Re: [Boost-users] Weird code in lockfree::queue::reserve (compilation error)
On 04/02/2016 05:08 PM, Aurelien Regat-Barrel wrote:
I'm trying to use lockfree::queue, and I get a compiler error when calling reserve(). The following code does not compile with VC++ 2015:
What error are you getting? Have you checked that the type T you use as the template argument to lockfree::queue<T> fulfills the documented requirements?
void reserve(size_type n) { pool.template reserve<true>(n); }
And indeed... what does this syntax mean: "pool.template reserve"? You can see it here:
The use of the template keyword above is correct. It is used to help the C++ compiler resolve an otherwise ambiguous syntax. See the section "The template disambiguator for dependent names" at: http://en.cppreference.com/w/cpp/language/dependent_name
Hello,
What error are you getting?
VC++ 2015 emits a syntax error: void f() { boost::lockfree::queue<int*, boost::lockfree::fixed_sized<true>> queue; queue.reserve(10); } 1>boost\lockfree\queue.hpp(226): error C2059: syntax error: 'template' I figured out this is because of the "boost::lockfree::fixed_sized<true>" option. If I removed it, it compiles fine. So I managed to set the size of my queue at construction time. Do you think it would be possible to improve the error message? === Bonus! === I was using VC++ 2015 Update 1, and I just updated to Update 2... and I get another error from std::atomic: #ifndef _ENABLE_ATOMIC_ALIGNMENT_FIX static_assert(alignof(_Ty) >= alignof(_My_int), "You've instantiated std::atomic<T> with sizeof(T) equal to 2/4/8 and alignof(T) < sizeof(T). " "Before VS 2015 Update 2, this would have misbehaved at runtime. " "VS 2015 Update 2 was fixed to handle this correctly, " "but the fix inherently changes layout and breaks binary compatibility. " "Please define _ENABLE_ATOMIC_ALIGNMENT_FIX to acknowledge that you understand this, " "and that everything you're linking has been compiled with VS 2015 Update 2 (or later)."); #endif /* _ENABLE_ATOMIC_ALIGNMENT_FIX */ This is caused by the following code in boost\lockfree\detail\freelist.hpp(603): std::atomic<boost::lockfree::detail::tagged_index> pool_; with sizeof(tagged_index) == 4 and alignof(tagged_index) == 2. It can be fixed by changing tagged_index to be alignas(4), or by defining _ENABLE_ATOMIC_ALIGNMENT_FIX: #if _MSC_FULL_VER == 190023918 // VC++ 2015 Update 2 #define _ENABLE_ATOMIC_ALIGNMENT_FIX #endif Since there's a compiler bug prior to Update 2 (https://connect.microsoft.com/VisualStudio/feedback/details/1892487/code-gen...), may be the source should be updated to not compile if the code generated by VC++ is not reliable? Regards, Aurélien Regat-Barrel
participants (3)
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Aurelien Regat-Barrel -
Bjorn Reese