May 2008 - Boost - lists.preview.boost.org

[futures] reference-counted futures
by Frank Mori Hess 28 May '08

28 May '08

It's occurred to me that support for reference counting futures (which Peter Dimov has suggested a couple times) could be added simply by adding a method to the promise class bool promise::has_future() const; The has_future query would not alter the state of the promise (it wouldn't put it into some unusable "expired" state). It would simply allow the promise-setting thread to query if there are any futures and take whatever action it chooses. So it wouldn't put any burden on someone who wants to code a fire-and-forget function that returns a future that may be safely discarded. In a typical implementation, has_future might boil down to a call of shared_ptr::unique(). This works because threads don't block waiting on promises, only on futures. When a future's promise is destroyed without ever being fulfilled, action has to be taken to give the waiting futures an exception to prevent a thread from blocking forever in vain. But if a promise's last future disappears, it doesn't need to take any action. All it needs to do is provide a query that can be used by interested code to detect that fact. Also, for debugging a unsigned promise::future_count() const; method could be provided, which might be implemented by returning the value of shared_ptr::use_count minus one. Any thoughts? These functions could be added independently of whether or not an explicit future::cancel() is supported.

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Spirit 2 and backwards compatibity?
by John Maddock 28 May '08

28 May '08

I'm having trouble building an app that uses spirit from SVN Head with gcc-4.2 (Mingw32), I see: In file included from c:\data\boost\boost\trunk/boost/spirit/home/classic/core/p arser.hpp:14, from c:\data\boost\boost\trunk/boost/spirit/home/classic/core.h pp:29, from c:\data\boost\boost\trunk/boost/spirit/include/classic_cor e.hpp:11, from c:\data\boost\boost\trunk/boost/spirit/core.hpp:21, from main.cpp:17: c:\data\boost\boost\trunk/boost/spirit/home/classic/core/scanner/scanner.hpp: In member function 'typename boost::detail::iterator_traits<IteratorT>::value_type boost::spirit::scanner<IteratorT, PoliciesT>::operator*() const': c:\data\boost\boost\trunk/boost/spirit/home/classic/core/scanner/scanner.hpp:259 : error: 'iteration_policy_t' has not been declared Any ideas? Note that simply including spirit/core.hpp is enough to trigger this error. Thanks, John.

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Platform Champions needed
by Beman Dawes 28 May '08

28 May '08

Awhile back, there was discussion of setting up a list of platform champions. Platform champions are experts that Boost developers can turn to when they have a problem with a particular compiler or operating system. Whether it is a question about configurations, features, or submitting a bug report to the compiler supplier, these folks know the ropes for the platform. If you are knowledgeable about at platform, and would like to be a platform champion, please add yourself to the list! The list is found at http://svn.boost.org/trac/boost/wiki/PlatformChampions --Beman

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thread_group
by David Abrahams 28 May '08

28 May '08

I don't know if thread_group is supposed to stay around now that we have movable threads, but if we're going to keep it I would like to propose a few changes. 1. add_thread should take an auto_ptr<thread> (and eventually unique_ptr<thread>) so the signature indicates the ownership transfer. 2. remove_thread should be called release_thread. "Release" is at least not ambiguous about whether the thing is being destroyed. -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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iterator_facade, decoupling of access and traversal?
by Roland Schwarz 28 May '08

28 May '08

After having read http://www.boost.org/doc/libs/1_35_0/libs/iterator/doc/index.html I have been left, believing that the new iterator concepts will allow me to create an iterator that may return a proxy instead of a reference. I tried to do this by using the iterator_facade template, and for the "Reference" parameter I specified a proxy class that has a conversion operator to the "Value" type. This almost works, but fails for expressions of Val v = it[n]; expressions, because iterator facade does not return "Reference" objects in that case, but operator_brackets_proxy objects that are convertible to "Reference". So I am wondering if I understand something wrong? Isn't the decoupling of access and traversal meant to allow "Reference" be a proxy object? Any hints appreciated! -- _________________________________________ _ _ | Roland Schwarz |_)(_ | aka. speedsnail | \__) | mailto:roland.schwarz@chello.at ________| http://www.blackspace.at

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movable threads, locks, and boost::array
by David Abrahams 27 May '08

27 May '08

I just discovered that while none of my standard containers are "move-aware" in the way needed by boost::thread, I can use boost::array to store threads by simply move-assigning new threads into the elements it contains: boost::array<boost::thread, 100> thread_q; for (int i = 0; i < 100; ++i) thread_q[i] = boost::thread( some_function ); it ain't perfect, but given that the number of cores on any real machine is limited these days, you can do a lot with a fixed-size array of thread. Pretty cool; it sure beats using shared_ptr. -- Dave Abrahams BoostPro Computing http://www.boostpro.com

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[exception] enable_error_info.hpp compile errors
by Beman Dawes 27 May '08

27 May '08

Boost.Filesystem's wide_test is failing on trunk due to enable_error_info.hpp compile errors. It's happening with many (or maybe all) compilers. See below for typical error messages. --Beman ..\boost/exception/enable_error_info.hpp(23): error: not a class or struct name public T, ^ detected during: instantiation of class "boost::exception_detail::error_info_injector<T> [with T=char [29]]" at line 90 instantiation of "boost::exception_detail::enable_error_info_return_type<T>::type boost::enable_error_info(const T &) [with T=char [29]]" at line 58 of "..\boost/throw_exception.hpp" instantiation of "void boost::throw_exception(const E &) [with E=char [29]]" at line 114 of "..\libs\filesystem\test\wide_test.cpp" ..\boost/exception/enable_error_info.hpp(28): error: "T" is not a nonstatic data member or base class of class "boost::exception_detail::error_info_injector<char [29]>" T(x) ^ detected during: instantiation of "boost::exception_detail::error_info_injector<T>::error_info_injector(const T &) [with T=char [29]]" at line 95 instantiation of "boost::exception_detail::enable_error_info_return_type<T>::type boost::enable_error_info(const T &) [with T=char [29]]" at line 58 of "..\boost/throw_exception.hpp" instantiation of "void boost::throw_exception(const E &) [with E=char [29]]" at line 114 of "..\libs\filesystem\test\wide_test.cpp"

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Re: [boost] Question regarding logging, persistence, threadcommunication, network messaging and async frameworks
by brass goowy 27 May '08

27 May '08

Scott Woods writes: >Hi, >Is there a place in Boost for a library that tackles all of the above? I >believe the realistic >answer is no but I would be happy to be proven wrong. >Work in the different areas mentioned in the subject line recently collapsed >into a single >underlying technique. Given the example UDT below; >struct person >{ >std::string name; >std::vector<unsigned> score; >std::set<string> team; >}; >persistence is achieved using; >person new_member; >codec_object<person> configuration( "profile" ) >configuration << new_member; // Save in a disk file name >"profile" >configuration >> new_member; // Load from the same disk file >transmitting the same object between threads looks like; >send( new_member, other_thread ); >while receiving that transmission occurs in code that looks like; >my_thread::received( person &new_member ) >{ >.. >} >Transmission of messages across networks looks like; >send( new_member, socket_proxy ); >Yes, its the same as for inter-thread communications. The "socket_proxy" >just >happens to be a variation on "my_thread" that forwards materials it receives >onto a socket connection. >Logging looks like; >WINSOCK( socket, AF_INET << SOCK_STREAM << 0 ); >COMMENTARY( "connection to " << address_entered << " failed (" << >failure << ")" ); >Logging messages can be routed anywhere based on the type and unique >identity of >the originating party. >The fragments of code provided above hide a lot. While that's technically >desirable >I can appreciate that it might not flesh out my question at all (i.e. >...room in Boost). But >actually this is precisely the most compelling thing about the library - it >reduces code >that traditionally can be quite difficult into fragments such as those >shown. Shalom From what you've shown it looks like the duplication of data members in serialization methods is not needed. Some have been struggling to eliminate the need for that duplication -- http://preview.tinyurl.com/6kpx8t . Maybe more details about codec_object<> would be helpful. Brian Wood Ebenezer Enterprises www.webEbenezer.net

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promote "unwrap" to ref.hpp
by Ronald Garcia 27 May '08

27 May '08

Hi all, boost::reference_wrapper exists at the top-level of boost (in boost/ ref.hpp), but that header provides no way to unwrap a reference_wrapper. There are two implementations floating around of "unwrap", one in boost.bind's implementation details, and one in boost.mpl's implementation details. Is there any problem with providing a version of unwrap in ref.hpp? ron

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[test] Documentation confusion
by Maik Beckmann 27 May '08

27 May '08

Hello, I am confused about the boost.test documentation. There are docs in trunk and after some hours of digging via gmane if found this one http://www.patmedia.net/~rogeeff/html/index.html index.html in trunk : ... Revised: 28 February, 2006 index.html external link: Copyright © 2001-2007 Gennadiy Rozental ... My impression is that the 2007 version is much more comprehensive. Why isn't the most recent one in trunk? Do the trunk docs got a link the the external docs? -- Maik

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