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[context] Why does boost::ctx::minimum_stacksize() on Windows return 65536
by Hartmut Kaiser 05 Sep '12

05 Sep '12

Hey all, Why is the minimally possible stack size in Boost.Context on Windows set to be 64k? This seems to be way too high for applications where only a minimal amount of stack is required. I assume, that since Boost.Context allocates the stack using VirtualAlloc the minimum possible value should be equal to the page size (see http://msdn.microsoft.com/en-us/library/windows/desktop/aa366887(v=vs.85).as px). Regards Hartmut --------------- http://boost-spirit.com http://stellar.cct.lsu.edu

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Mail moderated?
by Klaim - Joël Lamotte 05 Sep '12

05 Sep '12

Hi I sent an email to this list this morning that apparently got into moderation because it contained some text files with logs. I'm just not sure it's been noticed by moderators, as it might have been marked spam or something? Joel Lamotte

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Re: [boost] [Review.Coroutine] Some comments
by Oliver Kowalke 05 Sep '12

05 Sep '12

> * I don't know if showing the signature in the documentation will be > more informative. OK > * Could you add the following noexcept specifier? OK > * As the template class Allocator is not used to allocate internal > memory of the coroutine class. Could the Allocator parameter be renamed > StackAllocator? OK > * Could you add an standard Allocator parameter as e.g. the one of > packaged_task? > > C++ International Standard > > * I understand that the Boost.Context Allocator parameter is part od the > class, as context is a low-level class, but coroutine is more high > level. Is there a possibility to type erase the StackAllocator (and > preceding Allocator) template parameter, as packaged_task do? This will > allow to store coroutines (and generators) with the same signature in a > container even if they don't share the Allocator. You mean coroutine would have two allocators - one for allocating internal memory and one for allocating the stack? Removing the StackAllocator from the template arguments of coroutine should not that problem (would require an internal pointer to an internal interface - maybe detail::context_exec is a candidate). I've some concerns about having two allocator objects in coroutine's ctor . > * Parameters and move semantics. Could the signature parameters be > rvalue references? > > R operator()(A0 a0, ..., A9 a9); Hmmm - this would require a second version of opertor() and all arguments are moveable?! R operator()(BOOST_RV_REF( A0) a0, ..., BOOST_RV_REF( A)) a9); > I'm asking this because I think that Boost.Tuple has not implemented yet > move semantics. don't know - would that be an issue > * What about moving some of the coroutine/generator optional parameters > to a coro::attributes class > > std::size_t size = ctx::default_stacksize(), > flag_unwind_t do_unwind = stack_unwind, > bool preserve_fpu = true, instead of passing those threee params as args to coroutine ctor? good point > * Usually (at least in the C++ standard) a function doesn't throws > because of its preconditions are not satisfied. then assert? pre-conditions should be checked but how should I react if I get garbage from the user? > This should be coherent with > > > |Result operator()()| > > Preconditions: > > |*this| is not a /not-a-generator/, |! is_complete()|. > > which doesn't throws any specific exception if the preconditions are not > satisfied. does an assert - OK the I'll replace throwing excpetions be assertions > Documentation > ========= > > coroutine.html > > s/it can migrated between threads/it can migrate between threads/ OK > s/yield_return/yield_break/ > > * documentation for the following constructor is missing in the reference > > template< typename Fn > > coroutine( Fn && fn, > std::size_t size = ctx::default_stacksize(), > flag_unwind_t do_unwind = stack_unwind, > bool preserve_fpu = true, > Allocator alloc = Allocator() ); OK I think it will be easy to incorporate your suggestions - but during the boost.context review I was told not to modify the reviewd library (if the review is still on-going). regards, Oliver

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[rational] Over/underflow checked update ready for comments
by Dan Searles 05 Sep '12

05 Sep '12

>>> Quick overview of the update: the original usage and >>> code of the template class remains mostly as before, ie >>> boost::rational<int> RationalVar; should work as >>> in the original version. Adding 'true' as a second >>> template parameter, however, allows an exception to >>> be raised if an operation with a class variable results >>> in a value that can't accurately be represented >>I haven't looked at anything else, but I dislike using true/false as the template argument. I'd prefer meaningful names. _____ >>Rob Stewart robert.stewart(a)sig.com >>Software Engineer using std::disclaimer; >>Dev Tools & Components >>Susquehanna International Group, LLP http://www.sig.com >Replaced the bool template parameter with an enum: >enum RationalChecktype {RationalNoChecking, RationalCheckforOverflow}; For those interested in the rational number class, see: https://svn.boost.org/svn/boost/sandbox/rational Requesting comments on the code, and review for inclusion in the next release. Dan Searles

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very simple implementation of Andrei Alexandrescu's ScopeGuard idiom
by Sergey Radionov 04 Sep '12

04 Sep '12

https://github.com/RSATom/finally_execute/blob/master/finally_execute.h based on http://www.drdobbs.com/cpp/generic-change-the-way-you-write-excepti/1844037… I know about http://sourceforge.net/projects/loki-lib/ but with boost::bind this can be much simpler: https://github.com/RSATom/finally_execute/blob/master/README I've used this in many of my projects, and found it very usefull.... don't understand, why this simple solution does not contributed already to Boost by someone else... :)

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[graph] property_value no longer valid for bgl_named_parameters
by Alex Hagen-Zanker 04 Sep '12

04 Sep '12

The transition from Boost 1.49 to 1.51 gave me a breaking change in the graph library: Originally I used the property_value struct to get the type of a named parameter, like this: property_value<bgl_params, Tag>::type; This no longer works and the current use seems to be: get_param_type<Tag, bgl_params>::type; Is this a regression? Or was I just using the library in the wrong way? Thanks, Alex

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Enum Conversion
by Roland Bock 04 Sep '12

04 Sep '12

Hi, In a lot of projects in the company I work for we use Ice middleware which allows to define nice interfaces for services. The IDL also allows to define enums, but I cannot set specific values for the enum items. We also need to store some of these values in databases. We use int to represent the enumerations. Since we might feel the need to add more items to an enum or delete an unused one, we cannot just cast enum to int and vice versa when writing to or reading from the database. We need methods that translate enum to int and back in a stable way that won't change for an individual enum item, even if its position in the enum changes. I found a way to do this, which provides enum<->int and enum<->string. It is used like this: typedef enum { Alpha, Beta, Gamma, Delta, Epsilon } Greek; CREATE_CONVERTER_METHODS(Greek, (Alpha, 5), (Beta, 3), (Gamma, 7), (Delta, 1), (Epsilon, 6)); std::cout << GreekToString(IntToGreek(1)) << std::endl; std::cout << GreekToString(IntToGreek(6)) << std::endl; std::cout << GreekToInt(Alpha) << std::endl; std::cout << GreekToString(Alpha) << std::endl; std::cout << IntToGreek(17) << std::endl; ------ $ ./a.out Delta Epsilon 5 Alpha terminate called after throwing an instance of 'std::invalid_argument' what(): unexpected Greek value My questions are: a) Is this something that might be interesting for others as well? (Or does boost even offer something like that already?) b) I'd really like to be able to write this instead: CREATE_CONVERTER_METHODS(Greek, Alpha = 5, Beta = 3, Gamma = 7, Delta = 1, Epsilon = 6); Obviously, if I could use the preprocessor to translate Alpha = 5 -> (Alpha, 5) I'd be done. But I have no idea how to do that. Any suggestions? Thanks and regards, Roland

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[Contract] noexcept and custom contract violation handlers
by Andrzej Krzemienski 04 Sep '12

04 Sep '12

Hi, I have just realized that there is an interesting interaction between "noexcept" and Contract Programming framework. Not only Lorenzo's library, but even if contracts were a language feature. N3248 ("noexcept prevents library validation", http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3248.pdf) recommends that functions with any preconditions should not be declared noexcept(true) in case someone wants to report precondition failures via exceptions. If preconditions become part of declaration syntax, declaring both precondition and noexcept(true) could (and should?) be recognized as compile-time error. But now also invariants and postconditions come into play: if a function declares a postcondition, or our class defines an invariant, should we be allowed to declare our function noexcept? What if someone wants to report an invariant or postcondition failure via special exception? (I do not have a good answer for it.) Regards, &rzej

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[contract] invariant checking after destructor throw
by Andrzej Krzemienski 04 Sep '12

04 Sep '12

I have found a potential issue while reading the documentation. (The documentation is very good BTW). It says that the non-static invariant is still checked if object's destructor throws an exception. Am I reading it right? If so, I believe this is not correct. I have two problems with it: 1. According to the standard, an object is considered destroyed (its life-time has ended) when its destructor *starts*. Even if it throws an exception, it is considered destroyed, so accessing its members (in order to check for the invariant) may be illegal (an undefined behavior). 2. Why such an object (that threw on destruction) would need to preserve the invariant? You cannot access it or use it or even destroy it the second time, because it has already been destroyed. No-one will notice it anyway. Or am I missing something? Regards, &rzej

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[Review:Contract] Late review
by Steven Watanabe 03 Sep '12

03 Sep '12

AMDG First of all, *Yes, Contract should be accepted into Boost* I've only really looked at part of the documentation so far. Here's my comments from that. I may have more later depending on how much time I have. index.html: - "Contract Programming (CP) allows to specify" Use a gerund (specifying) instead of an infinitive. An infinitive here needs a subject. - "... allowing to find bugs ..." Same problem, although it can't be fixed in the same way, since the participle + gerund would sound awkward. It could be handled with a passive infinitive. (allowing bugs to be found) - "and it was first introduced by the Eiffel programming language " You can leave out the "it." It sounds awkward to me. - "Eiffel programming language" Using this repeatedly sounds a bit pedantic. You can just say "Eiffel" after the first occurance. - The side by side code in the example gets a bit wide. This will definitely be a problem if you want the documentation to be generated as a PDF. - I don't understand why the library needs to deal with access control. Why can't the user just use public: private: protected: as usual? - CONTRACT_OLDOF kind of sticks out at me. I don't really like the way it looks having it a macro when everything else is keywords that are parsed by the top level macros. - "...if there is a bug in the function caller for which push_back is called when size is equal to max_size ..." This clause is somewhat confusing. - "...with the assertion number to uniquely identity..." s/identity/identify/. Also don't split infinitives. - "This library suffers of two limitations" s/of/from/ getting_started.html: - "This section explains how to setup..." "set up" should be two words. "setup" as one word is a noun. - "... failure of the checked condition does not abort the program, instead ..." Run on sentence. - "The implementation of this library uses..., templates with partial specializations and function pointers (similarly to Boost.Function), ..." I don't understand the connection between partial specialization and function pointers. Why are they grouped together? contract_programming_overview.html: - "It is assumed that programmes" s/programmes/programmers/ - "...to formally program specifications". Don't split the infinitive. "to program specifications formally" - "Then, this library aims to be ..." "Then" doesn't sound right here. "Then" is usually used for conditions ("if... then") or sequences (e.g. First.... Then...), but there's nothing for it to connect to here. - "Contract Programming is characterized by the following type of assertion mechanisms." s/type/types/ - "before the body execution." I think it would sound better to use the possesive "body's execution" or "execution of the body". rather than apposition. - "Preconditions cannot be strengthen, postconditions and class invariants cannot be weaken. " s/strengthen/strengthened/, s/weaken/weakened/ - I'm not sure that I would consider Subcontracting to be an assertion mechanism. - "Block Invariants | These are logical conditions that programmers except ..." s/except/expect/ - "...while a contract assertions is ..." s/assertions/assertion/ - "This library implement this feature however it should be noted ..." Run on sentence. - "protect such a global variable from racing conditions " It's called a "race condition." - "but that will effectively introduce a global lock in the program" This seems like a classic use case for thread specific storage. - "Furhtermore," s/Furhtermore/Furthermore/ - "Contracts are part of the source code, they are..." Run on sentence (comma splice) - "detailed error messages that greatly helps debugging" "helps" needs to agree with "messages." - "Contract Programming benefits come to the cost of performance " "to" is the wrong preposition. Try "at." - "The run-time performances are negatively ..." "performance" should be singular. Plural doesn't really make sense for abstract nouns like this. - "1. The extra processing required to check the assertions. 2. The extra processing required by the additional function calls (additional functions are invoked to check preconditions, postconditions, class invariants, etc)." How is (2) different from (1)? - "checking function arguments using postconditions " I think you mean /pre/conditions. - "so that these initializations can relay" s/relay/rely/ - "C++ object construction mechanism ..." You need an article. "The C++..." - "Check the non-static class invariants, but only if the body threw an exception." This could use a rationale. Destructors are generally not supposed to throw at all. - "Contracts are only responsible to check the " "for checking" instead of "to check." - "...to only use public members, Eiffel instead ..." Split infinitive, run-on sentence. - "...are allowed to brake class invariants..." s/brake/break/ - "Arbitrary code in contracts | No, assertions only." This is a bit misleading, since assertions can execute arbitrary code. tutorial.html: - "complete guide on this library syntax" s/library/library's/ - result == oldof valule s/valule/value/ - "int const" IIRC, you can't have a const rvalue of a built-in type. - "parameter names can instead by omitted " s/by/be/ - params_postinc You didn't update the pre/post conditions when you copied this from the last example. - "Function and array types cannot be directly used as function parameter types within the contract macros but extra typedef declarations can be used to workaround this limitation " This workaround doesn't work in function templates where the array element or dimension is deduced. - "the maximum number of supported array dimensions is specified by the CONTRACT_CONFIG_ARRAY_DIMENSION_MAX macro" I don't understand the reason for this limitation. - "...evaluates all contract conditions in constant-correct context" Add an article "a" before "const-correct." - "the type of value type" Delete the second "type." - ConstantCopyConstructible You're definitition of CopyConstructible is wrong. A type that only defines T(T&) is not CopyConstructible. - "However, it is still necessary to ontract" s/ontract/contract/ - unique_identifiers I think it's worth pointing out that the postcondition can't assume that the precondition was true in the face of subcontracting. I did a double take when I saw old_found. - "Wakened inherited preconditions ..." s/Wakened/Weakened/ oldof.hpp: The definition of CONCEPT_OLDOF is a bit dangerous. It can't safely be passed as a macro argument. What do you think of this bit of PP magic: #define TEST_EXPAND_EXPAND_OLDOF(x) CONTRACT_OLDOF #define TEST_EXPAND_NOTHING(x) oldof #define TEST_EXPAND_I(x) TEST_EXPAND_ ## x #define TEST_EXPAND(x) TEST_EXPAND_I(x) #define oldof TEST_EXPAND(EXPAND_OLDOF(NOTHING(z))) #define EXPAND_OLDOF(expr) expr oldof -> expands to itself EXPAND_OLDOF(random text oldof more random text) -> expands to random text CONTRACT_OLDOF more random text General: - Are ellipsis parameters allowed? - Just say "parentheses," not "round parentheses." Parentheses without any qualification always means (). In Christ, Steven Watanabe

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