diff options
Diffstat (limited to 'absl/base/internal/atomic_hook.h')
| -rw-r--r-- | absl/base/internal/atomic_hook.h | 57 |
1 files changed, 45 insertions, 12 deletions
diff --git a/absl/base/internal/atomic_hook.h b/absl/base/internal/atomic_hook.h index 6757e75b..ae21cd7f 100644 --- a/absl/base/internal/atomic_hook.h +++ b/absl/base/internal/atomic_hook.h @@ -11,7 +11,6 @@ // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. -// #ifndef ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ #define ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ @@ -21,29 +20,51 @@ #include <cstdint> #include <utility> -#ifdef _MSC_FULL_VER +#include "absl/base/attributes.h" +#include "absl/base/config.h" + +#if defined(_MSC_VER) && !defined(__clang__) +#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 0 +#else +#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 1 +#endif + +#if defined(_MSC_VER) #define ABSL_HAVE_WORKING_ATOMIC_POINTER 0 #else #define ABSL_HAVE_WORKING_ATOMIC_POINTER 1 #endif namespace absl { -inline namespace lts_2019_08_08 { +ABSL_NAMESPACE_BEGIN namespace base_internal { template <typename T> class AtomicHook; -// AtomicHook is a helper class, templatized on a raw function pointer type, for -// implementing Abseil customization hooks. It is a callable object that -// dispatches to the registered hook. +// To workaround AtomicHook not being constant-initializable on some platforms, +// prefer to annotate instances with `ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES` +// instead of `ABSL_CONST_INIT`. +#if ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT +#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES ABSL_CONST_INIT +#else +#define ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES +#endif + +// `AtomicHook` is a helper class, templatized on a raw function pointer type, +// for implementing Abseil customization hooks. It is a callable object that +// dispatches to the registered hook. Objects of type `AtomicHook` must have +// static or thread storage duration. // // A default constructed object performs a no-op (and returns a default // constructed object) if no hook has been registered. // -// Hooks can be pre-registered via constant initialization, for example, -// ABSL_CONST_INIT static AtomicHook<void(*)()> my_hook(DefaultAction); -// and then changed at runtime via a call to Store(). +// Hooks can be pre-registered via constant initialization, for example: +// +// ABSL_INTERNAL_ATOMIC_HOOK_ATTRIBUTES static AtomicHook<void(*)()> +// my_hook(DefaultAction); +// +// and then changed at runtime via a call to `Store()`. // // Reads and writes guarantee memory_order_acquire/memory_order_release // semantics. @@ -58,12 +79,23 @@ class AtomicHook<ReturnType (*)(Args...)> { // Constructs an object that by default dispatches to/returns the // pre-registered default_fn when no hook has been registered at runtime. -#if ABSL_HAVE_WORKING_ATOMIC_POINTER +#if ABSL_HAVE_WORKING_ATOMIC_POINTER && ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT explicit constexpr AtomicHook(FnPtr default_fn) : hook_(default_fn), default_fn_(default_fn) {} -#else +#elif ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT explicit constexpr AtomicHook(FnPtr default_fn) : hook_(kUninitialized), default_fn_(default_fn) {} +#else + // As of January 2020, on all known versions of MSVC this constructor runs in + // the global constructor sequence. If `Store()` is called by a dynamic + // initializer, we want to preserve the value, even if this constructor runs + // after the call to `Store()`. If not, `hook_` will be + // zero-initialized by the linker and we have no need to set it. + // https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html + explicit constexpr AtomicHook(FnPtr default_fn) + : /* hook_(deliberately omitted), */ default_fn_(default_fn) { + static_assert(kUninitialized == 0, "here we rely on zero-initialization"); + } #endif // Stores the provided function pointer as the value for this hook. @@ -159,9 +191,10 @@ class AtomicHook<ReturnType (*)(Args...)> { }; #undef ABSL_HAVE_WORKING_ATOMIC_POINTER +#undef ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT } // namespace base_internal -} // inline namespace lts_2019_08_08 +ABSL_NAMESPACE_END } // namespace absl #endif // ABSL_BASE_INTERNAL_ATOMIC_HOOK_H_ |