August 2009 - Boost - lists.boost.org

[Interprocess] Possible bug in shared memory on FreeBSD 8.0
by Manish Vachharajani 11 Aug '09

11 Aug '09

I've been happily using Boost.Interprocess to create shared memory regions under FreeBSD 7.2, however, I am having issues on FreeBSD 8.0 pre-release. I can reproduce the problem with Boost 1.39.0 and the svn trunk. The source of the problem appears to be that Boost.Interprocess calls lseek on a file descriptor returned by shm_open, but the results of such an lseek are undefined. Below, I explain further how I came to this conclusion. If you run the program I've appended to the end of this email, the constructor for managed_shared_memory throws an interprocess_exception with error code 29 which is Illegal Seek on FreeBSD. A little bit of system call tracing and debugging reveals that the offending seek is in mapped_region.h:447 (in svn revision 55512). However, digging around, it appears that lseek's behavior on file descriptors for shared memory regions is undefined (See http://www.opengroup.org/onlinepubs/000095399/functions/lseek.html for what IEEE 1003.1 standard has to say about this.) I've confirmed that FreeBSD 7.2 allowed such seeks but 8.0 does not by looking at the kernel source code. For what it's worth AIX 6.1 does not allow such seeks either (see http://publib.boulder.ibm.com/infocenter/systems/index.jsp?topic=/com.ibm.a…) Could someone advise me on what the correct fix for this bug is? I'd be glad to implement it, but I'm not sure what the right fix ought to be. #include <iostream> #include <string> #include <exception> #include <boost/interprocess/managed_shared_memory.hpp> namespace bip = boost::interprocess; int main(const int argc, const char *argv[]) { bool error = true; std::string shmName("testShmRegion"); bip::shared_memory_object::remove(shmName.c_str()); try { std::auto_ptr<bip::managed_shared_memory> segment(new bip::managed_shared_memory(bip::create_only, shmName.c_str(), 12345)); error = false; } catch(const std::exception &e) { std::cerr << "Error: " << e.what() << std::endl; } if(!error) { std::cout << "Shm allocated successfully." << std::endl; } return 0; } Manish

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[asio] very confusing title
by DE 11 Aug '09

11 Aug '09

when i personally see 'asio' i immediately think about steinberg technology asio which stands for 'audio stream i/o' so it's up to you of course just want you to know

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Vault access for Boost.Debug
by Zachary Turner 11 Aug '09

11 Aug '09

Hello, I'd like to request access to the vault. I'm going to upload a proof-of-concept of some of the things I mentioned earlier in my thread about Boost.Debug. This early version gives simple stack traces in limited scenarios, only supports Windows, and isn't designed very well. Here's an example of a program using it in its current form: void test_func(int argc, int argc2, char* argv[]) { stack_trace trace(10); //Maximum depth of 10 levels std::cout << trace.string() << std::endl; } int main(int argc, char* argv[]) { test_func(argc, argc, argv); return 0; } and an example of the stack trace printed as a result of this program: void test_func(int, int, char**) [f:/dev/stack_trace/main.cpp:10] int main(int, char**) [f:/dev/stack_trace/main.cpp:23] int __tmainCRTStartup() [f:/dd/vctools/crt_bld/self_x86/crt/src/crtexe.c:406] int mainCRTStartup() [f:/dd/vctools/crt_bld/self_x86/crt/src/crtexe.c:389] It also currently supports printing the names of all the arguments, but it was hackish and I left it out until it undergoes some redesign. There is currently no documentation, but as this is just a proof of concept I'm currently only looking for people to help out with actual code and/or provide input, so I think that's ok for now. Thanks

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enum / string translation
by Zachary Turner 11 Aug '09

11 Aug '09

I wrote some code to perform both compile-time and runtime translation between enums and their corresponding string values. The only direction that isn't possible is string->enum at compile time. Is there any interest in this? You can use it as follows: typedef enum { ValueA1, ValueA2 } EnumA; typedef enum { ValueB1, ValueB2 } EnumB; BEGIN_ENUM_MAP_DECLS() BEGIN_ENUM_MAP(EnumA, a_map) ENUM_MAP(ValueA1) //maps ValueA1 to the string "ValueA1", provides both compile-time and run-time lookups. ENUM_MAP_NAME(ValueA2, "custom name") //maps ValueA2 to the string "custom name", provides both compile-time and run-time lookups END_ENUM_MAP() BEGIN_ENUM_MAP(EnumB, b_map) ENUM_MAP(ValueB1) ENUM_MAP(ValueB2) END_ENUM_MAP() END_ENUM_MAP_DECLS() void foo() { //value -> string, compile time BOOST_STATIC_ASSERT(enum_map<EnumA>::value_lookup[ValueA2] == "custom name"); //value -> string, runtime EnumB some_value = get_enum_b_from_external_source(); std::cout << "some_value = " << enum_map<EnumB>::name_lookup[some_value] << std::endl; //prints either 'some_value = ValueB1', or 'some_value = ValueB2' //string -> value, runtime EnumA value = enum_map<EnumA>::name_lookup["custom name"]; BOOST_ASSERT(value == ValueA2); } One particularly useful application of this that I've found is with regards to boost::program_options. You can provide an overload of boost::program_options::validate that uses boost::enable_if with boost::is_enum thus providing automatic support for entry of friendly names corresponding to enumerations on the command line or in a config file. Obviously there's many other easily identifiable uses as well. However, this is a common enough problem that I wonder if anyone else has already attempted something like this, and if so maybe I can look at their code first, or just scrap mine altogether and reuse something existing. If not, I'm sure there is plenty of room for improvement in mine but if it could fit somewhere in boost (perhaps boost/utility) I'd be willing to submit it and make necessary improvements. Unfortunately I don't think it's technically possible to have a simple syntax, even through preprocessor magic, that requires you to only specify the name of each enumerated value once, and end up providing both a definition of the enumeration as well as the mapping from string<->value, but if someone comes up with a way that would obviously be ideal.

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[move] moving temporaries of copyable types
by klaus triendl 10 Aug '09

10 Aug '09

Hi, I've recently taken a look at the Boost.Move library and it seems that it is only possible to make 1) either non-copyable types movable or 2) make copyable types move-aware by explicitly moving them. Now, I've discovered for myself that it is possible for pre-c++09 compilers to make copyable types *implicitly* movable by detecting temporaries that can be moved. So, my question is whether this is well-known and this feature was deliberately excluded from Boost.Move or nobody has discovered it yet. It would be great to have support for copy- and (implicit) move-semantics. Klaus Triendl

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[type_traits] is_less_comparable
by Frédéric Bron 10 Aug '09

10 Aug '09

Hi, One year ago, I added to the sandbox the following type_traits: - is_equal_to_comparable, - is_greater_comparable, - is_greater_equal_comparable, - is_less_comparable, - is_less_equal_comparable, - is_not_equal_to_comparable They allow to check if type T can be compared, i.e. if operator==, >, >=, <, <=, !=(T&, T&) exist. At that time, I could not build the documentation so the addition has never been reviewed. I have now a larger hard disk which allows me to have a virtual machine running linux (ubuntu). I would like to check if my documentation addition is OK, therefore could you tell me how I can compile .qbk files? Then, I would like to submit the addition for a review and future inclusion in a boost release; what is the procedure? Regards, Frédéric

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[proto]: rewriting POOMA and Blitz++
by Chandrashekhar Kumar 10 Aug '09

10 Aug '09

Hello, At some time Eric expressed that all the expression template based libraries of boost (notably Phoenix, Spirit) has to be re-written using proto. I think that this target is kind of achieved by now. Can something be done along the similar lines for re-writing the top-notch libraries like POOMA and Blitz++ as a complete examples of proto applications? Does anyone has idea about how huge this undertaking can be? Thanks, Chandra

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"I want everything" should build "out of the box" (on Windows)
by KTC 09 Aug '09

09 Aug '09

Users on Microsoft Windows should be able to build boost with everything, both in terms of all supported variants and all boost libraries, with a single command to bjam assuming they have all the optional supporting libraries available. An user download boost, and want to build all the libraries that require building go read the Getting Started Guide <.../getting_started/windows.html#invoke-bjam> and see the after getting bjam they use the command bjam --build-dir=build-directory toolset=toolset-name --build-type=complete stage So they enter that into the command prompt and see lots of warnings and notes about missing optional components. The warnings and notes itself is fine and informative. Actually, it's incomplete as it stand as it doesn't tell the user about Boost.IOStreams optional component requirement of bzip2 & zlib headers. Okay, the user go and install all the optional components the warnings and notes tell them. After installing Python, ICU (building it first), Expat (building it first), and MPI (say MS-MPI), they try again. This time with the command becoming bjam --toolset=... --build-dir=... --build-type=complete -sHAVE_ICU=1 -sICU_PATH="..." -sEXPAT_INCLUDE="..." -sEXPAT_LIBPATH="..." -sBZIP2_SOURCE="..." -sZLIB_SOURCE="..." stage Nope, MPI requires modification of user-config.jam or building it on its own with --with-mpi. Why? No other optional components build that way. So they look to see how they do that, and does it. Second attempt and ... nope. New to 1.39 is the errors error: link=shared together with runtime-link=static is not allowed error: such property combination is either impossible error: or too dangerious to be of any use due to the changes made as a result of <http://lists.boost.org/Archives/boost/2009/04/150675.php>. (Recently noted on <http://groups.google.com/group/boost-list/browse_thread/thread/2a7bd07468b5…>.) While catching those errors is good, maybe it should be fixed as well such that it doesn't come up in the first place if someone do a --build-type=complete with ICU. So now the users have to build Boost.Regex separately from the rest of the library (after finding how to pass the link= & runtime-link= options). By the way, at this point I would like to point out how it's strange that -sHAVE_ICU=1 mean to build with ICU, but so is -sHAVE_ICU=0 .... :S And ... nope, even separately Boost.Regex still wouldn't build without errors. No one told them they need to rename icuin.lib, icuind.lib, icuind.pdb & icudt.lib from ICU to icui18n.lib, icui18nd.lib, icui18nd.pdb & icudata.lib respectively. With Boost.Regex built, we turn to the rest of the library with --without-regex. After waiting a while, we discover ... nope, Most of the library is built but not Boost.Graph. Sorry, this time no one told them they need to change Boost.Graph's Jamfile.v2 file with "<find-shared-library>expat" to "<find-shared-library>libexpatwMT" and adding "<define>XML_STATIC". Boost is great, it's free, it's flexible and I understand it's developed for free by volunteers, but its "installation" for someone that want every libraries could be improved. :-) Regards, KTC -- Only two things are infinite, the Universe and Stupidity. And I'm not quite sure about the former. - Albert Einstein

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[Interprocess::Semaphore] Deadlock on more producers - one consumer problem
by Cosimo Calabrese 09 Aug '09

09 Aug '09

Hi to all, I've a buffer of 10 positions; 4 producers put elements on the buffer and only 1 consumer pick them; the producers generate elements very fastly, but the consumer picks the element very slowly. I've decided to synchronize the producers and the consumer with a boost::interprocess semaphore initialized to 10. Before to put an element in the buffer, the producer execute a wait() in the semaphore; the 4 producers put quickly 10 elements in the buffer, so they all block on the wait(). When the consumer picks an element from the buffer, it performs a post() on the semaphore. Here is the problem: the post() unlocks only one of the 4 producers. Consider this scenario: - the producers are all in wait state; the semaphore counter is 0; - the consumer picks an element and perform a post(), that unlocked the producer_1; the semaphore counter is 1; - the producer_1 is unlocked but it doesn't produce any element; the other producers are locked; - the consumer picks the other 9 elements in the buffer and perform the 9 post() on the semaphore, but the semaphore counter becomes 2, 3, 4, ... 10, and so the semaphore doesn't signal the other producers, that remains in lock state(). --> DEADLOCK. Is there a way to unlock all the producers with the boost::interprocess::semaphore? Or I have mistaken the approach of the problem? Thanks to all, Cosimo Calabrese.

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backward binary compatibility of boost shared libraries
by Андрей Пономаренко 08 Aug '09

08 Aug '09

Hello, I'm from Institute for System Programming of Russian Academy of Sciences and we are developing a free lightweight tool for checking backward/forward binary compatibility of shared C/C++ libraries in OS Linux. It checks interface signatures and data type definitions in two library versions (headers and shared objects) and searches ABI changes that may lead to incompatibility. We have released 1.2 version of this tool and we'd like you to consider its usefulness for your project. The wiki-page with the latest release of binary compatibility checker is http://ispras.linux-foundation.org/index.php/ABI_compliance_checker Andrey Ponomarenko

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