May 2008 - Boost - lists.preview.boost.org

[future] Early draft of wait for multiple futures interface
by Johan Torp 07 Jun '08

07 Jun '08

We've been discussing the need to implement a mechanism to wait for multiple futures in a separate thread: www.nabble.com/Review-Request%3A-future-library-%28Gaskill-version%29-to166… I've come up with some interfaces which I find intuitive and useful. I've never implemented thread waiting, so please let me know if you think something like this is viable. ------------------------------ Proposal ------------------------------ A future can be constructed and thereafter wait on four different "future conditions" * a promise * a future_switch * a future_barrier * another future Each condition has a specified return type and the futures you create from it must match this type. They all have the same possible states - isn't ready, has value or an expression. I have left these and alot of other details out of the interface below for conciseness. ------------------------------ Interface drafts ------------------------------ /// Future condition which is ready when any of the added conditions is ready. Has an arbitrary return-type template<class ReturnType> class future_switch { public: /// Direct return template<class FutureConditionWithMatchingReturnType> void add_case(FutureConditionWithMatchingReturnType f); /// Possibility to perform custom functor, bind state, perform some logic etc before fulfilling it's condition template<class FutureCondition, class FutureTypeToReturnTypeFunctor> void add_case(FutureCondition f, FutureTypeToReturnTypeFunctor case); /// Only valid in is_ready state. Removes last fulfilled futurecondition and enables new futures to be /// constructed. Existing futures will have copied the value or exception already and will still work. void remove_ready_case(); bool empty() const; }; /// Future condition which is ready when all added futures are. /// This interface is less promising and has some flaws. Maybe you can get inspired by it though. template<class ReturnType> class future_barrier { public: future_barrier(const function<ReturnType()>& onReady); template<class FutureCondition> void add_condition(const future<FutureType>& f); }; ------------------------------ Example usage ------------------------------ template<class T> future_switch<T> operator||(const future<T>& lhs, const future<T>& rhs) { future_switch<T> sw; sw.add_case(lhs); sw.add_case(rhs); return sw; } template<class T> T and_impl(const future<T>& lhs, const future<T>& rhs) { return lhs.get() && rhs.get(); } template<class T> future_barrier<T> operator&&(const future<T>& lhs, const future<T>& rhs) { // Rather large runtime insecurity, we might forget to add lhs and rhs as conditions to the barrier future_barrier b(bind(&and_impl, lhs, rhs)); b.add_condition(lhs); b.add_condition(rhs); return b; } // This is an experimental use case for using switch as a dynamic set of future conditions // It handles three future responses and calls the three functions on the next lines bool handle_response_a(ResponseA r); bool handle_response_b(ResponseB r); bool handle_response_c(ResponseC r); void handle_pending_requests(const future<ResponseA>& a, const future<ResponseB >& b, const future<ResponseC >& c) { future_switch<void> sw; sw.add_case(a, &handle_repsonse_a); sw.add_case(b, &handle_repsonse_b); sw.add_case(c, &handle_repsonse_c); bool all_ok = true; while (!sw.empty()) { // Will automatically remove ok:ed futures from sw future<bool> next_response_was_ok(sw); bool all_ok = all_ok && next_response_was_ok.get(); sw.remove_ready_case(); } return all_ok; } ------------------------------ Some comments ------------------------------ There is a lot to improve here. I'd appreciate it if we could focus on determining whether this is a viable solution and the way we want to go before diving into details. These abstractions has the following property: A Users can compose conditions and poll them without the need of waiting. B We do not need to spawn extra threads for waiting - we only wait on the "outmost" future C Threads needn't awake and poll readiness - assuming the and/or logic is handled by waitingcode. D No "user logic" from the future-blocking threads propagate to the promise-fulfilling thread. E It's possible to implement efficient laziness by keeping readiness/waiting logic internal in the future library "wait for all" can be implemented without adding future_barrier, by simply calling wait() on all futures. We lose property A and E for "wait for all" if we do it this way. The blocking thread will awake unnecessarily many times. Property C means promise-fullfilling threads need to do some basic and/or logic. I think this can be implemented in a safe and efficient manner, O(log(N)) for barrier/all and O(1) for switch/any. I also think it is much preferable to waking and switching to future-blocking threads which re-check readiness conditions. Note property D. Whatever mechanism we choose I think it's desirable to be able to easily "lift" existing functions to futures; R foo(A1 a1, A2 a2, A3 a3) should be easily rewritable as; future<R> foo(future<A1> a1, A2 a2, future<A3> a3) // Some parameters need not be lifted Johan -- View this message in context: http://www.nabble.com/-future--Early-draft-of-wait-for-multiple-futures-int… Sent from the Boost - Dev mailing list archive at Nabble.com.

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Updated version of futures library
by Anthony Williams 06 Jun '08

06 Jun '08

Hi all, I've updated my futures library to include wait_for_any() and wait_for_all(). The provided overloads allow either waiting on up to five futures known at compile time: unique_future<int> f1; shared_future<std::string> f2; unique_future<double> f3; unsigned const ready_index=wait_for_any(future1,future2,future3); or on a container of futures: std::vector<jss::shared_future<int> > futures; std::vector<jss::shared_future<int> >::iterator const future= jss::wait_for_any(futures.begin(),futures.end()); In the first instance, they can be of distinct types, but in the latter, all the futures in the container must be of the same type. The documentation is available at http://www.justsoftwaresolutions.co.uk/files/futures_documentation.html and the files and tests are available at http://www.justsoftwaresolutions.co.uk/files/n2561_futures_revised_20080530… Anthony -- Anthony Williams | Just Software Solutions Ltd Custom Software Development | http://www.justsoftwaresolutions.co.uk Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL

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[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?

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Rounding, Truncating Values
by Tom Brinkman 05 Jun '08

05 Jun '08

Here are a few small utility functions that I use for rounding and truncating values. Its probably a good idea to add this functionality to boost. However, I'm sure that the implentations could be significantly improved. enum RoundDirection { rd_AwayZero=0, rd_TowardZero=1, }; template <class A> inline A roundTo(A val, int decimalPlaces) { double mult=pow(10.0, decimalPlaces); return round(val*mult)/mult; } template <class A> inline A roundTo(A val, int decimalPlaces, RoundDirection rd) { A ret; double mult=pow(10.0, decimalPlaces); bool less0=(val<0.0 ? true : false); if (less0) { if (rd==rd_AwayZero) rd=rd_TowardZero; else if (rd==rd_TowardZero) rd=rd_AwayZero; } switch (rd) { case rd_AwayZero: ret=ceil(val*mult)/mult; break; case rd_TowardZero: ret=floor(val*mult)/mult; } return ret; } template <class A> inline A truncTo(A val, int decimalPlaces) { double mult=pow(10.0, decimalPlaces); return trunc(val*mult)/mult; }

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BOOST documentation in PDF/PS format
by dhruva 03 Jun '08

03 Jun '08

Hello, I am looking for the BOOST library in either PDF/PS formats so that I can print the ones I need and read them offline (which I generally prefer). Reading though the boost documenting link, it appears quite a daunting task to setup boost doc build to generate PDF files (it has a bunch of dependencies). Is there any location from where I can download the PDF files for the current release version of BOOST or any plans for providing the same in the near future? with best regards, dhruva -- Contents reflect my personal views only!

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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

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[Graph] compile error while inheriting boost graph
by Sandeep Gupta 01 Jun '08

01 Jun '08

Hi, My attempt to inherit boost graph failed. The compiler complains that it is not aware of boost graph classes. Would appreciate if someone can tell if this due to boost intricacies or just regular mistake in the syntax. //Declare boost graph within namespace boostd namespace boostd { typedef adjacency_list<listS, listS, ... > Graph; typedef graph_traits<Graph>::vertex_descriptor Vertex; } class DerivedGraph: public boostd::Graph{ public: class Node: public boostd::Vertex{ //error on this line }; }; The compiler complains error: expected class-name before '{' token Thanks sandeep

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Non pre-emptible Boost.Thread
by Edd Dawson 31 May '08

31 May '08

Hello, A while ago, I implemented the Boost.Thread API in terms of Windows Fibers and <uncontext.h> functionality. The result is the ability to run code written with boost threads in a single OS thread. I find it useful for writing tests where determinism is important i.e. to test algorithmic correctness in isolation from synchronization- related concerns. I haven't updated it to mirror the new 1.35 API yet, but I was wondering if any other boost users would be interested in this or if it might be thought suitable for inclusion in the boost library collection. More information is available here: http://www.mr-edd.co.uk/?page_id=91 Direct link to source code: http://www.mr-edd.co.uk/files/coco/coco-0.2.0.zip Kind regards, Edd

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[thread] warnings when linking with the dynamic thread library on cygwin
by vicente.botet 31 May '08

31 May '08

Hello, I have a warning when linking with the thread library. /usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: warning: auto-importing has been activated without --enable-auto-import specified on the command line. When I set <library>/boost/thread//boost_thread/<link>static; instead of <library>/boost/thread//boost_thread; this works without warnings. What I need to do to link dynamically without warnings? Best regards Vicente ================== Command $ bjam The jamfile contains using testing ; if ! $(BOOST_ROOT) { BOOST_ROOT = [ modules.peek : BOOST_ROOT ] ; } project : : requirements <include>$(BOOST_ROOT) <include>../../.. <threading>multi <target-os>cygwin <threadapi>pthread <variant>debug <library>/boost/test//boost_unit_test_framework/<link>static <threading>multi <library>/boost/thread//boost_thread; Link warning: gcc.compile.c++ ..\..\..\bin.v2\libs\sync\test\include_concurrent_component.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\include_concurrent_component.o **passed** ..\..\..\bin.v2\libs\sync\test\include_concurrent_component.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\include_concurrent_component.test gcc.compile.c++ ..\..\..\bin.v2\libs\sync\test\static_thread_group_test.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\static_thread_group_test.o gcc.link ..\..\..\bin.v2\libs\sync\test\static_thread_group_test.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\static_thread_group_test.exe /usr/lib/gcc/i686-pc-cygwin/3.4.4/../../../../i686-pc-cygwin/bin/ld: warning: auto-importing has been activated without --enable-auto-import specified on the command line. This should work unless it involves constant data structures referencing symbols from auto-imported DLLs.Info: resolving vtable for boost::detail::thread_data_baseby linking to __imp___ZTVN5boost6detail16thread_data_baseE (auto-import) testing.capture-output ..\..\..\bin.v2\libs\sync\test\static_thread_group_test.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\static_thread_group_test.run 1 fichier(s) copi?(s). **passed** ..\..\..\bin.v2\libs\sync\test\static_thread_group_test.test\gcc-3.4.4\debug\target-os-cygwin\threadapi-pthread\threading-multi\static_thread_group_test.test ...updated 6 targets... --------------------------- Vicente Juan Botet Escriba

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[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

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