August 2010 - Boost-users - lists.preview.boost.org

[Spirit] dereferencing type-punned pointer will break strict-aliasing rules
by Roland Bock 12 Aug '10

12 Aug '10

Hi, compiling the attached example with gcc-4.4.3 (Ubuntu 10.4, 64bit) with -Wall -O3 leads to a long warning message (second attachment), culminating in boost/1.44/include/boost/function/function_base.hpp:321: warning: dereferencing type-punned pointer will break strict-aliasing rules boost/1.44/include/boost/function/function_base.hpp:325: warning: dereferencing type-punned pointer will break strict-aliasing rules I wonder how I could avoid this without -fno-strict-aliasing or -Wno-strict-aliasing? Thanks and regards, Roland

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[lambda][optional] Accessing an optional variable through lambda
by Ryan McConnehey 12 Aug '10

12 Aug '10

I'm trying to create a stream operator for a list of DataPoint objects. I can't get the correct boost::lambda syntax to access what the optional is containing. Could someone tell me what I'm doing wrong? Ryan struct DataPoint { boost::optional<double> m_Time; }; std::ostream & operator<<(std::ostream & stream, std::list<DataPoint> const& points) { namespace bll = boost::lambda; std::for_each( points.begin(), points.end(), stream << bll::bind(&boost::optional<double>::get, bll::bind(&DataPoint::m_Time, bll::_1)) << bll::constant(" ")); //Would prefer to do something like this "*bll::bind(&DataPoint::m_Time, bll::_1)". This gives me quite the compile //error. Is there a way to use indirection or do I need to bind to a optional method to get access? return stream; }

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multi_array of triangular_matrices runtime error
by Max S. Kaznady 12 Aug '10

12 Aug '10

Hello, I just noticed a strange runtime error, and I think that it should be addressed by the developers. Consider the following seemingly equivalent statements, in terms of functionality: using namespace boost::numeric::ublas; using namespace boost::multi_array; const unsigned A_dim = 4; multi_array<triangular_matrix<double, lower> , A_dim>::extent_gen extents; 1) multi_array<triangular_matrix<double, lower> , A_dim> A(extents[2][2][2][2]); 2) multi_array<triangular_matrix<double, lower> , A_dim> A; A = multi_array<triangular_matrix<double, lower> , A_dim>(extents[2][2][2][2]); Add either statement 1 or 2. Both compile just fine with GCC 4.4, but the second statement, last line, produces a runtime error: main: /usr/local/boost/include/boost/multi_array/multi_array_ref.hpp:487: boost::multi_array_ref<T, NumDims>& boost::multi_array_ref<T, NumDims>::operator=(const ConstMultiArray&) [with ConstMultiArray = boost::multi_array<boost::numeric::ublas::triangular_matrix<double, boost::numeric::ublas::basic_lower<long unsigned int>, boost::numeric::ublas::basic_row_major<long unsigned int, long int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > >, 4ul, std::allocator<boost::numeric::ublas::triangular_matrix<double, boost::numeric::ublas::basic_lower<long unsigned int>, boost::numeric::ublas::basic_row_major<long unsigned int, long int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > > > >, T = boost::numeric::ublas::triangular_matrix<double, boost::numeric::ublas::basic_lower<long unsigned int>, boost::numeric::ublas::basic_row_major<long unsigned int, long int>, boost::numeric::ublas::unbounded_array<double, std::allocator<double> > >, long unsigned int NumDims = 4ul]: Assertion `std::equal(other.shape(),other.shape()+this->num_dimensions(), this->shape())' failed. I KNOW that I can resolve the issue with shared_ptr, having multi_array store shared pointers to the matrix A. However, if I understand correctly, then shouldn't the second statement either not compile or compile and work fine? From what I understand the added functionality of multi_arrays is that they can store other arrays, maybe I'm wrong? Thanks, Max

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TypeError: No registered converter was able to extract a C++ pointer to type char from this Python object of type str
by Brian Ray 12 Aug '10

12 Aug '10

Hello: I think I am experience a build problem here but not really sure; nonetheless, below is a simple example that illustrates my problem. Any idea what I might be doing wrong. I am using boost_1_43_0 built with gcc 4.2.1 on i686 running darwin. Please note that the PyRun_SimpleString("import sys"); does not error at all. The error comes from when the call to import(). I am not sure if this is a clue or not but gdb seems not to know what line it is on. I am guessing it is just confused because of all the inlines. I suspect this is a linking issues of some sort. However I did check that they are all linking to the correct location. Why does it convert the const char * to a str in the first place. Seems to be thrashing around a bit. -- Brian /// contents of boost_python_issue.cpp #include <boost/python.hpp> using namespace boost::python; int main(int argc, char **argv) { Py_Initialize(); try { PyRun_SimpleString("import sys"); // This raises exception object sys = import("sys"); } catch (boost::python::error_already_set) { PyErr_Print(); } Py_Finalize(); } // Compiled with 'g++ -I. -I/usr/include -I/usr/local/include -I../../includes/python2_5_1 -g -L/usr/local/lib boost_python_issue.cpp -lboost_system -lboost_python -lm -lpython2.5 -o boost_python_issue' Output from gdb: (gdb) break main Breakpoint 1 at 0x100001319: file boost_python_issue.cpp, line 9. (gdb) r Starting program: /Project/zephyr/src/Composer/boost_python_issue Reading symbols for shared libraries .++++++++..... done Breakpoint 1, main (argc=1, argv=0x7fff5fbff6d8) at boost_python_issue.cpp:9 9 Py_Initialize(); (gdb) s 11 PyRun_SimpleString("import sys"); (gdb) 13 object sys = import("sys"); (gdb) boost::python::str::str (this=0x7fff5fbff690, s=0x10000169d "sys") at str.hpp:150 150 str(const char* s) : base(s) {} // new str (gdb) boost::python::detail::str_base::str_base (this=0x7fff5fbff690, s=0x10000169d "sys") at libs/python/src/str.cpp:39 39 )) (gdb) object [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/object_core.hpp:534 Line number 534 out of range; errors.hpp has 55 lines. (gdb) expect_non_null<PyObject> [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/errors.hpp:43 44 if (x == 0) (gdb) object [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/object_core.hpp:513 534 : object_base(expect_non_null((PyObject*)p)) (gdb) object_base [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/object_core.hpp:513 513 : m_ptr(p) (gdb) boost::python::detail::str_base::str_base (this=0x7fff5fbff690, s=<value temporarily unavailable, due to optimizations>) at libs/python/src/str.cpp:40 40 {} (gdb) 0x000000010000154d in boost::python::str::str (this=0x7fff5fbff690, s=0x10000169d "sys") at str.hpp:150 150 str(const char* s) : base(s) {} // new str (gdb) boost::python::import (name=@0x7fff5fbff690) at libs/python/src/import.cpp:19 19 char *n = python::extract<char *>(name); (gdb) extract [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/extract.hpp:156 156 # else (gdb) boost::python::api::object_base::ptr () at /Users/bray/sources/boost_1_43_0/boost/python/object_core.hpp:542 543 return m_ptr; (gdb) extract [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/extract.hpp:216 156 : base(o.ptr()) (gdb) extract_pointer [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/extract.hpp:216 219 ) (gdb) boost::python::converter::get_lvalue_from_python (source=0x1005cb1e0, converters=@0x100409500) at libs/python/src/converter/from_python.cpp:128 128 void* x = objects::find_instance_impl(source, converters.target_type); (gdb) boost::python::objects::find_instance_impl (inst=0x1005cb1e0, type={<boost::totally_ordered<boost::python::type_info,boost::python::type_info,boost::detail::empty_base<boost::python::type_info>,boost::detail::false_t>> = {<boost::totally_ordered1<boost::python::type_info,boost::detail::empty_base<boost::python::type_info> >> = {<boost::less_than_comparable1<boost::python::type_info,boost::equality_comparable1<boost::python::type_info, boost::detail::empty_base<boost::python::type_info> > >> = {<boost::equality_comparable1<boost::python::type_info,boost::detail::empty_base<boost::python::type_info> >> = {<boost::detail::empty_base<boost::python::type_info>> = {<No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}, <No data fields>}, m_base_type = 0x7fff885a066c "c"}, null_shared_ptr_only=false) at libs/python/src/object/class.cpp:485 485 if (Py_TYPE(Py_TYPE(inst)) != &class_metatype_object) (gdb) 490 for (instance_holder* match = self->objects; match != 0; match = match->next()) (gdb) 497 } (gdb) boost::python::converter::get_lvalue_from_python (source=0x1005cb1e0, converters=@0x100409500) at libs/python/src/converter/from_python.cpp:129 129 if (x) (gdb) 132 lvalue_from_python_chain const* chain = converters.lvalue_chain; (gdb) 133 for (;chain != 0; chain = chain->next) (gdb) 135 void* r = chain->convert(source); (gdb) boost::python::converter::(anonymous namespace)::convert_to_cstring (obj=0x1005cb1e0) at libs/python/src/converter/builtin_converters.cpp:46 46 return PyString_Check(obj) ? PyString_AsString(obj) : 0; (gdb) 47 } (gdb) boost::python::converter::get_lvalue_from_python (source=0x1005cb1e0, converters=<value temporarily unavailable, due to optimizations>) at libs/python/src/converter/from_python.cpp:136 136 if (r != 0) (gdb) 132 lvalue_from_python_chain const* chain = converters.lvalue_chain; (gdb) 133 for (;chain != 0; chain = chain->next) (gdb) 140 } (gdb) 0x00000001001a1128 in extract_pointer [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/extract.hpp:219 219 ) (gdb) boost::python::import (name=<value temporarily unavailable, due to optimizations>) at libs/python/src/import.cpp:19 19 char *n = python::extract<char *>(name); (gdb) boost::python::extract<char*>::operator char* () at /Users/bray/sources/boost_1_43_0/boost/python/extract.hpp:138 138 return (*this)(); (gdb) boost::python::converter::extract_pointer<char*>::operator() () at extract.hpp:231 232 if (m_result == 0 && m_source != Py_None) (gdb) boost::python::converter::extract_pointer<char*>::operator() () at extract.hpp:233 233 (throw_no_pointer_from_python)(m_source, registered_pointee<Ptr>::converters); (gdb) boost::python::converter::throw_no_pointer_from_python (source=0x1005cb1e0, converters=@0x100409500) at libs/python/src/converter/from_python.cpp:256 256 (throw_no_lvalue_from_python)(source, converters, "pointer"); (gdb) 257 } (gdb) boost::python::converter::throw_no_pointer_from_python (source=0x1005cb1e0, converters=@0x100409500) at libs/python/src/converter/from_python.cpp:256 256 (throw_no_lvalue_from_python)(source, converters, "pointer"); (gdb) boost::python::converter::(anonymous namespace)::throw_no_lvalue_from_python (source=0x1005cb1e0, converters=@0x100409500, ref_type=0x1001a8e55 "pointer") at libs/python/src/converter/from_python.cpp:201 201 void throw_no_lvalue_from_python(PyObject* source, registration const& converters, char const* ref_type) (gdb) 215 )); (gdb) boost::python::type_info::name () at /Users/bray/sources/boost_1_43_0/boost/python/type_id.hpp:156 156 { (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:116 116 static mangling_map demangler; (gdb) 121 , compare_first_cstring()); (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::end () at /usr/include/c++/4.2.1/bits/stl_vector.h:349 349 inline bool (gdb) __normal_iterator [inlined] () at /usr/include/c++/4.2.1/bits/stl_iterator.h:654 817 { return __lhs.base() - __rhs.base(); } (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::end () at /usr/include/c++/4.2.1/bits/stl_vector.h:331 331 { return iterator(this->_M_impl._M_start); } (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:121 121 , compare_first_cstring()); (gdb) lower_bound<__gnu_cxx::__normal_iterator<std::pair<const char*, const char*>*, std::vector<std::pair<const char*, const char*>, std::allocator<std::pair<const char*, const char*> > > >, std::pair<const char*, const char*>, boost::python::<unnamed>::compare_first_cstring> [inlined] () at /usr/include/c++/4.2.1/bits/stl_algo.h:98 98 return __last - __first; (gdb) operator-<std::pair<const char*, const char*>*, std::vector<std::pair<const char*, const char*>, std::allocator<std::pair<const char*, const char*> > > > [inlined] () at /usr/include/c++/4.2.1/bits/stl_iterator_base_funcs.h:119 119 std::__iterator_category(__first)); (gdb) __distance<__gnu_cxx::__normal_iterator<std::pair<const char*, const char*>*, std::vector<std::pair<const char*, const char*>, std::allocator<std::pair<const char*, const char*> > > > > [inlined] () at /usr/include/c++/4.2.1/bits/stl_iterator_base_funcs.h:2948 Line number 2948 out of range; stl_iterator_base_funcs.h has 182 lines. (gdb) distance<__gnu_cxx::__normal_iterator<std::pair<const char*, const char*>*, std::vector<std::pair<const char*, const char*>, std::allocator<std::pair<const char*, const char*> > > > > [inlined] () at /usr/include/c++/4.2.1/bits/stl_iterator.h:116 156 __i += __n; (gdb) lower_bound<__gnu_cxx::__normal_iterator<std::pair<const char*, const char*>*, std::vector<std::pair<const char*, const char*>, std::allocator<std::pair<const char*, const char*> > > >, std::pair<const char*, const char*>, boost::python::<unnamed>::compare_first_cstring> [inlined] () at /usr/include/c++/4.2.1/bits/stl_algo.h:2952 2952 while (__len > 0) (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:121 121 , compare_first_cstring()); (gdb) 123 if (p == demangler.end() || strcmp(p->first, mangled)) (gdb) 128 ); (gdb) 132 if (status == -1) (gdb) 143 : keeper.p; (gdb) 152 if (cxxabi_cxa_demangle_is_broken() (gdb) cxxabi_cxa_demangle_is_broken [inlined] () at /Users/bray/sources/boost_1_43_0/libs/python/src/converter/type_id.cpp:94 97 if (!was_tested) { (gdb) 99 free_mem keeper(cxxabi::__cxa_demangle("b", 0, 0, &status)); (gdb) 100 was_tested = true; (gdb) 101 if (status == -2 || strcmp(keeper.p, "bool") != 0) { (gdb) 103 } (gdb) ~free_mem [inlined] () at /Users/bray/sources/boost_1_43_0/libs/python/src/converter/type_id.cpp:86 87 std::free(p); (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:152 152 if (cxxabi_cxa_demangle_is_broken() (gdb) 183 p = demangler.insert(p, std::make_pair(mangled, demangled)); (gdb) 331 { return iterator(this->_M_impl._M_start); } (gdb) 183 p = demangler.insert(p, std::make_pair(mangled, demangled)); (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::insert () at /usr/include/c++/4.2.1/bits/vector.tcc:93 95 if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage (gdb) 102 _M_insert_aux(__position, __x); (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_insert_aux (this=0x1001bfd40, __position={_M_current = 0x0}, __x=@0x7fff5fbff5a0) at vector.tcc:245 245 _M_insert_aux(iterator __position, const _Tp& __x) (gdb) 247 if (this->_M_impl._M_finish != this->_M_impl._M_end_of_storage) (gdb) 260 const size_type __old_size = size(); (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::size () at /usr/include/c++/4.2.1/bits/stl_vector.h:400 400 { return size_type(this->_M_impl._M_finish - this->_M_impl._M_start); } (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_insert_aux (this=0x1001bfd40, __position={_M_current = 0x0}, __x=@0x7fff5fbff5a0) at vector.tcc:261 261 if (__old_size == this->max_size()) (gdb) 267 size_type __len = __old_size != 0 ? 2 * __old_size : 1; (gdb) 88 if (__builtin_expect(__n > this->max_size(), false)) (gdb) 91 return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp))); (gdb) 275 __new_finish = (gdb) __uninitialized_copy_a<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*, std::pair<const char*, const char*> > [inlined] () at /usr/include/c++/4.2.1/bits/stl_uninitialized.h:114 114 _Is_POD()); (gdb) __uninitialized_copy_aux<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*> [inlined] () at stl_uninitialized.h:254 254 { return std::uninitialized_copy(__first, __last, __result); } (gdb) uninitialized_copy<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*> [inlined] () at stl_uninitialized.h:254 254 { return std::uninitialized_copy(__first, __last, __result); } (gdb) __gnu_cxx::new_allocator<std::pair<char const*, char const*> >::construct () at /usr/include/c++/4.2.1/ext/new_allocator.h:107 107 { ::new(__p) _Tp(__val); } (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_insert_aux (this=0x1001bfd40, __position={_M_current = 0x0}, __x=@0x7fff5fbff5a0) at vector.tcc:280 280 ++__new_finish; (gdb) 281 __new_finish = (gdb) __uninitialized_copy_a<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*, std::pair<const char*, const char*> > [inlined] () at /usr/include/c++/4.2.1/bits/stl_uninitialized.h:114 114 _Is_POD()); (gdb) __uninitialized_copy_aux<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*> [inlined] () at stl_uninitialized.h:254 254 { return std::uninitialized_copy(__first, __last, __result); } (gdb) uninitialized_copy<std::pair<const char*, const char*>*, std::pair<const char*, const char*>*> [inlined] () at stl_uninitialized.h:254 254 { return std::uninitialized_copy(__first, __last, __result); } (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_insert_aux (this=0x1001bfd40, __position={_M_current = 0x0}, __x=<value temporarily unavailable, due to optimizations>) at vector.tcc:293 293 std::_Destroy(this->_M_impl._M_start, this->_M_impl._M_finish, (gdb) 295 _M_deallocate(this->_M_impl._M_start, (gdb) std::_Vector_base<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_deallocate () at /usr/include/c++/4.2.1/bits/stl_vector.h:135 136 if (__p) (gdb) std::vector<std::pair<char const*, char const*>, std::allocator<std::pair<char const*, char const*> > >::_M_insert_aux (this=0x1001bfd40, __position={_M_current = 0x0}, __x=<value temporarily unavailable, due to optimizations>) at vector.tcc:298 298 this->_M_impl._M_start = __new_start; (gdb) 299 this->_M_impl._M_finish = __new_finish; (gdb) 300 this->_M_impl._M_end_of_storage = __new_start + __len; (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at vector.tcc:103 103 return iterator(this->_M_impl._M_start + __n); (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:183 183 p = demangler.insert(p, std::make_pair(mangled, demangled)); (gdb) 185 } (gdb) ~free_mem [inlined] () at /Users/bray/sources/boost_1_43_0/libs/python/src/converter/type_id.cpp:86 87 std::free(p); (gdb) boost::python::detail::gcc_demangle (mangled=0x7fff885a066c "c") at libs/python/src/converter/type_id.cpp:189 189 } (gdb) boost::python::converter::(anonymous namespace)::throw_no_lvalue_from_python (source=<value temporarily unavailable, due to optimizations>, converters=<value temporarily unavailable, due to optimizations>, ref_type=0x1001a8e55 "pointer") at libs/python/src/converter/from_python.cpp:215 215 )); (gdb) handle<PyObject> [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/handle.hpp:75 75 : m_p( (gdb) boost::python::detail::manage_ptr<_object> (p=0x1005ad6b8) at handle.hpp:55 55 inline T* manage_ptr(T* p, ...) (gdb) 57 return expect_non_null(p); (gdb) expect_non_null<PyObject> [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/errors.hpp:43 44 if (x == 0) (gdb) 0x000000010018a81d in boost::python::converter::(anonymous namespace)::throw_no_lvalue_from_python (source=<value temporarily unavailable, due to optimizations>, converters=<value temporarily unavailable, due to optimizations>, ref_type=0x1001a8e55 "pointer") at libs/python/src/converter/from_python.cpp:215 215 )); (gdb) boost::python::converter::(anonymous namespace)::throw_no_lvalue_from_python (source=<value temporarily unavailable, due to optimizations>, converters=<value temporarily unavailable, due to optimizations>, ref_type=0x1001a8e55 "pointer") at libs/python/src/converter/from_python.cpp:217 217 PyErr_SetObject(PyExc_TypeError, msg.get()); (gdb) 219 throw_error_already_set(); (gdb) boost::python::throw_error_already_set () at libs/python/src/errors.cpp:61 61 throw error_already_set(); (gdb) error_already_set [inlined] () at /Users/bray/sources/boost_1_43_0/boost/python/errors.hpp:19 19 virtual ~error_already_set(); (gdb) boost::python::throw_error_already_set () at libs/python/src/errors.cpp:61 61 throw error_already_set(); (gdb) TypeError: No registered converter was able to extract a C++ pointer to type char from this Python object of type str Program exited normally.

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Re: [Boost-users] [Boost.Thread - promise::lazy_init()] core dump when sharing promise between threads
by Thijs Terlouw 12 Aug '10

12 Aug '10

From: Anthony Williams <anthony.ajw(a)gmail.com> >It's a bug. Please raise a trac ticket. >Anthony Thanks, I have raised a trac ticket and also included a small test program that demonstrates the problem (as suggested by another user of the mailing list). https://svn.boost.org/trac/boost/ticket/4531 Thijs

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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; }

4 8

[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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