March 2009 - Boost - lists.boost.org

[mirror] -- RFC
by Matus Chochlik 31 Mar '09

31 Mar '09

Dear Boosters, The Mirror library has been around for nearly a year. I would like to start doing the preparations for getting the library ready for a formal review and before that I would like to hear your opinions on whether this library actually belongs to Boost and any suggestions on how to improve it or what to change. For those of you who are not familiar with it, Mirror is a compile-time reflection facility with some run-time features. The sources can be downloaded from the Vault or checked out from the Sandbox (http://svn.boost.org/svn/boost/sandbox/mirror/) Since the docs (http://tinyurl.com/atba2k) do not cover everything yet, you can see the usage of several of the implemented but undocumented features in the test suite and in the examples (http://tinyurl.com/c4xygh) Some people have found the Concept browser (http://tinyurl.com/czz3t2) to be a good starting point and a useful quick reference. It, however, requires a XSLT capable web browser. It is known to work with MSIE 7+ and Firefox 3.x.y without the need to install any other software. Best regards, ________________ ::matus_chochlik

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[thread] Error: cannot open file 'libboost_thread-vc90-mt-gd-1_38.lib'
by Santosh Naidu 31 Mar '09

31 Mar '09

Hi All, I am new to Boost. I am getting the following error when I try to include <boost/thread/condition_variable.hpp> Error 1 fatal error LNK1104: cannot open file 'libboost_thread-vc90-mt-gd-1_38.lib' I have followed all the steps to setup the boost library given in the startup document. Regards, Santosh

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[thread] Assertion failed get_system_time_sentinel()
by Filip Klasson 31 Mar '09

31 Mar '09

Hi, I get Assertion failed timed_lock(::boost::detail::get_system_time_sentinel()), file c:\boost\thread\win32\basic_timed_mutex.hpp, line 64. Code in basic_timed_mutex.hpp: void lock() { BOOST_VERIFY(timed_lock(::boost::detail::get_system_time_sentinel())); //Line 64 } Code in thread_time.hpp: namespace boost { ... namespace detail { inline system_time get_system_time_sentinel() { return system_time(boost::posix_time::pos_infin); } ... } } I read in a previous thread that this was a known bug that is fixed in Boost 1.38 but i am using Boost 1.38. Is this another bug or is it not fixed? This only happends sometimes and it happends when i call wait on a condition variable. Here is my code, i have marked where Assertion failed happends. boost::mutex::scoped_lock lock(_mutex); while(_queue.empty()) { _condition.wait(lock); } //Assertion failed happends here. //Another thread is signaling the condition variable when an element is added to the _queue. I am happy with all sorts of helpful comments. Best regards

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[iostreams] binary memory stream
by Kenny Riddile 31 Mar '09

31 Mar '09

I'm still pretty inexperienced with the iostreams library, so this may be a simple question. I'm trying to use GIL to write a PNG to a memory stream instead of a file stream. The write_view() function in the new version of GIL's io extension expects an ostream opened in binary mode as it's first parameter, such as: using namespace std; using namespace boost::gil; ofstream outputStream( "foo.png", ios::out | ios::binary ); write_view( outputStream, const_view(image), png_tag() ); I'm attempting to write to memory instead of a file, by doing this: using namespace boost::gil; using namespace boost::iostreams; typedef stream< back_insert_device< std::vector<char> > > BufferStream; std::vector<char> buffer; BufferStream bufferStream( buffer ); write_view( bufferStream, const_view(image), png_tag() ); The data that ends up in buffer is identical to the data that ends up in foo.png from the first example if I don't open outputStream in binary mode. So how can I make a binary memory stream with the iostreams library? Do I need to write my own filter?

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Re: [boost] unicode tools and an unicode string type
by Graham 31 Mar '09

31 Mar '09

8. Re: [gsoc] unicode tools and an unicode string type (Mathias Gaunard) >It's really aimed at being simple and non-intrusive. Components are >fairly separate and code is thus incremental, and the unicode string >just composes the work. > >I personally believe basic_string, char_traits, and codecvt facets and >the standard locale system are not really suitable to deal with unicode, >which may have been the reason why previous proposals ended up they way >they did. >I think some people said the same in the various unicode discussions, too. >Efficient algorithms are provided by the Unicode consortium, so it's >mostly just the design or glue code that needs work. >The glue depending on what integration with other components is being >done. Here, it's mostly just range concepts. Mathias, Unfortunately the simple algorithms supplied by the Unicode consortium all end up requiring a character traits tables ! There are large tables that need to be transformed into compact sets of traits and this was done by myself and Rogier. These traits are then used to drive simple [ish] rules. So whatever you do - you need to start with the character traits tables [which are large]. Yours, Graham Barnett

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Re: [boost] unicode tools and an unicode string type
by Graham 31 Mar '09

31 Mar '09

> Re: [gsoc] unicode tools and an unicode string type (Mathias Gaunard) Mathias, We are overdue a full string Unicode support library in boost. Rogier and I developed the Unicode character library that was going to underly the Unicode string libraries to provide full Unicode char, string, and iterator support [grapheme, word, paragraph iterators etc] but never had time to complete it. Any compliant Unicode text presentation system will need this and it is not possible to write a compliant Unicode text editor without it. Please have a look at the Unicode character library at: http://www.boostpro.com/vault/ Unicode_lib.zip. Good luck. Yours, Graham Barnett

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[proto] transforms && rvalue refs
by troy d. straszheim 30 Mar '09

30 Mar '09

I'm playing with proto on gcc 4.3 with c++0x enabled and trying to see if I can use rvalue refs inside callable transforms, to tell what is/isn't temporary while transforming an expression. I have a different way to do this, involving embedding the 'rvalueness' of an object in its type... yuck. Hopefully something better is out there. The use case: a = exp(exp(b)); (as below), where a and b are terminals and exp is a proto lazy function. This expression should result in only one copy of b... You'd want the inner call 'exp(b)' to see that it is being passed an lvalue, copy the value to a temp, modify and return std::move(temp). The outer call to exp() should see that an rvalue has arrived and feel free to overwrite it and return it by std::move. I think. The closest I can get is below. I thought I'd ask for a sanity-check on this before go any further... I have the feeling the check will come back negative. Thanks in advance, -t #include <boost/proto/proto.hpp> #include <boost/ref.hpp> #include <cassert> namespace bp = boost::proto; // // Tag for calls to exp() in our DSEL // struct exp_tag { friend std::ostream& operator<<(std::ostream& os, exp_tag) { return os << "exp_tag"; } }; // // The terminal. Assume this thing is very heavy. Some construtors // have assert(0) in them to verify they aren't called. // // struct array_impl { std::string name; array_impl() : name("NONAME") { } array_impl(const std::string& name_) : name(name_) { std::cout << "name=" << name << "\n"; } // // constructors // array_impl(array_impl& rhs) : name(rhs.name + "_copied") { } array_impl(const array_impl& rhs) : name(rhs.name+ "_copied") { } array_impl(array_impl&& rhs) { name.swap(rhs.name); name += "_moved"; } array_impl& operator=(array_impl&& rhs) { name.swap(rhs.name); name += "_moved"; return *this; } // // not called // array_impl& operator=(array_impl& rhs) { assert(0); // just to be sure what is and isn't getting called } array_impl& operator=(const array_impl& rhs) { assert(0); // just to be sure what is and isn't getting called } array_impl& operator=(const array_impl&& rhs) { assert(0); // just to be sure what is and isn't getting called } friend std::ostream& operator<<(std::ostream& os, const array_impl&) { return os << "array_impl"; } }; // // The transform for calls to exp. You'd like to be able to see if // this is getting called with a movable object. // struct UnaryFnCall : bp::callable { typedef array_impl result_type; template <typename Tag> result_type operator()(Tag, const array_impl& t) { std::cout << "transform a const ref\n"; array_impl tmp(t); return std::move(tmp); } template <typename Tag> result_type operator()(Tag, array_impl&& t) { // this guy doesn't get called, but I'd like him to. assert(0); // if this trips, something good happened. return std::move(t); } }; struct Grammar : bp::or_<bp::when<bp::terminal<array_impl>, bp::_value>, bp::when<bp::unary_expr<exp_tag, Grammar>, UnaryFnCall(exp_tag(), Grammar(bp::_child0))> > { }; template <typename T> struct Expression; struct Domain : bp::domain<bp::pod_generator<Expression>, Grammar> { }; template <typename Expr> struct Expression { BOOST_PROTO_EXTENDS(Expr, Expression<Expr>, Domain); }; template<class T> typename bp::result_of::make_expr< exp_tag, Domain, T& >::type exp (T&& t) { return bp::make_expr<exp_tag, Domain>(boost::ref(t)); } // // Our expression type that // struct array : public Expression<bp::terminal<array_impl>::type> { typedef array_impl impl_t; impl_t& self() { return boost::proto::value(*this); } array() { assert(0); } array(const std::string& name) { self().name = name; } array(const array&) { assert(0); } array(array&&) { assert(0); } template <typename Expr> array& operator=(Expr const& expr) { bp::display_expr(expr, std::cout); BOOST_MPL_ASSERT(( bp::matches<Expr, Grammar> )); typedef typename boost::result_of<Grammar(Expr const&)>::type result_t; result_t r = Grammar()(expr); self().operator=(std::move(r)); return *this; } }; int main(int, char**) { array a("a"), b("b"); // Here, only one copy is made a = exp(b); std::cout << "a's name:" << a.self().name << "\n\n"; // Here, two copies are made a = exp(exp(exp(b))); std::cout << "a's name:" << a.self().name << "\n"; }

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[gsoc] unicode tools and an unicode string type
by Mathias Gaunard 30 Mar '09

30 Mar '09

I plan to submit during the week my proposal for the Summer of Code about Unicode. I plan to provide: - iterator adaptors to iterate sequences of code units, code points and graphemes, and eventually more, from a sequence in UTF-8, UTF-16, UCS-2 or UTF-32/UCS-4. - miscellaneous utilities, such as categorization of code points - normalization functions - comparisons but not collations - substring search algorithms - and finally, an unicode string type I am well aware defining yet another new string type is quite controversial, but I believe this is quite useful. A dedicated type would be able to maintain certain invariants, such as maintaining a special normalization form. Also, I believe it can be possible to come up with a string design that allows easy integration with any other existing string type, such as the ones from the standard or Qt.

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[Boost] How to generate a Bernuolli number under probablity p
by Barco You 30 Mar '09

30 Mar '09

Hi, I want to randomly generate a Bernuolli number [0, 1],with probability p ~[0 1]. How to do that with boost? Thanks! -- ------------------------------- Enjoy life! Barco You

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"[gsoc] Thread scheduler support for boost"
by Indradip Ghosh 30 Mar '09

30 Mar '09

Hi Phil and Hartmut, I am following up with the earlier thread on of extending the current threadpool library present in boost. The current approach implements N:M model by internally using the pthread APIs (pthread_schedule() and its related classes). However, for high performance latency sensitive application code, we would not only like to parellize but would also like to (i) reduce load variance against the threads (ii) create asymmetric scheduling: where a set of threads are forced to run on a subset of processors (iii) prioritize the tasks amongst threads.. One that I am thinking is to create a userland scheduler through which all scheduling decisions are made. For OS specific case, the userland scheduler can be made to use features exposed by the OS such as different scheduling algos, processor affinity,... Please let me know if you think that this direction is admissible as a plausible extension for the Boost library. I am working on this and would be sending you more details on how i think on implementing this. Regards, Indradip. > Message: 4 > Date: Wed, 25 Mar 2009 07:36:12 -0500 > From: "Hartmut Kaiser" <hartmut.kaiser(a)gmail.com> > Subject: Re: [boost] "[gsoc] Thread scheduler support for boost" > To: <boost(a)lists.boost.org> > Message-ID: <49ca2540.47c1f10a.61b0.ffffdbac(a)mx.google.com> > Content-Type: text/plain; charset="us-ascii" > >> However, I thought of your suggested extension of threadpool class >> exploiting processor affinity techniques and it sounds very >> interesting as well but I guess we would run into the same portability >> issues with regard to availability of the lower level API exposing the >> hooks to be able to develop such a facility. Another issue would be to >> qualify and justify how much improvement would this type of >> parallelism enable on top of the instruction level parallelism already >> in place for all modern processors. Although, I would still like to >> find out if you have any concrete lead in mind. > > FWIW, processor affinity is supported on many operating systems, so it > shouldn't be problematic to come up with a portable implementation. > Moreover, I believe Oliver already included something like that into his > thread_pool library (see http://tinyurl.com/cqgt5u, file > boost-threadpool.v24.tar.gz). > >> I know for sure that there are those hard engineering problems in high >> performance computing domain to ensure QOS guarantees to distributed >> real-time embedded systems. They look into processor utilization >> optimizations in the face of uncertainty of computational load on the >> system. These usually require some kind of mathematical validation of >> the scheme for the system under construction. I guess that would be >> beyond the scope of the GSOC project, given the time frame. > > I'm sure that controlling processor affinity is something to consider not > only for real time applications or high end computing. With the rising > number of cores in a chip we need to be able to influence this for everyday > tasks as well. But that's only IHMO. > >> M:N type of models would also have the same portability issue as it >> requires changing kernel code as well as the userland code in thread >> library. > > You shouldn't shy away of some feature just because Boost requires portable > implementations. Most of the time this is possible to achieve, as modern > OS's have very similar functionality, just exposed using different API's. > > Regards Hartmut >

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