[boost-asio] Add package option to enable io_uring support

[gracicot]

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Is your feature request related to a problem? Please describe.

The next boost asio (version 1.78) has an option for enabling io_uring. It must be compiled with BOOST_ASIO_HAS_IO_URING and BOOST_ASIO_DISABLE_EPOLL

Proposed solution An installation option to enable uring

Describe alternatives you've considered The two options could also be enabled/disabled to selectively enable uring, epoll, or both.

Additional context Boost 1.78 is out: https://www.boost.org/doc/libs/1_78_0/doc/html/boost_asio/history.html

[yurybura]

Boost.Asio is header only library. You can add these defines in your application.

[gracicot]

@yurybura As far as I know changing options would change the interface requirement for boost asio, which would apply to all packages using it. Simply using a define because it's header only don't cut it. If you have a dependency that use boost asio and you define those keyword in your project, you'll have ODR violation. The package manager should take care of that.

[yurybura]

The Boost packages are compatible with built-in CMake targets:

find_package(Boost REQUIRED [COMPONENTS <libs>...])
target_link_libraries(main PRIVATE Boost::boost Boost::<lib1> Boost::<lib2> ...)

vcpkg doesn't provide any other exported CMake target.

Due to boost-asio doesn't have binary files I think you can simply build your own application like this:

 find_package(Boost REQUIRED)
 target_link_libraries(main PRIVATE Boost::boost)
 target_compile_definitions(main 
    PRIVATE
        BOOST_ASIO_HAS_IO_URING=1
        BOOST_ASIO_DISABLE_EPOLL=1
 )

If another vcpkg port will use io_uring at build time, that package should have similar CMake code in portfile.cmake.

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[gracicot]

I don't think this issue should be closed simply because there was no comments. I think it would be valuable to have a port feature for boost asio to enable io_uring. It is a header only library yes, but I don't think it's really relevant for this issue. If consistency, avoiding ODR violations and one day enable C++20 module builds is something vcpkg users want, it should be port feature.