March 2019 - Boost - lists.preview.boost.org

[asio][coroutine] forbid_suspend blocks
by Vinícius dos Santos Oliveira 07 Aug '19

07 Aug '19

I've implemented a dumb linter using Python + clang API that allows you to mark certain blocks as “atomic in respect to coroutines” using C++11 attributes. Usage example follows: void f() { int yield; g(yield); [[bt::forbid_suspend]] { // Comment this call to make linter accept the code g(yield); t(); } } You can change bt::forbid_suspend to another identifier by tuning settings on the beginning of the script. The prefix forbid was inspired by Rust's linters[1] as you cannot disallow the linter from inside the forbid_suspend block. Some limitations follow: - A suspend point is identified by looking references to any id equals to yield in the last argument passed to function calls. It means that yield[ignored_ec] and alike will be correctly identified, but it needs to be named yield and it needs to be the last argument to the function call. - I haven't found a way to extract attributes related to COMPOUND_STMT nodes with clang API, so I manually look for token gaps and do a simple regex. It means you cannot use macros to [[bt::forbid_suspend]] as the macro won't be expanded. - You better call the script with '-x c++' and also ' -I/usr/lib/clang/5.0.1/include'. Like I've said in the beginning of the email, it's a *dumb* linter, which means it doesn't try to handle all cases. Therefore, I don't hope to do many changes to it or maintain it to work against newer releases of clang and I'm only uploading it to gist (not fullblow Github): < https://gist.github.com/vinipsmaker2/d930fbe5b7597432b021effe618da171>. It should also be easy to hack as it is very small. I'm releasing the linter under public domain. Enjoy. I have been using fibers in a daily basis on the last months of my job to solve networking problems on a gateway project. Some of the technologies I use are: - Boost.Asio and its spawn function. - A few custom synchronization primitives for the fibers (e.g. mutex, semaphore). - Eventually I'll have to write a custom spawn function that returns a joinable handle so I can kill the usage of a fiber::barrier in a few places. I've been using the linter for about a week already and looks fine. My use case are: - To prevent iterator invalidation in regions accessing shared variables. - To guarantee events order in algorithms that handle races (cannot yield while task YYY hasn't finished). The project I use it in is not an open source project, so I cannot talk much more about it. Also, I don't claim my solution is original. I wouldn't be surprised if the very same solution exists in the wild (please let me know if you know of a similar approach). This is not a new problem. It is know for some time. For instance, in P0171, Gor Nishanov noted this same problem: “In coroutines the suspend point is clearly marked with await, which tells the reader that something unusual happens in this function and allows the reader, for example, to confirm whether the lifetimes of the objects of interest align with the lifetime of the coroutine or not, whether some locks need to be acquired to protect some concurrently accessed data, and whether some locks need to be released before the execution reaches the suspend point.” — <http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0171r0.html>, 2015 However, the solution he presented was to manually examine whole blocks of code without help from the compiler. I argue that the solution he presented is as error-prone as manually looking for exit paths that don't free acquired resources in languages lacking RAII. And I've been spoiled too much by RAII. Furthermore, I take this comment of his with highly suspicious look: “Since we are on the subject of maintenance nightmares, we would like to offer a conjecture that the absence of the await in P0114 is a likely source of many maintenance nightmares. Without a syntactic marker to signal to the person reading the code that something funny is going on, it is impossible to tell whether the following code is correct or not” — http://open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0171r0.html If I had to give a vote to the proposal he was defending or Chris' proposal, I'd probably have chosen Chris'. [1] https://doc.rust-lang.org/reference/attributes.html# lint-check-attributes -- Vinícius dos Santos Oliveira https://vinipsmaker.github.io/

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Non-ASCII Path Names in Repo
by Tom Kent 25 May '19

25 May '19

In the last few days we've had a non-ASCII path name added to the repo: tools/boostdep/test/utf8-test-ßµ™∃ Which came with commit 8893d1c57951a [1] I noticed this because a python 2 script (calling shutil.copytree) I had running on windows that copied the repo around started to fail. I've long needed to update that script to python 3, and am working on this. However, I wanted to point this out to the list so we could discuss if there are any other ramifications of having a non-ascii path. I vaguely remember some discussion about something like this in the past, but couldn't find it via search. If this is already a settled topic, that's great. Tom [1] https://github.com/boostorg/boostdep/commit/8893d1c57951a4a83705ed203005576…

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Re: [boost] [ Interest? ] [ out_ptr ] Tiny C++ Abstraction for C-Style Output Pointers
by Bjorn Reese 12 May '19

12 May '19

On 06/28/18 21:03, ThePhD via Boost wrote: > out_ptr is a small abstraction for making types such as > std::unique_ptr, std::shared_ptr, boost::shared_ptr, and the upcoming > std::retain_ptr > <http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0468r0.html> work > work C-Style output functions as a parameter, addressing the need of > wanting to be able to do "my_c_api_init( foo, bar, &my_smart_ptr );". It's Does out_ptr have other use-cases than C interoperability?

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[thread] compiler error gcc 7.3 on cygwin
by James E. King III 06 May '19

06 May '19

Getting an internal compiler error with gcc 7.3 but only on cygwin 64-bit. Jim@pulsar /cygdrive/c/boost/libs/thread $ ../../b2 --abbreviate-paths toolset=gcc cxxstd=11 define=_POSIX_C_SOURCE=200112L define=__USE_ISOC99 threadapi=pthread address-model=64 variant=release -q ... gcc.compile.c++ ../../bin.v2/libs/thread/test/test_10963_c.test/gcc-7.3.0/rls/cxstd-11-iso/thrd-mlt/vsblt-hdn/test_10963_c.o In file included from ../../boost/thread/detail/invoker.hpp:30:0, from ../../boost/thread/future.hpp:31, from ../../libs/thread/test/test_10963.cpp:13: ../../boost/thread/detail/invoke.hpp: In function ‘decltype (*(forward<A0>)(boost::detail::invoke::a0).*boost::detail::invoke::f) boost::detail::invoke(Fp&&, A0&&) [with Fp = void (boost::executors::basic_thread_pool::*)(); A0 = boost::executors::basic_thread_pool*]’: ../../boost/thread/detail/invoke.hpp:102:43: internal compiler error: in gimplify_expr, at gimplify.c:12006 return (*boost::forward<A0>(a0)).*f; ^ Please submit a full bug report, with preprocessed source if appropriate. See <https://gcc.gnu.org/bugs/> for instructions. "g++" -std=c++11 -fvisibility-inlines-hidden -m64 -mthreads -O3 -finline-functions -Wno-inline -Wall -pedantic -fvisibility=hidden -Wextra -Wno-long-long -Wno-unused-parameter -Wunused-function -pedantic -DBOOST_ALL_NO_LIB=1 -DBOOST_THREAD_THROW_IF_PRECONDITION_NOT_SATISFIED -DNDEBUG -D_POSIX_C_SOURCE=200112L -D__USE_ISOC99 -I"../.." -c -o "../../bin.v2/libs/thread/test/test_10963_c.test/gcc-7.3.0/rls/cxstd-11-iso/thrd-mlt/vsblt-hdn/test_10963_c.o" "../../libs/thread/test/test_10963.cpp" ...failed gcc.compile.c++ ../../bin.v2/libs/thread/test/test_10963_c.test/gcc-7.3.0/rls/cxstd-11-iso/thrd-mlt/vsblt-hdn/test_10963_c.o... If I change the C++ language level to 03 the problem goes away. I also cannot reproduce it on linux with the same version of compiler (but it probably isn't the exact same compiler code). Should I go ahead and file that gcc bug? - Jim

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[review][variant2] Variant2 Review Starts April 1
by Michael Caisse 06 Apr '19

06 Apr '19

The Boost formal review of Peter Dimov's Variant2 library will take place April 1 - 10, 2019. Please consider participating in this review. The success of Boost is partially a result of the quality review process which is conducted by the community. You are part of the Boost community. I will be grateful to receive a review based on whatever level of effort or time you can devote. Variant2 is a never-valueless C++11/14/17 implementation of std::variant. >From the README: The class boost::variant2::variant<T...> is an almost conforming implementation of std::variant with the following differences: * A converting constructor from, e.g. variant<int, float> to variant<float, double, int> is provided as an extension; * The reverse operation, going from variant<float, double, int> to variant<int, float> is provided as the member function subset<U...>. (This operation can throw if the current state of the variant cannot be represented.) * variant<T...> is not trivial when all contained types are trivial. To avoid going into a valueless-by-exception state, this implementation falls back to using double storage unless * one of the alternatives is the type monostate, * one of the alternatives has a nonthrowing default constructor, or * all the contained types are nothrow move constructible. If the first two bullets don't hold, but the third does, the variant uses single storage, but emplace constructs a temporary and moves it into place if the construction of the object can throw. In case this is undesirable, one can force emplace into always constructing in- place by adding monostate as one of the alternatives. You can find the source code here: <https://github.com/pdimov/variant2> and the documentation here: <https://pdimov.github.io/variant2/doc/html/variant2.html> Please take an early look at the library and ask questions now. Peter Dimov is very active on the Cpplang Slack #boost channel; however, please consider using the Boost Dev or User Mail Lists so that the entire community might benefit from your conversation. Note: The repository contains an expected implementation also; however, that is not being considered in this review. Thank you for your participation! michael -- Michael Caisse Ciere Consulting ciere.com

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GSoC'19 [Boost.Geometry : Implementing algorithms for the concave hull problem]
by yaghyavardhan singh khangarot 06 Apr '19

06 Apr '19

Hi, I am interested in contributing to Boost.Geometry and would like to work on the Project 1 (Implementing algorithms for the concave hull problem) as my GsoC’19 project. I had some discussion regarding this with Adam Wulkiewicz. I have read the paper ( Moreira, Adriano J. C., and Maribel Yasmina Santos. “Concave hull: A k-nearest neighbors approach for the computation of the region occupied by a set of points.”) and currently going through the paper “A New Concave Hull Algorithm and Concaveness Measure for n-dimensional Datasets*” ( https://www.iis.sinica.edu.tw/page/jise/2012/201205_10.pdf )) . These are the papers given in the project description. I am also searching for any other algorithms (newer or better) for the concave hull problem. Please direct me to any other algorithms related to this project. Regards Yaghyavardhan

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Master branch open for merging
by Marshall Clow 03 Apr '19

03 Apr '19

The master branch is is now open for post-beta merges, but only as described in the Post-Beta Merge Policy. See < https://github.com/boostorg/boost/wiki/Releases%3A-Beta-Merge-Policy> -- The Boost Release Team

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[gsoc19] Seeking a mentor for Boost.GIL project
by Igor Antropov 02 Apr '19

02 Apr '19

DearSir/Madam, My name isIgor Antropov and I would like to participate in GSoC 2019.I amfirst-year undergraduate master majoring in Software Engineering at ITMOUniversity (Saint Petersburg National Research University of Information Technologies,Mechanics and Optics).I aminterested in computer vision and C++. I have made AR-application using Unityand OpenCVForUnity at my third-year of bachelor degree. Unfortunately, thatOpenCVForUnity was based on OpenCV version 2.1 or smaller and was the only onefree to use. There was no algorithm for markers detection, so I had to codeit. At the fourth-year, I have implementobject tracking algorithm with C++ and OpenCV using HOG features and colornames features. Additionally, I havebeen working as programmer with Qt for 1 year. I aminterested in implementation of different algorithms using GIL, so I propose toimplement some image feature detection and matching algorithms. For example,ORB keypoints detector(http://www.willowgarage.com/sites/default/files/orb_final.pdf) and brute-forcematching. Besides, I think Boost.GIL numeric algorithms can have some improvements (add 2D convolution, add convolve_option_extend_reflect as convolve_boundary_options). If Boost.GIL users need some other algorithms to be implemented,please contact me. As my competencytest, I have implement a simple Canny edge detection algorithm using GIL. https://github.com/boostorg/gil/pull/258 Sincerely, IgorAntropov

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[gsoc19] Seeking a mentor for Boost.Geometry project related to triangulation and random sampling
by Tinko Bartels 01 Apr '19

01 Apr '19

Hi, I am interested in participating in this year's Google Summer of Code with a contribution to Boost.Geometry. I am looking for mentors and I understand that potential mentors for Boost.Geometry-related projects are Vissarion Fysikopoulos and Adam Wulkiewicz. My proposal is a project that is based on project 3 and 4 for Boost.Geometry in the Wiki. I propose to add concepts for triangles, triangulation, and point-generators for random sampling, as well as corresponding models and an algorithm for Delaunay-triangulation with parametrizable geometric predicates. The first draft of my proposal can be found here: https://docs.google.com/document/d/17M44Hpn0KMuECztCbkvTYIeN2EiXbMAUsVni22K… My implementation of the tasks in the competency tests can be found here: https://tinko92.github.io/boost_geometry_GSoC_2019_project_3_4_test/ I'd be thankful for any feedback. Kind regards, Tinko Bartels -- Sent from: http://boost.2283326.n4.nabble.com/Boost-Dev-f2600599.html

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[format] Allow the format library to use std::optional
by Sean Farrow 30 Mar '19

30 Mar '19

Hi, Would be possible/desired to allow boost.format to use std::optional instead of boost.optional when compiling a C++17 project. I've raised a GitHub issue to resolve this: https://github.com/boostorg/format/issues/63 I would be happy to do this if it were warranted. Kind regards Sean.

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