00f4a49b0b
Summary: After putting this question up on cfe-dev I have decided that it would be best to allow the use of `<atomic>` in C++03. Although static initialization is a concern the syntax required to get it is C++11 only. Meaning that C++11 constant static initialization cannot silently break in C++03, it will always cause a syntax error. Furthermore `ATOMIC_VAR_INIT` and `ATOMIC_FLAG_INIT` remain defined in C++03 even though they cannot be used because C++03 usages will cause better error messages. The main change in this patch is to replace `__has_feature(cxx_atomic)`, which only returns true when C++ >= 11, to `__has_extension(c_atomic)` which returns true whenever clang supports the required atomic builtins. This patch adds the following macros: * `_LIBCPP_HAS_C_ATOMIC_IMP` - Defined on clang versions which provide the C `_Atomic` keyword. * `_LIBCPP_HAS_GCC_ATOMIC_IMP` - Defined on GCC > 4.7. We must use the fallback atomic implementation. * `_LIBCPP_HAS_NO_ATOMIC_HEADER` - Defined when it is not safe to include `<atomic>`. `_LIBCPP_HAS_C_ATOMIC_IMP` and `_LIBCPP_HAS_GCC_ATOMIC_IMP` are mutually exclusive, only one should be defined. If neither is defined then `<atomic>` is not implemented and including `<atomic>` will issue an error. Reviewers: chandlerc, jroelofs, mclow.lists Subscribers: cfe-commits Differential Revision: http://reviews.llvm.org/D11555 git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@245463 91177308-0d34-0410-b5e6-96231b3b80d8
27 lines
626 B
C++
27 lines
626 B
C++
//===----------------------------------------------------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is dual licensed under the MIT and the University of Illinois Open
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// Source Licenses. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// UNSUPPORTED: libcpp-has-no-threads
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// XFAIL: c++98, c++03
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// <atomic>
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// struct atomic_flag
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// atomic_flag() = ATOMIC_FLAG_INIT;
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#include <atomic>
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#include <cassert>
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int main()
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{
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std::atomic_flag f = ATOMIC_FLAG_INIT;
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assert(f.test_and_set() == 0);
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}
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