December 2008 - Boost-users - lists.preview.boost.org

Meaning of or_<> with empty arguments
by Reetesh Mukul 15 Dec '08

15 Dec '08

Hi, This code compiles:- #include <boost/mpl/or.hpp> using boost::mpl; int main() { typedef boost::mpl::or_<> A; A a; } What is the meaning an empty or_<> ? On my gcc compiler I can see that there is no type/value inside A. With Regards, Reetesh Mukul

2 3

[Regex] problems compiling with gcc 4.4
by Aonghus Lawlor 14 Dec '08

14 Dec '08

Hi, I am using boost 1.37 on osx from macports and I have a problem using the regex library with gcc 4.4, although it seems to work perfectly with gcc 4.3 and 4.2. The problem is with creating a boost::regex object- simple program below: #include <boost/regex.hpp> #include <string> int main(int argc, char **argv) { std::string s("(.*)bar|(.*)bah"); boost::regex re_node(s); return 1; } The backtrace it produces is below: (gdb) bt #0 0x90d90b9e in __kill () #1 0x90d90b91 in kill$UNIX2003 () #2 0x90e07ec2 in raise () #3 0x90e1747f in abort () #4 0x0026792c in __gnu_cxx::__verbose_terminate_handler () #5 0x00265239 in __cxxabiv1::__terminate () #6 0x0026527d in std::terminate () #7 0x0026539c in __cxa_throw () #8 0x001eeb00 in std::__throw_bad_cast () #9 0x00370d25 in std::use_facet<std::messages<char> > () #10 0x00127c93 in boost::re_detail::cpp_regex_traits_base<char>::imbue () at cpp_regex_traits.hpp:215 #11 regex_data [inlined] () at basic_regex.hpp:173 #12 basic_regex_implementation (this=0x500200) at cpp_regex_traits.hpp:93 #13 0x001256a6 in shared_ptr<boost::re_detail::basic_regex_implementation<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > > > [inlined] () at shared_ptr.hpp:525 #14 boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign (this=0xbfffe790, p1=0x5001ec "(.*)bar|(.*)bah", p2=0x5001fb "", f=0) at basic_regex.hpp:525 #15 0x00001d6a in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::assign () #16 0x00001d3e in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::assign<std::char_traits<char>, std::allocator<char> > () #17 0x00001c9f in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::basic_regex<std::char_traits<char>, std::allocator<char> > () #18 0x00001b20 in main () (gdb) Is this a problem with boost, or with the compiler? Any ideas for a fix? many thanks, a

3 5

Re: [Boost-users] [boost] [review][constrained_value] compile-time lambdas
by Gordon Woodhull 14 Dec '08

14 Dec '08

>> I guess we have to wait for decltype to be able to use lambda >> expressions as predicates here? > > Why? There are already examples with lambda predicates in the docs. Yes, constrained_value does support lambdas at runtime using runtime boost::function. I was hoping that we will also be possible to specify lambdas at compile time, which is more efficient because boost::function incurs cost equivalent to a virtual method call (it prohibits inlining and dereferences a pointer). And there is the cost of storing the function pointer too... I am imagining things like constrained_value<int, decltype(_1>0 && ! bind(isnan,_1))>. In my perfect imaginary world this would be a zero-size predicate which is default constructable because it carries no data. Thus the expression doesn't need to be duplicated on construction and is stored entirely in the constrained_value typedef. 0 might have to be construct<mpl::integral_c<0> >() :-D I'm sure there are 1000 things wrong with this, just fantasizing... I guess this also falls into the bin of "what's the perfect predicate library?"

3 2

Confused with Lambda library usage
by QPlace 14 Dec '08

14 Dec '08

Cannot figure out how to properly use lambda library in following situation (pseudo-code below): class Unit { }; class Test { public: void dosmth(Unit* unit) {} }; int main() { vector<Unit*> lst; Test t; for_each (lst.begin(), lst.end(), ?// I want to call t.dosmth with each Unit* in list } Any help will be greatly appreciated.

3 5

Sobol generator
by Laurent GIORELLO 13 Dec '08

13 Dec '08

Hi all, In GSL, we can find an implementation for the sobol distribution (quasi monte carlo). Maybe we could insert this into Boost. Cheers, Laurent

1 0

Normal distribution
by Laurent GIORELLO 13 Dec '08

13 Dec '08

Hi all, I've read the implementation for the normal distribution and I've seen people wanted Box-Muller algorithm. Instead, I suggest Marsaglia method. Instead of using cos and sin, we use a square soot. The advantage is that we already use the square root for the log. Then it's really faster. Anybody for this ? Laurent

1 0

Abstract factory
by Jason Felice 13 Dec '08

13 Dec '08

Does boost have an abstract factory? I'm reading through Alexandrescu's "Modern C++ Design" and finding the idea neat, and I'm surprised to not find an equivalent in boost. Or alternately, is there another preferred solution?

3 3

thread_group / removal of items
by Christian Ost 13 Dec '08

13 Dec '08

Hi, I have a question concerning the removal from entries of a thread_group. Consider the following code (i am working on a small threaded server): in TCPServer.h: boost::thread_group threads in TCPServer.cpp: int TCPServer::loop(int listen_fd) { for (;;) { [connect client] boost::thread* thrd = new boost::thread(boost::bind(&TCPServer::readMessages, this, rfd)); threads.add_thread(thrd); } } } int TCPServer::readMessages(int rfd) { boost::this_thread::at_thread_exit(boost::bind(&TCPServer::exitThread, this)); for(;;) { [read message] if ([buffer is empty]) { [close connection] return(0); } } return 1; } void TCPServer::exitThread() { cout << "thread exited" << endl; } Now I would like to remove the exited thread from the thread_group, however to do this I would need its thread* object - but the maximum of information I can get from boost::this_thread is a boost::thread::id and I haven't found a possibility to get a thread by its thread::id so far. How can/should I solve this issue? I would be quite happy about any advice... Thank you very much! Christian

3 2

seeking comments on 'weak_key_map' experiments
by Nicolas Lelong 13 Dec '08

13 Dec '08

Hello, I've been doing too much Python recently - thanks to boost.python - and my return in the c++ world in quite painful. To help me manage some of my objects lifetime dependencies, I wanted an access to a system similar to the Python WeakKeyDictionary class : Mapping class that references keys weakly. Entries in the dictionary will be > discarded when there is no longer a strong reference to the key. This can be > used to associate additional data with an object owned by other parts of an > application without adding attributes to those objects. I drafted a small 'weak_key_map' class based on boost weak_ptr, shared_ptr deleters, and a base class enabling classes to be used as keys in the weak_key_map. A small use case example is shown after, and source of weak_key_map & co are attached. I was wandering if someone had experience to share about a similar system ? For a first draft, it already serves me well - but, I'm not very happy with to "pollute" keys with the base class 'enable_master_ptr'... Any idea to improve all this ? Best regards, Nicolas. int Master_count = 0; class Master : public mgd::enable_master_ptr<Master> { public: Master() { Master_count++; } ~Master() { Master_count--; } }; int Dependent_count = 0; class Dependent : boost::noncopyable { public: Dependent() { Dependent_count++; } ~Dependent() { Dependent_count--; } }; BOOST_AUTO_TEST_CASE( test_weak_key_map_lifeTime ) { typedef boost::shared_ptr<Dependent> value_t; typedef mgd::weak_key_map<Master, value_t> map_t; map_t map; { Master master1; BOOST_CHECK( !map[&master1] ); map[&master1] = value_t( new Dependent ); BOOST_CHECK( map[&master1] ); { Master master2; map[&master2] = value_t( new Dependent ); BOOST_REQUIRE_EQUAL( Master_count, 2 ); BOOST_REQUIRE_EQUAL( Dependent_count, 2 ); } map[&master1] = value_t( new Dependent ); BOOST_REQUIRE_EQUAL( Master_count, 1 ); BOOST_REQUIRE_EQUAL( Dependent_count, 1 ); map.clear(); BOOST_REQUIRE_EQUAL( Master_count, 1 ); BOOST_REQUIRE_EQUAL( Dependent_count, 0 ); } BOOST_REQUIRE_EQUAL( Master_count, 0 ); BOOST_REQUIRE_EQUAL( Dependent_count, 0 ); }

4 6

Need advice on std::queue syncronization using boost::mutex - maybe a bug in pthread?
by Ilya Kalujny 13 Dec '08

13 Dec '08

Hello All! I`d like to ask for your kind advice regarding boost::mutex behaviour. I dont see what i`m doing wrong here. The issue is that at some point a mutex used to syncronize access to std::queue becomes locked on it's own, despite being explicitly unlocked before. I can repeat this more or less consistently. I triple checked the logic behind code and it seems correct to me. Here is the code and some explanations (i build and test under windows): Class itself: #pragma once #include <queue> // simple std::queue based boost::mutex syncronized queue template <typename T> class SyncedQueue : boost::noncopyable { private: std::queue<T> queue; // this is intended to be locked when queue is empty boost::mutex emptyIndicator; //this is intended to be locked when queue is being modified boost::mutex accessGuard; public: SyncedQueue(const SyncedQueue<T> &) { //no copy constructor since we got mutexes } SyncedQueue() { // Queue is empty at start emptyIndicator.lock(); } bool push ( T object ) { accessGuard.lock(); queue.push(object); // if someone has been waiting for data to become available in queue - let them go on emptyIndicator.unlock(); accessGuard.unlock(); return true; } bool pop ( T& object ) { // See if data is available, wait to aquire lock otherwise emptyIndicator.lock(); // OK, somethings in the queue now, we can go on accessGuard.lock(); object = queue.front(); queue.pop(); // If there is anything left in the queue - release emptyIndicator to notify other poppers that they can go on if (queue.size() > 0) { emptyIndicator.unlock(); } accessGuard.unlock(); return true; } }; Here is the test Code: #include "stdafx.h" #include <string> #include <iostream> #include <boost/thread.hpp> #include <boost/shared_ptr.hpp> #include <include/threadpool.hpp> #include "SyncedQueue.h" // global variable for the queue SyncedQueue< boost::shared_ptr < std::string > > syncedQueue; void testWriteQueue() { for (int i = 0; i < 100; i++) { char szBuff[128]; boost::shared_ptr< std::string > msgPtr; std::string tmpString = "Message"; tmpString += itoa(i,szBuff, 10); msgPtr.reset(new std::string(tmpString)); syncedQueue.push(msgPtr); std::cout << "Sent " << msgPtr->c_str() << std::endl; } // After this thread completes, reader thread sometimes deadlocks! std::cout << "Sent all" << std::endl; } void testReadQueue() { int recievedmessnum = 0; while(recievedmessnum != 100) { boost::shared_ptr< std::string > recievedMsgPtr; // After this writer thread completes, it sometimes sometimes deadlocks trying to aqurie emptyIndicator! syncedQueue.pop(recievedMsgPtr); std::cout << "Recieved " << recievedMsgPtr->c_str() << std::endl; recievedmessnum++; } std::cout << "Recieved all" << std::endl; } int main(int argc, char** argv) { using namespace boost::threadpool; pool tp(2); tp.schedule(&testWriteQueue); tp.schedule(&testReadQueue); tp.wait(); std::cout << "Test complete" << std::endl; } Thanks in advance, Ilya.

2 2