September 2013 - Boost - lists.boost.org

proposal for metafunction mpl::eval
by klaus triendl 12 Sep '13

12 Sep '13

Hi, I'm not so much into meta-programming, so I'm not sure whether there's already an alternative available. Nevertheless I'd like to propose a new metafunction that simply evaluates its argument: template<typename F> struct eval: F::type {}; I've found it somehow useful because it avoids syntactical sugar when specifying a condition to be evaluated for eval_if: eval_if< eval<apply<UnaryF, Arg>>, F1, F2 >; instead of writing: eval_if< typename apply<UnaryF, Arg>::type, F1, F2 >; Any comments on this? -- klaus triendl

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[interprocess] Different processes accessing shared memory in different locations
by Tom Sanham 11 Sep '13

11 Sep '13

Hi Our application has the following scenario using Boost V1.0.52: 1) Process A writes to boost interprocess shared memory. The files appear at C:\ProgramData\boost_interprocess\... 2) Process A launches Process B 3) Process B attempts to read from shared memory but fails. It is attempting to read from: C:\Users\<username>\AppData\Local\Temp\boost_interprocess\... This failure only occurs on one single Windows 8 64 bit machine out of many we have tested. On all other machines, the application works perfectly. Please could somebody advise: What changes to our application could be made to avoid this? What changes to the machine's configuration (eg. Registry) could be made to avoid this issue? Many thanks Thomas Sanham

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[asio] Mixing streambuf-based async_read and async_read_until
by Gavin Lambert 11 Sep '13

11 Sep '13

I was tracing through some code today (using Boost.Asio 1.53) and noticed something that seems a little odd to me. Given a boost::asio::streambuf that already contains data (typically from a previous read), the async_read_until operation will check the buffer first to see if it can find the specified delimiter already, and will only fetch more data from the stream if it needs to. It does appear to perform at least one async_read_some per async_read_until call, but this will be a zero-length-read that will not actually hit the network/wherever. (Could probably be optimised a little further though.) The async_read operation however will not check the buffer. While it won't destroy any existing data (it just appends) it will still fetch additional data from the stream up to the specified completion condition, ignoring however much is already in the buffer. For example, if buf already contains 32 unconsumed bytes then async_read(s, buf, transfer_exactly(16), cb) will fetch 16 more bytes from the network, leaving 48 bytes in the buffer but only passing 16 to the read handler. Of particular note is that it will wait for those 16 bytes to be read from the network -- it's not satisfied with the data it already has. The net effect of these behaviours I think is that if you're using async_read_until exclusively or async_read exclusively then everything will behave fairly normally. If you are mixing these two operations on the same stream then you will either be losing data (if you use separate streambufs) or reading more data than you should (if you use the same streambuf and don't check outside of ASIO to see if it already contained enough data). Maybe it's just me, but I find it surprising that async_read doesn't check if the supplied streambuf already satisfies the completion condition, given that async_read_until does and the docs for async_read do say that it's allowed to make zero async_read_some calls. Is this a bug or is it expected behaviour?

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Incompatible Boost license file in boost.container
by Philip Bennefall 11 Sep '13

11 Sep '13

Hi all, I was looking at boost.container, and found that boost/container/deque.hpp has similar problems as boost/detail/endian.hpp had before that was fixed. Parts of deque.hpp seem to be covered by a license that is not compatible with the Boost software license. I quote: // Copyright (c) 1996,1997 // Silicon Graphics Computer Systems, Inc. // // Permission to use, copy, modify, distribute and sell this software // and its documentation for any purpose is hereby granted without fee, // provided that the above copyright notice appear in all copies and // that both that copyright notice and this permission notice appear // in supporting documentation. Etc. Kind regards, Philip Bennefall

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Re: [boost] [cpo-proposal] presentation of the idea
by Santiago Tapia 10 Sep '13

10 Sep '13

Hi, I have working in the implementation of the cpo library, so I keep working and I expect to make a formal proposal within 2 or 3 months, and meanwhile I will try my best to answer mails. > Date: Wed, 28 Aug 2013 11:18:03 +0400 > From: Andrey Semashev <andrey.semashev(a)gmail.com> > The storage strategy does not mandate the interface of the container. > unordered_set/map are implemented as a number of buckets (i.e. > single-linked lists), yet they provide sequence interface with an > additional ability to iterate within a single bucket. I don't see why a > similar approach couldn't be taken in your container. I will not provide the classifier container with a push_back or push_front method, instead I will use insert, I suppose it is just about the meaning of sequence, I expect a sequence to keep an order on items while container means just a collection of items in not a particular order. On the other hand I will provide a way to iterate over a "single bucket". Actually, I have been working on benchmarking and that seems to be the better option to iterate over the classifier because it reduces the number of virtual method calls in the iteration. I also will provide a const random access iterator and some other utilities to access a particular item in the container. > > You can't create std::multiset<shape> but you can create > boost::intrusive::multiset<shape>. The reason for that is that > std::multiset attempts to allocate storage for shape, while > boost::intrusive::multiset doesn't, leaving this to the user. This allows > you to insert any objects derived from shape to the single > boost::intrusive::multiset and work with this container pretty much the > same way you would with std::multiset. You can even insert the very same > object in multiple containers if you need to. I recommend you to have a > look at Boost.Intrusive, it is a truly amazing library. The interface for my library needs to be far more simple than the interface in Boost.Intrusive, but I will consider that option to implement the details. Up to now, I am only using std containers to avoid dependencies, but I will consider other options to optimize speed and size performance. [snip] About "polymorphic vector", that is, a container that stores different types contigously, I should say that the interface needs to be as easy as in the classifier, so I will discard solutions that needs any requirement to objects apart from being copyable, default constructive or the like. I will try to develop a prototype from Larry Evans' example (with his permission). But because I am not an expert on alignment and memory optimization, I will try to use something "more standard", actually I am going trying to use the allocator to compute the "right" address to place an object of a given type that is greater that a "free" memory pointer. In that way, I also expect to take advantages of allocator such as tbb cache aligned allocator. Again, thank you all for your comments. Regards, Santiago -- ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES UNIVERSIDAD POLITÉCNICA DE MADRID Santiago Tapia Fernández | DEPARTAMENTO DE AUTOMÁTICA, INGENIERÍA ELECTRÓNICA E INFORMÁTICA INDUSTRIAL José Gutiérrez Abascal, 2 | 28006 Madrid TEL +34 91 336 4266 E-MAIL stapia(a)industriales.upm.es www.industriales.upm.es

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Re: [boost] [cpo-proposal] presentation of the idea
by Santiago Tapia 10 Sep '13

10 Sep '13

> Date: Mon, 09 Sep 2013 11:57:43 -0500 > From: Larry Evans <cppljevans(a)suddenlink.net> > >> But because I am not an expert on alignment and memory >> optimization, I will try to use something "more standard", actually I am >> going trying to use the allocator to compute the "right" address to place >> an object of a given type that is greater that a "free" memory pointer. >> In that way, I also expect to take advantages of allocator such as >> tbb cache aligned allocator. > > I know nothing about how 'to use the allocator to compute the "right" > address'; hence, I'm afraid I can't be any help there. Could you maybe > give a brief summary of how that works? > No idea, I was just speculating, actually, I am not sure I will be able to do it. On the other hand, I suppose there should be a way to do it. Just need some time and thought. > Best of luck on this project, Santiago! > > -regards, > Larry Thank you!

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[PREPROCESSOR] Possible improvement for BOOST_PP_VARIADIC_SIZE
by Brent Lewis 10 Sep '13

10 Sep '13

Currently, BOOST_VARIADIC_SIZE() evaluates to 1. Based on http://gustedt.wordpress.com/2010/06/08/detect-empty-macro-arguments/ it can be improved to return 0 for an empty argument list.

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Quid pro quo for Boost peer review manager
by Niall Douglas 10 Sep '13

10 Sep '13

Dear Boost Devs, GSoC 2013 ends on 23rd September, and myself and Paul expect that Boost.AFIO will be ready for peer review at around that time after finishing the following features from your voting at http://boostafio.uservoice.com/: (i) Directory Monitoring (ii) Asynchronous Directory Enumeration (iii) Parts of Improved formal closure execution engine support based on the latest updated papers in the Sept WG21 mailing N3721 and N3731. It seems unfair to ask for someone to volunteer to do all the work to be a review manager for AFIO without me volunteering to be a review manager for another Boost library in exchange, so I was wondering: are there any similar sized libraries to AFIO (~800 active LOC, ~20,000 for everything including docs and testing) which are ready for peer review and need a review manager? Thanks, Niall -- Currently unemployed and looking for work. Work Portfolio: http://careers.stackoverflow.com/nialldouglas/

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[Thread] possible bug in Move emulation "portable interface"
by Gavin Lambert 09 Sep '13

09 Sep '13

I tried submitting this via Trac but for some reason it was convinced that my bug report contained spam, while refusing to tell me what part it was objecting to, and also refusing to give me a captcha or anything to convince it otherwise. Anyways: Bug 1: the Boost.Thread documentation and release history indicate that BOOST_THREAD_VERSION==3 is the default since v1.52. As far as I can tell this has never been true in any released version; the latest code still has ==2. (I found a thread in boost-devel that was debating consequences of making breaking changes by default, which I assume is why this change was not actually made; but the docs need correcting.) Bug 2: when writing code using the Boost.Thread "Portable Interface" for move support/emulation, it recommends using the BOOST_THREAD_DCL_MOVABLE_BEG macro to "avoid conflicts with Boost.Move". However regardless of C++11 or not or the BOOST_THREAD_VERSION it defines a template specialisation in a way that assumes that it is called only from "namespace boost". As this usage is unlikely for any code outside the boost library itself, I think this is a bug. namespace user { template<typename T> class test { public: BOOST_THREAD_COPYABLE_AND_MOVABLE(test) test() {} test(const test&) {} test& operator=(BOOST_COPY_ASSIGN_REF(test) o) { return *this; } test(BOOST_THREAD_RV_REF(test) o) {} test& operator=(BOOST_THREAD_RV_REF(test) o) { return *this; } }; BOOST_THREAD_DCL_MOVABLE_BEG(T) test<T> BOOST_THREAD_DCL_MOVABLE_END } The above code will not compile. It does compile if the DCL define is moved into a "namespace boost" block, but I do not regard this as an acceptable solution. Suggested fix is to explicitly specify the namespace in the macro, eg. replace "enable_move_utility_emulation" with "::boost::enable_move_utility_emulation".

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Fwd: Re: [atomic] atomic<int>::is_lock_free() returns false on iPad 4 (armv7s)
by Tim Blechmann 09 Sep '13

09 Sep '13

-------- Original-Nachricht -------- Betreff: Re: [boost] [atomic] atomic<int>::is_lock_free() returns false on iPad 4 (armv7s) Datum: Mon, 09 Sep 2013 15:49:06 +0100 Von: Phil Endecott <spam_from_boost_dev(a)chezphil.org> An: Tim Blechmann <tim(a)klingt.org> Hi Tim, (My Boost list subscription is temporarily broken; feel free to forward this if you want.) Tim Blechmann wrote: >>> boost:atomic<int>::is_lock_free() returns false on iPad 4 (armv7s) but >>> returns true on iPad 3 (armv7). Yes. I thought this had been fixed. It's now too long ago for me to recall exactly what happened. I know that I filed a trac ticket to get it fixed in smart_ptr's spinlock; I think that at that time Boost.Atomic has still not been reviewed and merged, and I probably fixed it only in a local copy. > btw, it may be worth to note that on iOS devices std::atomic should be > available ... Absolutely! Few people have any reason to be using Boost.Atomic. Regards, Phil.

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