jfb created this revision.
jfb added reviewers: mclow.lists, rsmith.
jfb added a subscriber: cfe-commits.
This was voted into C++17 at last week's 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
The clang part of this implementation is in the following code review:
http://reviews.llvm.org/D17950
http://reviews.llvm.org/D17951
Files:
include/atomic
test/std/atomics/atomics.lockfree/lockfree.pass.cpp
Index: test/std/atomics/atomics.lockfree/lockfree.pass.cpp
===================================================================
--- test/std/atomics/atomics.lockfree/lockfree.pass.cpp
+++ test/std/atomics/atomics.lockfree/lockfree.pass.cpp
@@ -11,20 +11,30 @@
// <atomic>
+// #define ATOMIC_BOOL_LOCK_FREE unspecified
// #define ATOMIC_CHAR_LOCK_FREE unspecified
// #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
// #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
// #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
// #define ATOMIC_SHORT_LOCK_FREE unspecified
// #define ATOMIC_INT_LOCK_FREE unspecified
// #define ATOMIC_LONG_LOCK_FREE unspecified
// #define ATOMIC_LLONG_LOCK_FREE unspecified
+// #define ATOMIC_POINTER_LOCK_FREE unspecified
#include <atomic>
#include <cassert>
+template <typename T> void checkAlwaysLockFree() {
+ if (std::atomic<T>::is_always_lock_free)
+ assert(std::atomic<T>().is_lock_free());
+}
+
int main()
{
+ assert(ATOMIC_BOOL_LOCK_FREE == 0 ||
+ ATOMIC_BOOL_LOCK_FREE == 1 ||
+ ATOMIC_BOOL_LOCK_FREE == 2);
assert(ATOMIC_CHAR_LOCK_FREE == 0 ||
ATOMIC_CHAR_LOCK_FREE == 1 ||
ATOMIC_CHAR_LOCK_FREE == 2);
@@ -49,4 +59,60 @@
assert(ATOMIC_LLONG_LOCK_FREE == 0 ||
ATOMIC_LLONG_LOCK_FREE == 1 ||
ATOMIC_LLONG_LOCK_FREE == 2);
+ assert(ATOMIC_POINTER_LOCK_FREE == 0 ||
+ ATOMIC_POINTER_LOCK_FREE == 1 ||
+ ATOMIC_POINTER_LOCK_FREE == 2);
+
+// 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; });
}
Index: include/atomic
===================================================================
--- include/atomic
+++ include/atomic
@@ -89,6 +89,7 @@
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;
@@ -127,6 +128,7 @@
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;
@@ -202,6 +204,7 @@
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;
@@ -825,13 +828,81 @@
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
+
+#if defined(__cpp_lib_atomic_is_always_lock_free)
+# if defined(__LLVM_LOCK_FREE_IS_SIZE_BASED) && __LLVM_LOCK_FREE_IS_SIZE_BASED == 1
+# define _LIBCPP_LOCK_FREE_IS_SIZE_BASED
+template <int _Bytes> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free = false;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<1> = __LLVM_ATOMIC_1_BYTES_LOCK_FREE == 2;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<2> = __LLVM_ATOMIC_2_BYTES_LOCK_FREE == 2;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<4> = __LLVM_ATOMIC_4_BYTES_LOCK_FREE == 2;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<8> = __LLVM_ATOMIC_8_BYTES_LOCK_FREE == 2;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<16> = __LLVM_ATOMIC_16_BYTES_LOCK_FREE == 2;
+# else
+template <typename T> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free = false;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<bool> = 2 == ATOMIC_BOOL_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<char> = 2 == ATOMIC_CHAR_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<signed char> = 2 == ATOMIC_CHAR_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<unsigned char> = 2 == ATOMIC_CHAR_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<char16_t> = 2 == ATOMIC_CHAR16_T_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<char32_t> = 2 == ATOMIC_CHAR32_T_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<wchar_t> = 2 == ATOMIC_WCHAR_T_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<short> = 2 == ATOMIC_SHORT_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<unsigned short> = 2 == ATOMIC_SHORT_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<int> = 2 == ATOMIC_INT_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<unsigned int> = 2 == ATOMIC_INT_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<long> = 2 == ATOMIC_LONG_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<unsigned long> = 2 == ATOMIC_LONG_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<long long> = 2 == ATOMIC_LLONG_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<unsigned long long> = 2 == ATOMIC_LLONG_LOCK_FREE;
+template <typename T> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<T*> = 2 == ATOMIC_POINTER_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<std::nullptr_t> = 2 == ATOMIC_POINTER_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<float> =
+# if defined(__GCC_ATOMIC_FLOAT_LOCK_FREE) && 2 == __GCC_ATOMIC_FLOAT_LOCK_FREE
+ true;
+# else
+ false;
+# endif
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<double> =
+# if defined(__GCC_ATOMIC_DOUBLE_LOCK_FREE) && 2 == __GCC_ATOMIC_DOUBLE_LOCK_FREE
+ true;
+# else
+ false;
+# endif
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<long double> =
+# if defined(__GCC_ATOMIC_LDOUBLE_LOCK_FREE) && 2 == __GCC_ATOMIC_LDOUBLE_LOCK_FREE
+ true;
+# else
+ false;
+# endif
+# endif
+#endif
+
// 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)
+# if defined(_LIBCPP_LOCK_FREE_IS_SIZE_BASED)
+ static _LIBCPP_CONSTEXPR bool is_always_lock_free = __libcpp_always_lock_free<sizeof(_Tp)>;
+# else
+ static _LIBCPP_CONSTEXPR bool is_always_lock_free = __libcpp_always_lock_free<_Tp>;
+# endif
+#endif
+
_LIBCPP_INLINE_VISIBILITY
bool is_lock_free() const volatile _NOEXCEPT
{
@@ -1789,17 +1860,6 @@
#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
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