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Implement is_always_lock_free
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Summary:

This was voted into C++17 at the Jacksonville meeting. The final P0152R1
paper will be in the upcoming post-Jacksonville mailing, and is also
available here:

  http://jfbastien.github.io/papers/P0152R1.html

Reviewers: mclow.lists, rsmith

Subscribers: cfe-commits

Differential Revision: http://reviews.llvm.org/D17951

llvm-svn: 264413
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@jfbastien
jfbastien committed Mar 25, 2016
1 parent 9706dcf commit b95ee81
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Showing 2 changed files with 133 additions and 11 deletions.
43 changes: 32 additions & 11 deletions libcxx/include/atomic
View file
Expand Up @@ -17,6 +17,10 @@
namespace std
{
// feature test macro
#define __cpp_lib_atomic_is_always_lock_free // as specified by SG10
// order and consistency
typedef enum memory_order
Expand Down Expand Up @@ -89,6 +93,7 @@ void
template <class T>
struct atomic
{
static constexpr bool is_always_lock_free;
bool is_lock_free() const volatile noexcept;
bool is_lock_free() const noexcept;
void store(T desr, memory_order m = memory_order_seq_cst) volatile noexcept;
Expand Down Expand Up @@ -127,6 +132,7 @@ struct atomic
template <>
struct atomic<integral>
{
static constexpr bool is_always_lock_free;
bool is_lock_free() const volatile noexcept;
bool is_lock_free() const noexcept;
void store(integral desr, memory_order m = memory_order_seq_cst) volatile noexcept;
Expand Down Expand Up @@ -202,6 +208,7 @@ struct atomic<integral>
template <class T>
struct atomic<T*>
{
static constexpr bool is_always_lock_free;
bool is_lock_free() const volatile noexcept;
bool is_lock_free() const noexcept;
void store(T* desr, memory_order m = memory_order_seq_cst) volatile noexcept;
Expand Down Expand Up @@ -540,6 +547,11 @@ void atomic_signal_fence(memory_order m) noexcept;
#error <atomic> is not implemented
#endif

#if _LIBCPP_STD_VER > 14
// FIXME: use the right feature test macro value as chose by SG10.
# define __cpp_lib_atomic_is_always_lock_free 201603L
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

typedef enum memory_order
Expand Down Expand Up @@ -825,13 +837,28 @@ kill_dependency(_Tp __y) _NOEXCEPT
return __y;
}

#define ATOMIC_BOOL_LOCK_FREE __GCC_ATOMIC_BOOL_LOCK_FREE
#define ATOMIC_CHAR_LOCK_FREE __GCC_ATOMIC_CHAR_LOCK_FREE
#define ATOMIC_CHAR16_T_LOCK_FREE __GCC_ATOMIC_CHAR16_T_LOCK_FREE
#define ATOMIC_CHAR32_T_LOCK_FREE __GCC_ATOMIC_CHAR32_T_LOCK_FREE
#define ATOMIC_WCHAR_T_LOCK_FREE __GCC_ATOMIC_WCHAR_T_LOCK_FREE
#define ATOMIC_SHORT_LOCK_FREE __GCC_ATOMIC_SHORT_LOCK_FREE
#define ATOMIC_INT_LOCK_FREE __GCC_ATOMIC_INT_LOCK_FREE
#define ATOMIC_LONG_LOCK_FREE __GCC_ATOMIC_LONG_LOCK_FREE
#define ATOMIC_LLONG_LOCK_FREE __GCC_ATOMIC_LLONG_LOCK_FREE
#define ATOMIC_POINTER_LOCK_FREE __GCC_ATOMIC_POINTER_LOCK_FREE

// general atomic<T>

template <class _Tp, bool = is_integral<_Tp>::value && !is_same<_Tp, bool>::value>
struct __atomic_base // false
{
mutable _Atomic(_Tp) __a_;

#if defined(__cpp_lib_atomic_is_always_lock_free)
static _LIBCPP_CONSTEXPR bool is_always_lock_free = __atomic_always_lock_free(sizeof(__a_), 0);
#endif

_LIBCPP_INLINE_VISIBILITY
bool is_lock_free() const volatile _NOEXCEPT
{
Expand Down Expand Up @@ -920,6 +947,11 @@ private:
#endif // _LIBCPP_HAS_NO_DELETED_FUNCTIONS
};

#if defined(__cpp_lib_atomic_is_always_lock_free)
template <class _Tp, bool __b>
_LIBCPP_CONSTEXPR bool __atomic_base<_Tp, __b>::is_always_lock_free;
#endif

// atomic<Integral>

template <class _Tp>
Expand Down Expand Up @@ -1789,17 +1821,6 @@ typedef atomic<uintmax_t> atomic_uintmax_t;
#define ATOMIC_FLAG_INIT {false}
#define ATOMIC_VAR_INIT(__v) {__v}

#define ATOMIC_BOOL_LOCK_FREE __GCC_ATOMIC_BOOL_LOCK_FREE
#define ATOMIC_CHAR_LOCK_FREE __GCC_ATOMIC_CHAR_LOCK_FREE
#define ATOMIC_CHAR16_T_LOCK_FREE __GCC_ATOMIC_CHAR16_T_LOCK_FREE
#define ATOMIC_CHAR32_T_LOCK_FREE __GCC_ATOMIC_CHAR32_T_LOCK_FREE
#define ATOMIC_WCHAR_T_LOCK_FREE __GCC_ATOMIC_WCHAR_T_LOCK_FREE
#define ATOMIC_SHORT_LOCK_FREE __GCC_ATOMIC_SHORT_LOCK_FREE
#define ATOMIC_INT_LOCK_FREE __GCC_ATOMIC_INT_LOCK_FREE
#define ATOMIC_LONG_LOCK_FREE __GCC_ATOMIC_LONG_LOCK_FREE
#define ATOMIC_LLONG_LOCK_FREE __GCC_ATOMIC_LLONG_LOCK_FREE
#define ATOMIC_POINTER_LOCK_FREE __GCC_ATOMIC_POINTER_LOCK_FREE

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP_ATOMIC
101 changes: 101 additions & 0 deletions libcxx/test/std/atomics/atomics.lockfree/isalwayslockfree.pass.cpp
View file
@@ -0,0 +1,101 @@
//===----------------------------------------------------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// UNSUPPORTED: libcpp-has-no-threads, c++98, c++03, c++11, c++14

// <atomic>

// static constexpr bool is_always_lock_free;

#include <atomic>
#include <cassert>

#if !defined(__cpp_lib_atomic_is_always_lock_free)
# error Feature test macro missing.
#endif

template <typename T> void checkAlwaysLockFree() {
if (std::atomic<T>::is_always_lock_free)
assert(std::atomic<T>().is_lock_free());
}

int main()
{
// structs and unions can't be defined in the template invocation.
// Work around this with a typedef.
#define CHECK_ALWAYS_LOCK_FREE(T) \
do { \
typedef T type; \
checkAlwaysLockFree<type>(); \
} while (0)

CHECK_ALWAYS_LOCK_FREE(bool);
CHECK_ALWAYS_LOCK_FREE(char);
CHECK_ALWAYS_LOCK_FREE(signed char);
CHECK_ALWAYS_LOCK_FREE(unsigned char);
CHECK_ALWAYS_LOCK_FREE(char16_t);
CHECK_ALWAYS_LOCK_FREE(char32_t);
CHECK_ALWAYS_LOCK_FREE(wchar_t);
CHECK_ALWAYS_LOCK_FREE(short);
CHECK_ALWAYS_LOCK_FREE(unsigned short);
CHECK_ALWAYS_LOCK_FREE(int);
CHECK_ALWAYS_LOCK_FREE(unsigned int);
CHECK_ALWAYS_LOCK_FREE(long);
CHECK_ALWAYS_LOCK_FREE(unsigned long);
CHECK_ALWAYS_LOCK_FREE(long long);
CHECK_ALWAYS_LOCK_FREE(unsigned long long);
CHECK_ALWAYS_LOCK_FREE(std::nullptr_t);
CHECK_ALWAYS_LOCK_FREE(void*);
CHECK_ALWAYS_LOCK_FREE(float);
CHECK_ALWAYS_LOCK_FREE(double);
CHECK_ALWAYS_LOCK_FREE(long double);
CHECK_ALWAYS_LOCK_FREE(int __attribute__((vector_size(1 * sizeof(int)))));
CHECK_ALWAYS_LOCK_FREE(int __attribute__((vector_size(2 * sizeof(int)))));
CHECK_ALWAYS_LOCK_FREE(int __attribute__((vector_size(4 * sizeof(int)))));
CHECK_ALWAYS_LOCK_FREE(int __attribute__((vector_size(16 * sizeof(int)))));
CHECK_ALWAYS_LOCK_FREE(int __attribute__((vector_size(32 * sizeof(int)))));
CHECK_ALWAYS_LOCK_FREE(float __attribute__((vector_size(1 * sizeof(float)))));
CHECK_ALWAYS_LOCK_FREE(float __attribute__((vector_size(2 * sizeof(float)))));
CHECK_ALWAYS_LOCK_FREE(float __attribute__((vector_size(4 * sizeof(float)))));
CHECK_ALWAYS_LOCK_FREE(float __attribute__((vector_size(16 * sizeof(float)))));
CHECK_ALWAYS_LOCK_FREE(float __attribute__((vector_size(32 * sizeof(float)))));
CHECK_ALWAYS_LOCK_FREE(double __attribute__((vector_size(1 * sizeof(double)))));
CHECK_ALWAYS_LOCK_FREE(double __attribute__((vector_size(2 * sizeof(double)))));
CHECK_ALWAYS_LOCK_FREE(double __attribute__((vector_size(4 * sizeof(double)))));
CHECK_ALWAYS_LOCK_FREE(double __attribute__((vector_size(16 * sizeof(double)))));
CHECK_ALWAYS_LOCK_FREE(double __attribute__((vector_size(32 * sizeof(double)))));
CHECK_ALWAYS_LOCK_FREE(struct{});
CHECK_ALWAYS_LOCK_FREE(struct{ int i; });
CHECK_ALWAYS_LOCK_FREE(struct{ int i[2]; });
CHECK_ALWAYS_LOCK_FREE(struct{ long long int i[2]; });
CHECK_ALWAYS_LOCK_FREE(struct{ long long int i[4]; });
CHECK_ALWAYS_LOCK_FREE(struct{ long long int i[8]; });
CHECK_ALWAYS_LOCK_FREE(struct{ long long int i[16]; });
CHECK_ALWAYS_LOCK_FREE(struct{ char c; /* padding */ long long int i; });
CHECK_ALWAYS_LOCK_FREE(union{ int i; float f; });

// C macro and static constexpr must be consistent.
static_assert(std::atomic<bool>::is_always_lock_free == (2 == ATOMIC_BOOL_LOCK_FREE));
static_assert(std::atomic<char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
static_assert(std::atomic<signed char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
static_assert(std::atomic<unsigned char>::is_always_lock_free == (2 == ATOMIC_CHAR_LOCK_FREE));
static_assert(std::atomic<char16_t>::is_always_lock_free == (2 == ATOMIC_CHAR16_T_LOCK_FREE));
static_assert(std::atomic<char32_t>::is_always_lock_free == (2 == ATOMIC_CHAR32_T_LOCK_FREE));
static_assert(std::atomic<wchar_t>::is_always_lock_free == (2 == ATOMIC_WCHAR_T_LOCK_FREE));
static_assert(std::atomic<short>::is_always_lock_free == (2 == ATOMIC_SHORT_LOCK_FREE));
static_assert(std::atomic<unsigned short>::is_always_lock_free == (2 == ATOMIC_SHORT_LOCK_FREE));
static_assert(std::atomic<int>::is_always_lock_free == (2 == ATOMIC_INT_LOCK_FREE));
static_assert(std::atomic<unsigned int>::is_always_lock_free == (2 == ATOMIC_INT_LOCK_FREE));
static_assert(std::atomic<long>::is_always_lock_free == (2 == ATOMIC_LONG_LOCK_FREE));
static_assert(std::atomic<unsigned long>::is_always_lock_free == (2 == ATOMIC_LONG_LOCK_FREE));
static_assert(std::atomic<long long>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE));
static_assert(std::atomic<unsigned long long>::is_always_lock_free == (2 == ATOMIC_LLONG_LOCK_FREE));
static_assert(std::atomic<void*>::is_always_lock_free == (2 == ATOMIC_POINTER_LOCK_FREE));
static_assert(std::atomic<std::nullptr_t>::is_always_lock_free == (2 == ATOMIC_POINTER_LOCK_FREE));
}

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