September 2009 - Boost-users

Mersenne twister problem
by ruya 19 Sep '09

19 Sep '09

Hello I've built a meta-heuristics library in which I use the boost random library. I am using several independent generators through the application. The problem is in the core of my library. The tricky part is that I have three different algorithms using the core, all of them using the class where a segmentation fault happens, but only one of them crashes when it tries to use the class, the others run as expected. Gdb points to the boost library, as you can see in the snippet bellow. I couldn't find any information on this issue, and I cannot see something wrong with my code (the relevant part is bellow). The parent class where generators are declared: template< class SType, typename MemP > class SearchFunctor{ (...) public: virtual SPtr operator()( SPtr s, int iter ) = 0; SearchFunctor(){ (...) //This is how I initialize teh generators, being MASTER SEED 666 generator1 = base_generator_type(MASTER_SEED*13); uni_dist1 = boost::uniform_real<>(0,1); uniEmp = new GeneratorI(generator1, uni_dist1); generator2 = base_generator_type(MASTER_SEED*17); uni_dist2 = boost::uniform_real<>(0,1); uniRes = new GeneratorI(generator2, uni_dist2); } protected: base_generator_type generator1, generator2; boost::uniform_real<> uni_dist1, uni_dist2; GeneratorI* uniEmp; GeneratorI* uniRes; }; The derived class using the generators: template< class SType, typename MemP > struct SwapSearch : public SearchFunctor<SType,MemP>{ typedef SearchFunctor<SType,MemP> Parent; (...) SPtr operator()( SPtr s, int iter ){ assert(s != NULL); assert(s->GetDomain()!= NULL); assert(s->GetDomain()->GetTotalEntities()>1); (...) d1 = (*Parent::uniEmp)() * (s->GetDomain()->GetTotalEntities()-1); d2 = (*Parent::uniEmp)() * (s->GetDomain()->GetTotalEntities()-1); (...) return 0; } }; The output of the debugger has a lot of lines because of meta-programming but starts and finishes with this: #0 0x08071a57 in brickheuristics::SwapSearch (...) (...) at /usr/include/boost/random/mersenne_twister.hpp:279 279 UIntType z = x[i]; Thanks -- View this message in context: http://www.nabble.com/Mersenne-twister-problem-tp25382114p25382114.html Sent from the Boost - Users mailing list archive at Nabble.com.

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[units] CODATA constant for electron charge?
by Manoj Rajagopalan 19 Sep '09

19 Sep '09

Hi developers, Could you please include the electron charge in the codata constants? Right now it has to calculated using codata::e_over_m_e*codata::m_e or set using quantity<electric_charge>::from_value() which is inconvenient. thanks, Manoj

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[Interprocess] deadlocking race condition in emulation interprocess_condition.hpp
by Young, Zachariah L 18 Sep '09

18 Sep '09

This appears related to the discussion found here: http://lists.boost.org/boost-users/2009/03/46051.php Bug: There is a set of conditions where a process can manage to enter do_timed_wait, increment m_num_waiters, and exit without decrementing it. Boost 1.39.0 Sequence of events: We join our hero, Process A (P_A), in boost/interprocess/sync/emulation/interprocess_condition.hpp. P_A is executing a do_timed_wait(true, lock, abs_time) call, and is spinning at the while loop at line 124. tout_enabled == true, and abs_time is a microsecond in the future (about to expire but hasn't yet). Process B, P_A's trusty sidekick, sends a notify_all on the conditional, breaking P_A out of the while loop at line 124. abs_time arrives (ie, P_A got to line 149 with microsec_clock::universal_time() >= abs_time and timed_out = false). With these conditions, P_A gets to line 163 and calls the constructor for scoped_lock. P_A jumps to boost/interprocess/sync/scoped_lock.hpp line 114. P_A executes mp_mutex->timed_lock(abs_time) at line 115. P_A jumps to boost/interprocess/sync/emulation/interprocess_condition.hpp line 49. P_A takes a reading of now at line 56. P_A finds that (now >= abs_time) at line 58 and is sent packing with a return value of false. P_A arrives back in boost/interprocess/sync/emulation/interprocess_condition.hpp on line 163. P_A gets to line 171 and finds lock is false. He panics! He sets timed_out to true and unlock_enter_mut to true, but in his haste to break out of evil Dr. while(1)'s clutches, he forgot to atomically decrement m_num_waiters! Manic laughter can be heard behind him as he tries in vein to acquire the lock on line 214. "You fool! You fell into my trap!", shouts Dr. while(1). "Process B grabbed that very lock and attempted to free you again! He is at line 56 of this very header file, waiting for a call from you that will never come, and he's holding your precious lock! Your deadlock is complete! HAHAHAHAHAHAH!!" Ahem. I do not know the proper way to fix this problem. My straightforward idea is to add the following line at line 172 of boost/interprocess/sync/emulation/interprocess_condition.hpp: if(!lock){ detail::atomic_dec32(const_cast<boost::uint32_t*>(&m_num_waiters)); timed_out = true; unlock_enter_mut = true; break; } However, the commment inlcuded with the block in question: //Notification occurred, we will lock the checking interprocess_mutex so that //if a notify_one notification occurs, only one thread can exit ...makes me wary. One thing seems certain to me: there's something not quite right here. I could increase my timeout window to lower the chances of this occurring, but that is not a solution. That is masking a problem. Anyone got a take on this? Am I missing something obvious? That whole block with the comment really makes me suspicious.

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Using Boost Mutex
by Wesley Bland 18 Sep '09

18 Sep '09

This is firmly in n00b territory. I'm trying to use a boost::mutex to lock a STL queue. The mutex is stored in a class in a map. When I pass the mutex to the boost::mutex::scoped_lock constructor, I get this error: /usr/local/include/boost/noncopyable.hpp: In copy constructor ‘boost::mutex::mutex(const boost::mutex&)’: /usr/local/include/boost/thread/pthread/mutex.hpp:31: instantiated from ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = int, _Tp = boost::mutex, _Compare = std::less<int>, _Alloc = std::allocator<std::pair<const int, boost::mutex> >]’ SwitchBox.cpp:15: instantiated from here /usr/local/include/boost/noncopyable.hpp:27: error: ‘boost::noncopyable_::noncopyable::noncopyable(const boost::noncopyable_::noncopyable&)’ is private /usr/local/include/boost/thread/pthread/mutex.hpp:31: error: within this context /usr/include/c++/4.2.1/bits/stl_map.h: In member function ‘_Tp& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = int, _Tp = boost::mutex, _Compare = std::less<int>, _Alloc = std::allocator<std::pair<const int, boost::mutex> >]’: /usr/include/c++/4.2.1/bits/stl_map.h:350: note: synthesized method ‘boost::mutex::mutex(const boost::mutex&)’ first required here This appears to be complaining about me passing the mutex into the scoped_lock. Can anyone give me some help here? I've included a much shortened version of the code that otherwise compiles. Thanks for your help, Wesley SwitchBox.hpp ----- #include <map> #include <queue> #include <boost/thread/mutex.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; using namespace std; namespace Network { typedef struct Message { int type; unsigned long sender; unsigned long destination; int size; void *body; char *PackHeader(); void UnpackHeader(char *); } Message; class SwitchBox { protected: unsigned long myID; int headerSize; map< int, queue< Message > > sendQueues; map< int, boost::mutex > sendMutexes; bool Initialize(); void SendThread(unsigned long id, tcp::socket sock); }; } SwitchBox.cpp ------ #include "Switchbox.hpp" using namespace Network; bool SwitchBox::Initialize() { myID = 0; headerSize = sizeof(int) + sizeof(unsigned long) * 2 + sizeof(int); return true; } void SwitchBox::SendThread(unsigned long id, tcp::socket sock) { // Set up the lock so it can be locked and unlocked as we need boost::mutex::scoped_lock sendLock(sendMutexes[id], boost::defer_lock); while (true) { // First get the message off of the message queue // Lock the message queue so nothing is moved unexpectedly sendLock.lock(); Message m = sendQueues[id].front(); sendQueues[id].pop(); // Unlock the message queue so everyone else can get to it now sendLock.unlock(); // Next send the message through the socket boost::asio::write(sock, boost::asio::buffer(m.PackHeader(), headerSize)); boost::asio::write(sock, boost::asio::buffer((char *) m.body, m.size)); } }

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Can the Regex code be placed into a class?
by Ramon F Herrera 18 Sep '09

18 Sep '09

The following sample program comes with the Boost Regex distribution. It compiles and runs fine. Its purpose is to count the number of classes in the input text file. http://patriot.net/~ramon/regex_iterator_example.cpp.txt I am having a real hard time trying to convert the code to a class (named "Pairs"). The compilation problem occurs in this statement: std::for_each(m1, m2, &regex_callback); The compiler suggests to use this statement, which does not compile either: std::for_each(m1, m2, &Pairs::regex_callback); Thanks, -Ramon http://www.parashift.com/c++-faq-lite/pointers-to-members.html

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boost::function typename Signature
by veerus 18 Sep '09

18 Sep '09

How to extract the return type and the argument type list from the type Signature in boost::function<Signature> ? More specifically if I have a object of type boost::function< int ( double) >, the thing "int (double)" is matched with a type. What type is that ? Where can I find it? Thanks -- View this message in context: http://www.nabble.com/boost%3A%3Afunction-typename-Signature-tp25507953p255… Sent from the Boost - Users mailing list archive at Nabble.com.

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[Regex] Which sub-expression did participate in a partial match?
by Kay-Michael Wuerzner 18 Sep '09

18 Sep '09

Hello, I wonder if it is possible to find out which sub-expression of a regex is responsible for a partial match? Consider the following example: int main ( int argc, char** argv ) { std::string input ( argv[1] ); boost::regex test ( "((?:Apple )?iPhone)|(Sony Vaio)" ); boost::sregex_iterator it ( input.begin(), input.end (), test, boost::match_default | boost::match_partial ); boost::sregex_iterator none; if ( it != none ) { std::cout << (*it).size () << std::endl; if ( (*it)[0].matched ) std::cout << "full match\n"; else std::cout << "partial match\n"; for ( unsigned int i = 1; i < (*it).size (); ++i ) { if ( (*it)[i].matched ) // this should in principle also be true for partial matches std::cout << i << " " << (*it).position () << std::endl; } } return 0; } The problem is that the if-condition in the for loop is not met in case of a partial match on the sub-expression: $> ./regex_test "Apple" partial match $> ./regex_test "iPhone" full match 1 0 In the first case I would expect the output of the sub-expression and the position of the match. Are you aware of any method to achieve this behavior? Many thanks in advance, Kay

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shared_ptr and pass by value
by Marat Abrarov 18 Sep '09

18 Sep '09

Dear Boost C++ Libraries Developers, According to http://cpp-next.com/archive/2009/08/want-speed-pass-by-value/ why Boost use this (not the only example): ~~~~~~~~~~~~~~~~~~~ shared_ptr & operator=( shared_ptr const & r ) { this_type(r).swap(*this); return *this; } ~~~~~~~~~~~~~~~~~~~ and not such: ~~~~~~~~~~~~~~~~~~~ shared_ptr & operator=( shared_ptr r ) { r.swap(*this); return *this; } ~~~~~~~~~~~~~~~~~~~ Regards, Marat.

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[format] compilation error
by Johan Råde 18 Sep '09

18 Sep '09

Hi, I'm using Boost 1.38 and Visual Studio 2008. The following code #include <boost/format.hpp> #include <ostream> #include <vector> using boost::format; using std::ostream; using std::vector; ostream& operator<<(ostream& os, const vector<int>& v) { os << '['; for(size_t i = 0; i < v.size(); ++i) { if(i > 0) os << ' '; os << v[i]; } os << ']'; return os; } void f() { vector<int> v; str(format("%1%") % v); } fails to compile with the error message 1>c:\libraries\boost\boost_1_38_0\boost\format\feed_args.hpp(100) : error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const std::vector<_Ty>' (or there is no acceptable conversion) 1> with 1> [ 1> _Ty=int 1> ] Why? How do I fix this? Thank you, Johan Råde

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[Math] Bug in example code / doc (Binomial Distr.)
by Ralf M. 18 Sep '09

18 Sep '09

On p.66 (Binomial distribution, "Binomial Quiz Example") of the Math Toolkit pdf-file, and also at http://www.boost.org/doc/libs/1_40_0/libs/math/doc/sf_and_dist/html/math_to… it is written: "Probability of getting exactly 11 answers right by chance is 2.32831e-010" I think this is wrong. It rather should be one of these below: "Probability of getting exactly 11 answers right by chance is 0.000247132" or "Probability of getting exactly 16 answers right by chance is 2.32831e-010" I have'n checked the underlying source code of this yet; ie. maybe it is only a doc error... And this code there seems IMHO to be problematic too: " int questions = 16; // All the questions in the quiz. int answers = 4; // Possible answers to each question. double success_fraction = (double)answers / (double)questions; // If a random guess. // Caution: = answers / questions would be zero (because they are integers)! binomial quiz(questions, success_fraction); " Shouldn't the second param not simply be the constant p of each item, ie. here 0.25, even if # of questions is set to a different value, for example 32 ? Because 32 / 4, as done above, wouldn't be 0.25 anymore...

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