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[array][smart_ptr] Using shared_ptr vs shared_array for a boost::array
by Ryan McConnehey 12 Aug '10

12 Aug '10

I currently have a boost::array in a share_ptr. This compiles and doesn't cause memory leaks. Should I expect memory leaks since I'm not using shared_array? Should I bother and convert over to shared_array? I would have expected a problem with boost::array and shared_ptr but I'm unsure about expected behavior. Ryan

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Why use 'functional composition' with boost::bind
by Wolfram Brenig 12 Aug '10

12 Aug '10

Hi, as a casual/newbie boost-user I'm trying to come to grips with why/when nested functional composition with boost::bind might be of help - following Karlsson's book, in its fifth printing. ---------------------- 1) It seems that he suggests, that if one is into doing something like T faa(int); T foo(const& T); int i; vector<T> v(10); // container for(i=0; i<10; i++) { v[i] = faa(i); // set it v[i] = foo(v[i]); // operate on it } then instead of the 'old style' for-loops it would be more desirable to use 'STL style' algorithms with the functors created from boost::bind, say like transform(v.begin(),v.end(),boost::bind(&foo,_1)); instead of the 2nd line in the previous for-loop, a.s.o. ---------------------- 2) Then, it is suggested furthermore that if foo() is a (simple?) nested function, say T=double and, double foo(double x) { return 2*x; } then one should do 'functional composition', i.e. create the functor for the previous point 1) by boost::bind(std::multiplies<double>(),2,_1) (Karlsson has this example on adding and subtracting 10%.) ----------------------- Now, my question is, if such nested construction of functors at the call site, which is suggested also in the 'Bind Summary' in Karlsson's book, will actually lead to code which has no relevant performance loss as compared to 'old-style' for-loops? To check this, I do something rather simple (simplistic?). Namely, I take a vector of some size, then I fill it with random doubles between 0 and M_PI, then (stupid me) I test if sin(v[i])^2 + cos([i])^2 = 1 for each element of the vector. The code is attached. I do this many many times and measure the runtime. I do this for two cases: case 1: with old-style for loops case 3: with STL algorithms and boost::bind At least for this little program, the old-style code is faster by roughly a factor of 2 as compared to the boost::bind approach. (compiled with gcc version 4.3.2 and optimized) Case 2 just to show that this is not due to more sin()/cos() function calls within the nested functor, since it is also a factor of 2 faster than then the boost variant. So, in conclusion: when/how should I really use functional composition? wb --------------------------------- #include <iostream> #include <vector> #include <math.h> #include <algorithm> #include "boost/lambda/bind.hpp" #include <assert.h> #include <time.h> using namespace std; using namespace boost; using namespace boost::lambda; int main() { int in; unsigned n(1000),i,l; double x,y,t; vector<double> v(n); clock_t start, stop; cin >> in; // tell me which case to check switch(in) { case 0: // Check how much time is lost in loops and math // --------------------------------------------------------------------------- t = 0.0; assert((start = clock())!=-1); for(l=0;l<10000;l++) { for(i=0;i<n;i++) { x= (random()*M_PI)/RAND_MAX; x = sin(v[i]); x = x*x; y = cos(v[i]); y = y*y; x = x + y; } } stop = clock(); t = (double) (stop-start)/CLOCKS_PER_SEC; cout << t << endl; break; case 1: // Time for old-style for-loops // --------------------------------------------------------------------------- t = 0.0; assert((start = clock())!=-1); for(l=0;l<10000;l++) { for(i=0;i<n;i++) { v[i] = (random()*M_PI)/RAND_MAX; x = sin(v[i]); x = x*x; y = cos(v[i]); y = y*y; v[i] = x + y; } } stop = clock(); t = (double) (stop-start)/CLOCKS_PER_SEC; cout << t << endl; break; case 2: // Time for old-style for-loops and unnecessarily many sin/cos calls // --------------------------------------------------------------------------- t = 0.0; assert((start = clock())!=-1); for(l=0;l<10000;l++) { for(i=0;i<n;i++) { v[i] = (random()*M_PI)/RAND_MAX; v[i] = sin(v[i])*sin(v[i])+cos(v[i])*cos(v[i]); } } stop = clock(); t = (double) (stop-start)/CLOCKS_PER_SEC; cout << t << endl; break; case 3: // Time needed with nested boost::bind and STL iteration over container // --------------------------------------------------------------------------- t = 0.0; assert((start = clock())!=-1); for(l=0;l<10000;l++) { generate(v.begin(),v.end(), bind(multiplies<double>(), bind(&random), M_PI/RAND_MAX)); transform(v.begin(),v.end(),v.begin(), bind(plus<double>(), bind(multiplies<double>(),bind(sin,_1),bind(sin,_1)), bind(multiplies<double>(),bind(cos,_1),bind(cos,_1)) ) ); } stop = clock(); t = (double) (stop-start)/CLOCKS_PER_SEC; cout << t << endl; break; } return EXIT_SUCCESS; }

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shared_ptr vs pass object by reference
by Max S. Kaznady 11 Aug '10

11 Aug '10

If I can pass the object by reference to a function, then is there a need to use shared pointers? I demonstrated 3 ways of passing by reference below, but my main concern is just passing a shared_ptr by value VS passing an object reference. #include<iostream> #include <boost/numeric/ublas/matrix.hpp> #include <boost/numeric/ublas/io.hpp> #include <boost/shared_ptr.hpp> // If I can just pass an object like this, this do I really need to use shared pointers? void pass_obj_ref(boost::numeric::ublas::matrix<double> &m) { for (unsigned i = 0; i < m.size1(); ++i) for (unsigned j = 0; j < m.size2(); ++j) m(i, j) = 3 * i + j; } // This is the correct way to pass a pointer, because we create a copy of the pointer inside // the function and we cannot do something to the pointer outside of the scope of the function call void pass_ptr_by_val( boost::shared_ptr<boost::numeric::ublas::matrix<double> > const m) { for (unsigned i = 0; i < m->size1(); ++i) for (unsigned j = 0; j < m->size2(); ++j) (*m)(i, j) = 3 * i + j; } // This is not good since we can modify the pointer within the function, and then // another developer wouldn't know what to do after the function call void pass_ptr_by_ref( boost::shared_ptr<boost::numeric::ublas::matrix<double> > const &m) { for (unsigned i = 0; i < m->size1(); ++i) for (unsigned j = 0; j < m->size2(); ++j) (*m)(i, j) = 3 * i + j; } int main(void) { unsigned s1 = 10, s2 = 20; // regular matrix boost::numeric::ublas::matrix<double> m1(s1, s2); // pass pointer by value boost::shared_ptr<boost::numeric::ublas::matrix<double> > m2( new boost::numeric::ublas::matrix<double>(s1, s2)); // pass pointer by reference boost::shared_ptr<boost::numeric::ublas::matrix<double> > m3( new boost::numeric::ublas::matrix<double>(s1, s2)); pass_obj_ref(m1); pass_ptr_by_val(m2); pass_ptr_by_ref(m3); std::cout << m1 << std::endl; std::cout << *m2 << std::endl; std::cout << *m3 << std::endl; }

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[Thread] Writer/Reader strange scheduling
by Gaetano Mendola 11 Aug '10

11 Aug '10

Hi all, I'm in need to have a reader/writer mutex with no starvation (I'd say a fair mutex), before to make a my own implementation I have checked the boost one to see if it makes starvation or not, and I'm a bit puzzled about the behave: I'm experiencing this: reader 1 start ... writer 1 running ... reader 2 start ... writer 2 running ... writer 1 start << blocked reader 3 start << blocked reader 4 start << blocked until now it seems that reader 3 and reader 4 are waiting because there is a writer waiting and then the writer will run before reader 3 and 4, unfortunately this is not the case, the execution continues like this: reader 1 ends reader 2 ends ... writer 3 running ... ... writer 4 running ... reader 3 ends reader 4 ends ... writer 1 running ... writer 1 ends isn't that a waste? Why make reader 3 and 4 waiting and then make those running before the writer? The code to reproduce that is at the end. Regards Gaetano Mendola #include <iostream> #include <boost/thread.hpp> typedef boost::shared_mutex TMutex; TMutex theMutex; struct Writer { Writer(const size_t anId) : theId(anId) { } void operator()() { std::cout << "writer " << theId << " start" << std::endl; boost::unique_lock<TMutex> myLock(theMutex); std::cout << " ... writer " << theId << " running ..." << std::endl; ::sleep(7); std::cout << "writer " << theId << " ends" << std::endl; } size_t theId; }; struct Reader { Reader(const size_t anId) : theId(anId) { } void operator()() { std::cout << "reader " << theId << " start" << std::endl; boost::shared_lock<TMutex> myLock(theMutex); std::cout << " ... writer " << theId << " running ..." << std::endl; ::sleep(7); std::cout << "reader " << theId << " ends" << std::endl; } size_t theId; }; int main (int argc, char** argv) { Reader r1(1), r2(2), r3(3), r4(4); Writer w(1); boost::thread myR1(boost::ref(r1)); ::sleep(1); boost::thread myR2(boost::ref(r2)); ::sleep(1); boost::thread myW1(boost::ref(w)); ::sleep(1); boost::thread myR3(boost::ref(r3)); ::sleep(1); boost::thread myR4(boost::ref(r4)); myW1.join(); myR1.join(); myR2.join(); myR3.join(); myR4.join(); }

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[Boost.Thread - promise::lazy_init()] core dump when sharing promise between threads
by Thijs Terlouw 11 Aug '10

11 Aug '10

I am experiencing core-dumps when sharing a boost::promise between two threads. Full core-dump at the bottom. My guess: When one thread does promise.set_value(), I found that the set_value() function of the promise class will execute lazy_init() and then lock a guard. The other tread at the same time might execute promise.get_future() which will also do a lazy_init(). It seems this introduces a race-condition between the get_future() call and the set_value() call: the local future_ptr in the promise class might be reset() while it's being used? This has resulted in some coredumps (. If I change /usr/local/boost_1_43_0/boost/thread/future.hpp to call lazy_init() in the constructor of promise (around line 919, though it will not be lazy anymore), the crashes disappear. What's the right solution to this? Is it a bug in boost::promise or do I use it wrong? My use case: I am writing an asynchronous library to be used inside synchronous code. I use Boost.Asio + Boost.Thread futures/promises. One thread (Asio) sends + receives packets. It will return a boost::shared_ptr<packet_promise> where packet_promise is a boost::promise<PacketType> when doing a write. When the Asio thread receives, I do a set_value() to the promise. The main thread, the one that did the request, will receive the shared_ptr to the packet_promise and then execute get_value() on the promise. My system: Boost 1.43.0. Linux 2.6.16.21-0.8 g++ (GCC) 4.1.0 (SUSE Linux) ======================= full core-dump without calling the lazy_init() inside the promise's constructor: #0 0xffffe410 in __kernel_vsyscall () #1 0xb7c377d0 in raise () from /lib/libc.so.6 #2 0xb7c38ea3 in abort () from /lib/libc.so.6 #3 0xb7c3101b in __assert_fail () from /lib/libc.so.6 #4 0x080f68b3 in ~mutex (this=0x81c8090) at /usr/local/boost_1_43_0/boost/thread/pthread/mutex.hpp:46 #5 0x080fc375 in ~future_object_base (this=0x81c8080) at /usr/local/boost_1_43_0/boost/thread/future.hpp:104 #6 0x080fc44c in ~future_object (this=0x81c8080) at /usr/local/boost_1_43_0/boost/thread/future.hpp:290 #7 0x080cbd62 in boost::checked_delete<boost::detail::future_object<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> > > (x=0x81c8080) at /usr/local/boost_1_43_0/boost/checked_delete.hpp:34 #8 0x080cf724 in boost::detail::sp_counted_impl_p<boost::detail::future_object<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> > >::dispose (this=0x81a2f40) at /usr/local/boost_1_43_0/boost/smart_ptr/detail/sp_counted_impl.hpp:78 #9 0x080c4586 in boost::detail::sp_counted_base::release (this=0x81a2f40) at /usr/local/boost_1_43_0/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:145 #10 0x080c45cc in ~shared_count (this=0xb4bc5b94) at /usr/local/boost_1_43_0/boost/smart_ptr/detail/shared_count.hpp:217 #11 0x080c56cc in ~shared_ptr (this=0xb4bc5b90) at /usr/local/boost_1_43_0/boost/smart_ptr/shared_ptr.hpp:169 #12 0x080d87c5 in boost::shared_ptr<boost::detail::future_object<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> > >::reset<boost::detail::future_object<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> > > (this=0x8250230, p=0x823c780) at /usr/local/boost_1_43_0/boost/smart_ptr/shared_ptr.hpp:392 #13 0x080fc8cf in boost::promise<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> >::lazy_init ( this=0x8250230) at /usr/local/boost_1_43_0/boost/thread/future.hpp:909 #14 0x080fc908 in boost::promise<lib_async::CQunPacket<lib_async::CQunEnvelope, lib_async::CQunHeader, lib_async::CQunBody> >::get_future (this=0x8250230) at /usr/local/boost_1_43_0/boost/thread/future.hpp:978 #15 0x080fd38e in SQunSession::recvAll (this=0xb4bc62dc, error=@0xb4bc618e, TimeoutMs=500) at /data/home/thijs/git/yaaf/public/libasync/worker_async_demo.cpp:101 #16 0x080fd828 in AsyncDemoWorker::do_my_special_thing (this=0x81b2080, session=@0xb4bc62dc) at /data/home/thijs/git/yaaf/public/libasync/worker_async_demo.cpp:240 #17 0x080fe7d6 in AsyncDemoWorker::onRequest (this=0x81b2080, sock=@0x819e3f8) at /data/home/thijs/git/yaaf/public/libasync/worker_async_demo.cpp:189 #18 0xb7f61da8 in yaaf::BaseWorker::run (this=0x81b2080) at /data/home/thijs/git/yaaf/public/libyaaf/yaaf_worker.cpp:68 #19 0xb7f5d8cf in yaaf::Context::thread_entry_point (ctx=0x81b2088) at /data/home/thijs/git/yaaf/public/libyaaf/yaaf_context.cpp:287 #20 0xb7f7934b in start_thread () from /lib/libpthread.so.0 #21 0xb7ccc65e in clone () from /lib/libc.so.6 line 101 in worker_async_demo.cpp looks like this: 100: packet_promise_ptr ppp_temp = (*it).first; //copy of shared pointer, stored in a map 101: packet_future pf = ppp_temp->get_future(); //core-dump here Thijs

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[boostcon] Where is the viterbi library from boostcon 2009?
by Ravi 11 Aug '10

11 Aug '10

Hello, Does anyone have a copy of the Viterbi (dynamic programming) library from boostcon 2009? My google-fu is insufficient to locate it. An email to the author's email address from the boostcon presentation failed to elicit any response. In case anyone is wondering which talk from boostcon prompted my request, here is a link: http://www.mefeedia.com/watch/32045638 Ravi

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weak_from_this
by Hite, Christopher 11 Aug '10

11 Aug '10

shared_from_this contains a weak_ptr. Why not implement a weak_from_this() member function? Upgrading and downgrading a shared_ptr costs expensive atomic ops. I've got some setup code that just gives weak_ptr's to boost::singals2::slot::track(). Is this a valid (and simple) feature request? Chris

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[boost] [chrono] v0.4.5 Documentation update + warnings removal + bug fixes
by vicente.botet 10 Aug '10

10 Aug '10

Hi, I have made some minor modifications to the Boost.Chrono library as requested on these mailing lists. The implementaton is stable. Waiting for the review I plan to add yet a lightweight stopwatch, as suggested by Tom Tan on a personal mail, which stores a reference to a generalization of the Clock duration or an accumulator of the Clock duration. I'll concentrate also in improving the documentation and the tests. Anthony Williams will be the review manager and I hope we could find a date soon. Even if the review's date is not annonced yet, it will be great if some of you make a pre-review, so the conflicting issues are managed before the review. The library can be downloaded from http://www.boostpro.com/vault/index.php?action=downloadfile&filename=chrono… and the documentation is online on the sandbox http://svn.boost.org/svn/boost/sandbox/chrono/libs/chrono/doc/html/index.ht…. New Features since v0.4.3: Version 0.4.5, July 6, 2010 Documentation update Documentation a.. Overview rewriting b.. Added missing thread_clock reference. c.. How to implement a thread_clock tutorial removed. d.. References section renamed to External Resources. e.. Added links to source examples. f.. Added links between Models and Concepts. g.. Added macros descriptions. h.. Cleanup. Bug Fixes a.. Valgrind fixes: "Conditional jump or move depends on uninitialised value(s)" b.. Take care of Boost.System break on version 1.44 c.. gcc.4.4 "warning: suggest parentheses around '&&' within '||' " removal. Version 0.4.4, February 22, 2010 Warning fixes Bug Fixes a.. scoped_suspend warning removal b.. error_code management completed _____________________ Vicente Juan Botet Escribá http://viboes.blogspot.com/

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[Thread] Missing #includes in future.hpp
by Andrew Holden 10 Aug '10

10 Aug '10

I noticed that my code that uses futures wouldn't compile until I added the following two lines to future.hpp: #include <boost/thread/mutex.hpp> #include <boost/thread/condition_variable.hpp> I am wondering if this is an oversight, or if there is a specific reason these files weren't included in future.hpp

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[property tree][program options] io with Windows Registry?
by Jeff Flinn 10 Aug '10

10 Aug '10

I've see mailing list archives mention supporting Windows Registry, but can not find any mention in the docs for either of these libs. Is there support yet? What I'm hoping to find is portable support for preferences on both Windows registry and Mac plists. Thanks, Jeff

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