I understood all the details). I did the following: *in mainTest.cpp:* #define BOOST_TEST_DYN_LINK #define BOOST_TEST_MAIN #include "../inc/globalFixture.hpp" #include "../inc/testfile1.hpp" #include "../inc/testfile2.hpp" *testfile1.hpp:* #include "globalFixture.hpp" BOOST_FIXTURE_TEST_SUITE(ATlib1, Fixture) BOOST_AUTO_TEST_CASE(Resource_Manager) { ... ....BOOST_CHECK .... } BOOST_AUTO_TEST_SUITE_END() *testfile2.hpp:* #include "globalFixture.hpp" BOOST_FIXTURE_TEST_SUITE(ATlib2, Fixture) BOOST_AUTO_TEST_CASE(FileManager { ... BOOST_CHECK .... } BOOST_AUTO_TEST_SUITE_END() *globalfixture.hpp: *#ifndef _GLOBALFIXTURE_HPP #define _GLOBALFIXTURE_HPP #define BOOST_TEST_MODULE ATlib #include <iostream> #include <boost/test/unit_test.hpp> #include <boost/test/detail/unit_test_parameters.hpp> #include <boost/bind.hpp> #include <boost/test/output_test_stream.hpp> using namespace boost::unit_test; struct GlobalConfig { GlobalConfig() { std::cout << "GlobalConfig setup\n"; using namespace boost::unit_test; if (runtime_config::log_level() < log_warnings) unit_test_log.set_threshold_level(log_successful_tests); }; ~GlobalConfig() { std::cout << "GlobalConfig teardown\n"; } }; BOOST_GLOBAL_FIXTURE(GlobalConfig); struct Fixture { Fixture() { BOOST_TEST_MESSAGE("setup Fixture"); using namespace boost::unit_test; unit_test_log.set_threshold_level(log_successful_tests); } ~Fixture() { BOOST_TEST_MESSAGE("teardown Fixture"); } }; #endif /* _GLOBALFIXTURE_HPP */* *I then link to boost_unit_test_framework-gcc34-mt-1_38.so The link passes , but I get a warning from gcc++ 3.4.4 that auto-linking has been enabled ( I will provide the exact details if useful ). I can execute the resulting mainTest.exe without problems, but the compiler warnings tells that something is not quite right. Is the above example the right way to use multiple test files ? Are the flags for shared libs correctly set ? Thanks for your help. PS: I think that Boost.Test is not easy to grasp ( at least for me ). I think this is partially due to a lack of complete examples ( involving for examples a test suite with more than one test file ). Also the static/shared library topic and the related macros ( BOOST_TEST_DYN_LINK etc ) could do with a concrete example. Maybe the mentioned case above could serve as an example after clarification. Peter

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[New Feature Suggestion] Dynamic exception handlers registration
by Alex Tkachenko 17 May '09

17 May '09

Hello there. A while back I wrote usefull tool for organizing exception handling. The general idea is borrowed from boost::execution_monitor (http://www.boost.org/doc/libs/1_38_0/libs/test/doc/html/execution-monitor.h…) . Similarly, I call this unit "Exception Monitor". It allows to dynamically register exception converters and convert exception objects from any source types to arbitrary target type. For instance, if you write some integration code which uses several external modules, and each of these modules could generate their own tree of exceptions, you would face serious issue trying to implement error diagnostic. One approach is to handle only base exception for each module and to catch them in function main(). Let's assume that all exceptions are inherited from std::exception, so we need to catch single base (std::exception). This approach is convenient but not precise. Even if we want just to output error message using std::exception::what() we have only some general low level error description, moreover this description could be completely wrong. It doesn't reflect actual cause of the error because at the place where the exception is originally generated it couldn't know about context of execution. On the contrary, we can catch low-level exceptions in the place where execution context is more obvious and convert it to some "application" exception which contains more information about current situation. This is the solution for detailed error diagnostic, but it is too tedious. Also such code is unscalable, error prone and hard to support. Look at the following example: /////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////// class app_error: public virtual std::exception { ... }; void foo() { try { ...local state... unit1::foo(...); unit2::foo(...); } catch(const unit1::exception1& ex) { //...convert caught exception to app_error using local state throw app_error(...); } catch(const unit1::exception2& ex) { //...convert caught exception to app_error using local state throw app_error(...); } catch(const unit2::exception& ex) { //...convert caught exception to app_error using local state throw app_error(...); } } int main() { try { foo(); } catch(const app_error& ex) { cout << "Error: " << ex.what() << endl; } catch(const std::exception& ex) { cout << "Unknown error: " << ex.what() << endl; } catch(...) { cout << "Unknown error" << endl; } } The main drawback of this source code is that exception handling is mixed with 'main' code. It would be better if we could write something like this: /////////////////////////////////////////////////////////// /////////////////////////////////////////////////////////// class app_error: public virtual std::exception { ... }; typedef exc::catcher<app_error> app_catcher; //...exception catcher type typedef std::list<app_catcher> app_catchers; //...container for catchers struct convert_unit1_ex1 { const app_error operator()(const unit1::exception1&); }; struct convert_unit1_ex2 { const app_error operator()(const unit1::exception2&); }; struct convert_unit2_ex { const app_error operator()(const unit2::exception&); }; app_catchers excon; void foo() { ...local state... //...register catchers for possible exceptions excon.push_front( app_catcher::create<unit1::exception1>( convert_unit1_ex1(...local state...))); excon.push_front( app_catcher::create<unit1::exception2>( convert_unit1_ex2(...local state...))); excon.push_front( app_catcher::create<unit2::exception>( convert_unit2_ex(...local state...))); //... unit1::foo(); unit2::foo(); //...good idea is to use RAII to register catchers to avoid this //...manual deregistration: excon.pop_front(); excon.pop_front(); excon.pop_front(); } int main() { try { guard(excon, foo()); } catch(const app_error& ex) { cout << "Error: " << ex.what() << endl; } catch(const std::exception& ex) { cout << "Unknown error: " << ex.what() << endl; } catch(...) { cout << "Unknown error" << endl; } } Pluses of this technique: 1) it encourages developer to implement exception handlers code separatly from 'main' code; 2) it provides framework for detailed exception handling; 3) it offers flexible means for structural arrangement of exception handlers' source code. Very interesting feature of Exception Monitor is ability to sort catchers in "proper" order regarding their inheritance. So catcher for std::runtime_error should be earlier then std::exception. This is what functions exc::insert and exc::replace do. Library source code (it's tested it on gcc 4.3.1): #ifndef EXCEPTION_MONITOR_HEADER_GUARD #define EXCEPTION_MONITOR_HEADER_GUARD /* * Exception Monitor: * allowes dynamic exception handlers registration * Author: Alex Tkachenko * 2009.02.10 */ #include <cassert> #include <boost/function.hpp> #include <boost/static_assert.hpp> #include <boost/type_traits/is_base_of.hpp> #include <boost/shared_ptr.hpp> #include <typeinfo> namespace exc { namespace details { class failed_to_catch_exception {}; //... class try_catcher_base { public: virtual ~try_catcher_base() {} virtual void convert() const = 0; virtual void try_throw_self_exception() const = 0; virtual bool try_catch_self_exception( const try_catcher_base& other) const = 0; virtual const std::type_info& type() const = 0; }; template<typename Texception_to, typename Texception_from> class try_catcher: public try_catcher_base { typedef boost::function<const Texception_to (const Texception_from&)> converter_f; public: try_catcher(const converter_f& iconverter): converter(iconverter) { assert(!converter.empty() && "Null converter"); } private: void convert() const { try { throw; } catch(const Texception_from& ex) { throw converter(ex); } catch(...) { throw failed_to_catch_exception(); } } void try_throw_self_exception() const { throw (Texception_from*)0; } bool try_catch_self_exception(const try_catcher_base& other) const { try { other.try_throw_self_exception(); } catch(Texception_from*) { return true; } catch(...) { return false; } } const std::type_info& type() const { return typeid(Texception_from); } //... converter_f converter; }; }//...namespace details template<typename Texception_to> class catcher { typedef boost::shared_ptr<details::try_catcher_base> impl_t; catcher(const impl_t& iimpl): impl(iimpl) { assert(impl && "NULL catcher implementation"); } void convert() const { impl->convert(); } void try_throw_self_exception() const { impl->try_throw_self_exception(); } bool try_catch_self_exception(const catcher& other) const { return impl->try_catch_self_exception(*other.impl); } public: typedef Texception_to Texception_to_type; template<typename Texception_from> static const catcher create( const boost::function<const Texception_to (const Texception_from&)> converter) { //...it's senseless to convert from derived to base exception, //...or convert exception to its own type BOOST_STATIC_ASSERT( (!boost::is_base_of<Texception_to, Texception_from>::value)); return catcher( impl_t( new details::try_catcher<Texception_to, Texception_from>( converter))); } //... const std::type_info& type() const { return impl->type(); } void swap(catcher& rhs) { impl.swap(rhs.impl); } private: template<typename Treturn, typename Tcatchers> friend Treturn guard( const Tcatchers& catchers, const boost::function<Treturn ()>& func); template<typename TcatchersIterator> friend TcatchersIterator find( TcatchersIterator begin, TcatchersIterator end, const typename std::iterator_traits<TcatchersIterator>::value_type& catcher); //... impl_t impl; }; template<typename Treturn, typename Tcatchers> Treturn guard( const Tcatchers& catchers, const boost::function<Treturn ()>& func) { assert(!func.empty() && "Empty function"); typedef typename Tcatchers::value_type::Texception_to_type Texception_to_type; try { return func(); } catch(...) { const typename Tcatchers::const_iterator end(catchers.end()); for(typename Tcatchers::const_iterator iter(catchers.begin()); end != iter; ++iter) { try { iter->convert(); } catch(const Texception_to_type&) { throw; } catch(details::failed_to_catch_exception) { //...try next handler } } throw; } } template<typename Tcatchers> inline void guard( const Tcatchers& catchers, const boost::function<void ()>& func) { guard<void, Tcatchers>(catchers, func); } template<typename Texception_to> inline bool operator==( const catcher<Texception_to>& lhs, const catcher<Texception_to>& rhs) { return lhs.type() == rhs.type(); } template<typename Texception_to> inline bool operator!=( const catcher<Texception_to>& lhs, const catcher<Texception_to>& rhs) { return !(lhs == rhs); } template<typename Texception_to> inline void swap(catcher<Texception_to>& lhs, catcher<Texception_to>& rhs) { lhs.swap(rhs); } template<typename TcatchersIterator> TcatchersIterator find( TcatchersIterator begin, TcatchersIterator end, const typename std::iterator_traits<TcatchersIterator>::value_type& catcher) { for(;end != begin; ++begin) if(begin->try_catch_self_exception(catcher)) return begin; return end; } template<typename Tcatchers> void insert(Tcatchers& catchers, const typename Tcatchers::value_type& catcher) { typename Tcatchers::iterator iter( exc::find(catchers.begin(), catchers.end(), catcher)); catchers.insert(iter, catcher); } template<typename Tcatchers> void replace(Tcatchers& catchers, const typename Tcatchers::value_type& catcher) { typename Tcatchers::iterator iter( exc::find(catchers.begin(), catchers.end(), catcher)); if(catchers.end() == iter) catchers.push_back(catcher); else if(catcher == *iter) *iter = catcher; else catchers.insert(iter, catcher); } } //...namespace exc #endif /*EXCEPTION_MONITOR_HEADER_GUARD*/

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