September 2012 - Boost - lists.boost.org

[TypeErasure] references
by Chapman, Alec 10 May '13

10 May '13

Hi Steven, I have a somewhat-generic type erasure class that I would like to switch to yours. The main difficulty I can see is in the way capturing by reference is handled. The approach I take in my class is to pass a boost::reference_wrapper to the constructor: typedef mpl::vector<copy_constructible<>, type_id_<>, incrementable<> > requirements; int i = 0; any<requirements> x(boost::ref(i)); // capture i by reference ++x; // i == 1 any<requirements> y(x); // makes a copy of i ++y; // i == 1, any_cast<int>(y) == 2 My motivation is that I have a bunch of template functions already written that I often call directly, but in other cases I need to compile them separately by instantiating them with any<...>: ---------------------- module 1 ------------------------- // some long algorithm that I don't want to modify to be aware of any<...> template<class T> void f(T& t) { ++t; T t2 = t; ++t2; // do something with t2 } // make a type-erased version for separate compilation void any_f(any<requirements>& x) { return f(x); } -------------------- module 2 ---------------------------- // provide a thin wrapper that applies type erasure before calling any_f template<class T> void f_fwd(T& t) { any<requirements> x(boost::ref(t)); any_f(x); } // some function that needs to call f void g(int& i) { // do something with i... // then pass it to f f_fwd(i); } Is something like this possible with your method? Are there advantages that I'm not seeing to having the type signature contain information about whether the object is held by reference? Thanks, Alec

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What Should we do About Boost.Test?
by Dave Abrahams 16 Apr '13

16 Apr '13

Hi All, I was just going through Boost.Test to try to figure out how to teach it, and while it looks to have substantial value, it is also in quite a mess. It contains loads of features that are exercised in the examples/ directory but neither included in any of the tests nor documented. There are facilities for command-line argument parsing! There are "decorators" that turn on/off features for test cases. There is support for mock objects! These are cool and sometimes necessary features, but who knew? The third tutorial page (http://www.boost.org/doc/libs/1_51_0/libs/test/doc/html/tutorials/new-year-…) has a glaring typo in the code examples: "BOOST_AUTO_EST_CASE". There's no reference manual at all. There are nearly-identical files in the examples/ directory called "est_example1.cpp" and "test_example1.cpp" (Did the "t" key on someone's keyboard break?) I could go on, but where would I stop? I don't know what to do about this. Because of the lack of redundancy (i.e. tests and documentation), it's hard to tell whether this library is correct or even to define what "correct" should mean. It seems like, as long as the code is incompletely / incorrectly documented and tested, it's just someone's personal coding project that we happen to keep shipping with Boost, and not really a library for general use. This situation reflects poorly on Boost as a whole and the fact that it centers around a _testing_ library, which is concerned with robustness... well, let's just say that the irony isn't lost on me. I don't mean this posting as an attack on Gennadiy in any way, but I think the situation is unacceptable and therefore am opening a discussion about what should happen. As a straw man, I'll make this suggestion: - Boost.Test is officially deprecated in the next release - Its documentation, such as it is, is removed from the release after that - Meanwhile, other tests in Boost that use this library are rewritten to use a different mechanism - The code is removed from Boost thereafter I am not at all attached to removing Boost.Test from Boost, but IMO rescuing it would require a significant new investment of time and energy from people who are committed to bringing the library up to par with the rest of what we do. (I seriously thought about volunteering for this myself, but realistically speaking, I don't have the time, and volunteering for something you can't actually do is worse than not volunteering at all.) Even if volunteers show up, I'd suggest proceeding with the plan above, subject to reversal at any time the work actually gets done. Thoughts? -- Dave Abrahams BoostPro Computing Software Development Training http://www.boostpro.com Clang/LLVM/EDG Compilers C++ Boost

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[config] consexpr workaround
by vicente.botet 21 Mar '13

21 Mar '13

Hi, in order to make easier the introduction of constexpr in a portable way I would like we add a Boost Config workarround. We can define some macros depending on whether BOOST_NO_CONSTEXPR is defined or not. #if defined(BOOST_NO_CONSTEXPR) #define BOOST_CONSTEXPR #define BOOST_CONSTEXPR_OR_CONST const #else #define BOOST_CONSTEXPR constexpr #define BOOST_CONSTEXPR_OR_CONST constexpr #endif For most of the constexpr functions or constructors BOOST_CONSTEXPR will work. constexpr tuple(); =versus= BOOST_CONSTEXPR tuple(); When used for static constants BOOST_CONSTEXPR_OR_CONST is needed as we need to preserv the const keyword when consexpr is not available. static constexpr UIntType xor_mask = a; =versus= static BOOST_CONSTEXPR_OR_CONST UIntType xor_mask = a; We could also add a STATIC_CONSTEXPR macro #define BOOST_STATIC_CONSTEXPR static BOOST_CONSTEXPR_OR_CONST static constexpr UIntType xor_mask = a; =versus= BOOST_STATIC_CONSTEXPR UIntType xor_mask = a; For this case the existing macro BOOST_STATIC_CONSTANT could be modified to use BOOST_CONSTEXPR_OR_CONST when static const was used. static constexpr UIntType xor_mask = a; =versus= BOOST_STATIC_CONSTANT(UIntType, xor_mask = a); Can we introduce this workaround? Best regards, Vicente _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/

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[thread] thread_specific_ptr leaks on VS2012 when using std::async()
by Klaim - Joël Lamotte 05 Mar '13

05 Mar '13

Hi, The title says it all. I think I found a memory leak with the help of boost.log author Andrei Semashev. I was using Boost.Log in Visual Studio 2012 (released one) and tried to use Visual Leak Detector because Visual Studio basic leak detector was reporting leaks. I isolated the leaks to usage of log and switched to VLD to check if the basic detector wasn't giving me false positive. I contacted Andrei to see if he could check it but he don't have VS2012 available so I setup some tests to isolate the problem. In the end of our exchange we concluded it was a false positive (it only leak on end of program). However it is still an annoying noise in the leak report logs, so people not understanding the source of this problem might be interested in this email. I attach the whole email exchange to this email, tell me if leak logs are necessary too. The last version of my test is at the end of the email (first program). Basically, the leak appear only when using std::async() in combination of boost::thread_specific_ptr : - using exclusively boost threading libraries (both with dynamic and static linking) result in no leak - using exclusively std threading libraries but not std::async() result in no leak - using std::async() result in a leak The second test program shows that using Intel Threading Building Blocks, I get leaks only if : - I use std::async() in combination with boost::thread_specific_ptr, as before (I mean I use tbb without a leak, then I add a std::async() call to the same task function and there is a leak) - I don't use std::async() but I don't manage the lifetime of tbb task scheduler We think the threads spawned by both tbb (that is supposed to be a superset of ppl) and std::async() (that is supposed to use ppl/concrt task scheduler) are not ended yet when the program reach the end of main (which seems logical as the task scheduler is then managed as a static global), making boost::thread_specific_ptr not release some data on thread destruction, as it is notified too late and any leak detection tool willl generate noise due to this. A way to fix this is to explicitely end the task scheduler, being tbb or ppl/concrt. I will use tbb task scheduler explicitely initialized/terminated in my project so it will solve the problem on my side. Joel Lamotte ------------------------------------ // this program was used to see the memory leak #define TEST_ASYNC // comment this to make it linear and not leak //#define WITH_BOOST_THREADS #define WITH_STD_ASYNC // uncomment this to leak //#define WITH_BOOST_LOG // boost log also leak if std::async is used #include <boost/thread.hpp> #ifdef WITH_BOOST_THREADS # include <boost/thread/future.hpp> # include <boost/chrono.hpp> # define THIS_THREAD boost::this_thread # define THREAD_LIB boost::thread # define CHRONO_LIB boost::chrono # define MY_FUTURE boost::future #else # include <future> # include <thread> # include <chrono> # define THIS_THREAD std::this_thread # define THREAD_LIB std::thread # define CHRONO_LIB std::chrono # define MY_FUTURE std::future #endif #ifdef WITH_BOOST_LOG # include <boost/log/trivial.hpp> # define MY_LOG BOOST_LOG_TRIVIAL(info) #else # include <iostream> # define MY_LOG std::cout << '\n' #endif #define BASIC_VS_LEAK_DETECTOR 0 #define VISUAL_LEAK_DETECTOR 1 #define LEAK_DETECTOR VISUAL_LEAK_DETECTOR #if LEAK_DETECTOR == BASIC_VS_LEAK_DETECTOR # define _CRTDBG_MAP_ALLOC # include <stdlib.h> # include <crtdbg.h> #else # include "vld.h" #endif struct my_data { char data[1024]; my_data() { MY_LOG << "CONSTRUCTOR my_data - " << THIS_THREAD::get_id(); } ~my_data() { MY_LOG << "DESTRUCTOR my_data - " << THIS_THREAD::get_id(); } }; boost::thread_specific_ptr< my_data > ts_ptr; void my_thread_foo() { ts_ptr.reset(new my_data()); } int work() { for( int i = 0; i < 42; ++i ) { MY_LOG << "THIS IS A MESSAGE - I = " << i; MY_LOG << "ts_ptr = " << ts_ptr.get(); my_thread_foo(); THIS_THREAD::sleep_for( CHRONO_LIB::milliseconds(10) ); } return 0; } int main(int argc, char *argv[]) { #if LEAK_DETECTOR == BASIC_VS_LEAK_DETECTOR // First simple memory leak detection for Visual Studio // use _crtBreakAlloc to put a breakpoint on the provided memory leak id allocation //_crtBreakAlloc = 1149; _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF ); #endif //int* k = new int[42]; // to check that memory leak detection does work MY_LOG << "Hello, World!"; #ifdef TEST_ASYNC # ifndef WITH_BOOST_THREADS std::vector< std::future<int> > work_in_progress(2); # ifdef WITH_STD_ASYNC for( auto& ftr : work_in_progress ) { ftr = std::async( work ); } # else for( auto& ftr : work_in_progress ) { std::packaged_task< int() > task(work); ftr = task.get_future(); std::thread thread( std::move(task) ); thread.detach(); } # endif for( auto& ftr : work_in_progress ) { ftr.get(); } # else std::vector< boost::unique_future<int> > work_in_progress(42); for( auto& ftr : work_in_progress ) { boost::packaged_task<int> task(work); // boost's packaged_task don't take the full signature as parameter, it takes the return type only ftr = task.get_future(); boost::thread thread( boost::move(task) ); thread.detach(); } for( auto& ftr : work_in_progress ) { ftr.get(); } # endif #else for( int i = 0; i < 42; ++i ) { work(); } #endif MY_LOG << "END"; return EXIT_SUCCESS; } -------------------------------------- // this program tests if the memory leaks appear with Threading Building Blocks #define BASIC_VS_LEAK_DETECTOR 0 #define VISUAL_LEAK_DETECTOR 1 #define LEAK_DETECTOR VISUAL_LEAK_DETECTOR #define WITH_ROOT_TASK //#define WITH_BOOST_LOG //#define WITH_STD_ASYNC // uncomment to leak #ifdef WITH_STD_ASYNC # include <future> #endif #include <thread> #include <atomic> #include <boost/thread.hpp> #include <tbb/tbb.h> #include <tbb/task_scheduler_init.h> #ifdef WITH_BOOST_LOG # include <boost/log/trivial.hpp> # define MY_LOG BOOST_LOG_TRIVIAL(info) #else # include <iostream> # define MY_LOG std::cout << '\n' #endif #if LEAK_DETECTOR == BASIC_VS_LEAK_DETECTOR # define _CRTDBG_MAP_ALLOC # include <stdlib.h> # include <crtdbg.h> #else # include "vld.h" #endif namespace test { struct my_data { char data[1024]; }; boost::thread_specific_ptr< my_data > ts_ptr; void my_thread_foo() { ts_ptr.reset(new my_data()); } class UpdateTask : public tbb::task { public: UpdateTask() : idx( s_idx++ ) { MY_LOG << "[UpdateTask " << idx << " ] " << std::endl; } ~UpdateTask() { MY_LOG << "[/UpdateTask " << idx << " ]" << std::endl; } tbb::task* execute() { MY_LOG << "[" << std::this_thread::get_id() << "] Tick "<< m_count <<std::endl; my_thread_foo(); ++m_count; if( m_count < 100 ) { // make sure this is re-executed this->increment_ref_count(); this->recycle_as_safe_continuation(); } return nullptr; } private: static std::atomic<int> s_idx; std::atomic<int> m_count; const int idx; }; std::atomic<int> UpdateTask::s_idx = 0; class TaskScheduler // using TBB { public: #ifdef WITH_ROOT_TASK TaskScheduler() : m_root_task( *new (tbb::task::allocate_root()) tbb::empty_task ) { m_root_task.increment_ref_count(); } ~TaskScheduler() { m_root_task.destroy(m_root_task); } #endif void register_update_task() { #ifdef WITH_ROOT_TASK m_root_task.increment_ref_count(); UpdateTask& updater = *new(m_root_task.allocate_child()) UpdateTask(); #else UpdateTask& updater = *new(tbb::task::allocate_root()) UpdateTask(); #endif m_task_list.push_back( updater ); } void run_and_wait() { #ifdef WITH_ROOT_TASK m_root_task.spawn( m_task_list ); m_root_task.wait_for_all(); #else tbb::task::spawn_root_and_wait( m_task_list ); #endif } private: tbb::task_list m_task_list; // uncomment the following line to not leak tbb //tbb::task_scheduler_init m_engine_instance; // We explicitly create and destroy the TBB task scheduler to avoid memory leak warning noises. #ifdef WITH_ROOT_TASK tbb::task& m_root_task; #endif }; void tbb_test() { TaskScheduler task_scheduler; for( int i = 0; i < 50; ++i ) { task_scheduler.register_update_task(); } task_scheduler.run_and_wait(); } } int main(int argc, char *argv[]) { #if LEAK_DETECTOR == BASIC_VS_LEAK_DETECTOR // First simple memory leak detection for Visual Studio // use _crtBreakAlloc to put a breakpoint on the provided memory leak id allocation //_crtBreakAlloc = 148; _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF ); #endif #ifdef WITH_STD_ASYNC std::atomic<bool> finished = false; std::async( [&]{ while( !finished ) { MY_LOG << "POP"; test::my_thread_foo(); std::this_thread::sleep_for( std::chrono::milliseconds(500) ); } } ); #endif test::tbb_test(); #ifdef WITH_STD_ASYNC finished = true; #endif MY_LOG << "\nEND"; std::this_thread::sleep_for( std::chrono::seconds(4) ); return 0; }

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[thread] boost::thread and thread safety annotations
by Wladimir 04 Mar '13

04 Mar '13

Hello, The Clang C++ compiler project is currently working on a thread safety analyzer. By making use of so-called thread safety annotations within the source code, several problems with synchronization primitives can be found statically. For example: usage of a data structure without acquiring its guarding lock. See here for an overview of the available attributes: http://clang.llvm.org/docs/LanguageExtensions.html#threadsafety It is customary to use these attributes by defining macros, for compatibility: http://www.mail-archive.com/linuxkernelnewbies@googlegroups.com/msg01455.ht… At one time, it was also supposed to end up in G++, but this was abandoned in favor of clang (see http://gcc.gnu.org/wiki/ThreadSafetyAnnotation) But at least the annotations are fairly standardized. I think it would be useful to add these annotations to boost::thread, so that projects using that library can make use of the static checking. As I understand it, is only a matter of marking data structures that serve as lock/scoped_lock (such as boost::mutex, boost::recursive_mutex, ...), and methods that act upon the lock with the appropriate attributes. Any interest in this? Regards, Wladimir

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Fwd: [Thread] Solution to conflict with MFC?
by Thorsten Ottosen 28 Feb '13

28 Feb '13

Hi Thread maintainers, Anthony speaks about a patch to make this work. Does anyone know where it is? And could it be applied? Thanks -Thorsten -------- Original Meddelelse -------- Subject: [Thread] Solution to conflict with MFC? Date: Tue, 26 Apr 2011 13:28:56 +0200 From: Christian Larsen <contact(a)dword.dk> Reply-To: boost-users(a)lists.boost.org To: boost-users(a)lists.boost.org Newsgroups: gmane.comp.lib.boost.user Hello, I know this has been asked before, but I could not find a good solution. I'm experiencing problems with an application using both MFC and Boost.Thread. Specifically the assertion ASSERT(AfxGetModuleState() != AfxGetAppModuleState()); in AfxCoreInitModule() fails. I link Boost.Thread statically into a DLL in my project. From previous posts to this list and elsewhere, e.g. http://lists.boost.org/boost-users/2009/04/46929.php, I see that the issue is caused by setting _pRawDllMain in tss_pe.cpp. Commenting this line does "solve" the problem, but I would rather not have to hack the Boost source code this way. It seems there is a patch somewhere for this problem (referred to in http://lists.boost.org/boost-users/2009/04/47015.php) but it appears it never made it into the source. Is there any chance of this issue being solved in a better way? Best regards, Christian Larsen

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[Config] N3276 decltype support on VC++ 11
by Michel Morin 28 Feb '13

28 Feb '13

IIRC, Stephan said that VC++ 11 supports N3276 decltype. Shall we "undef" BOOST_NO_CXX11_DECLTYPE_N3276 for VC++ 11? This enables automatic use of decltype-based `boost::result_of`. Trivial patch attached. Regards, Michel

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[multi_index] Move Semantics
by Mark Snelling 27 Feb '13

27 Feb '13

Hi, I've been a user of Boost.MultiIndex for a number of years and think it's a great library. Is there any firm plan to add move semantics? It's been noted under "Future Work" in the docs since Boost 1.32. Regards, Mark

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[Lockfree] ringbuffer
by Rich E 17 Feb '13

17 Feb '13

First off, all Boost.Lockfree tests in trunk are passing for me on clang 4.0 on OS X, hurrah! Thank you Tim for working on this for so long... I'm running through the examples now, only with the outdated documentation as a guide (more than a couple years old). I cannot find the ringbuffer container - was it renamed or removed altogether during the review period? I notice spsc_queue acts awefully like a ringbuffer, and it's implementation contains many

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[fixed_point] Request for interest in a binary fixed point library
by Vicente J. Botet Escriba 02 Feb '13

02 Feb '13

Hi, the recent discussion on the MultiplePrecission Arithmetic library has show that some people has its ow fixed point library. Is there an interest in a Boost library having as base http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3352.html? I have started a prototype http://svn.boost.org/svn/boost/sandbox/fixed_point (there is no doc yet but the basic goal is quite close to the N3352 C++ proposal). This prototype should allow you to play a little bit with. If yes, what would you like to be changed, added or improved in n3352? Next follows some design decisions that IMO need to be decided before hand. * Should integers and reals be represented by separated classes? * Should signed and unsigned be represented by separated classes? * Should the library use a specific representation for signed numbers (separated sign, 2-complement? Let the user choose? * Should the library provide arbitrary range and resolution and allocators? * Should the library be open to overflow and rounding or just implement some of the possible policies? and in this case which ones? * Should fixed_point be convertible to/from integer/float/double? * Could the result of an arithmetic operation have more range and resolution than his arguments? * Is there a need for a specific I/O? * is there a need for radix other than 2 (binary)? * Should the library implement the basic functions, or should it imperatively implement the C++11 math functions? Could a first version just forward to the c++11 math functions? * Should the library support just one of the know ways to name a fixed-point, a U(a,b), nQm, ...? Provide some ways to move from one to another? * Could expect the same/better performances respect to hand written code? * What should be the size used by a fixed_point instance? _fast? _least? Should the user be able to decide which approach is better for his needs? * Which should be the namespace? boost? boost/fixed_point? boost/binary_fixed_point? boost/bfp? ... * others you can think of. Please, replay if you are interested, have some experience in the domain, good ideas, .. Best regards, Vicente

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