diff options
Diffstat (limited to 'absl/base/internal/atomic_hook.h')
| -rw-r--r-- | absl/base/internal/atomic_hook.h | 26 |
1 files changed, 18 insertions, 8 deletions
diff --git a/absl/base/internal/atomic_hook.h b/absl/base/internal/atomic_hook.h index 803e9059761c..09f763d0742b 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_ @@ -23,8 +22,10 @@ #ifdef _MSC_FULL_VER #define ABSL_HAVE_WORKING_ATOMIC_POINTER 0 +#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 0 #else #define ABSL_HAVE_WORKING_ATOMIC_POINTER 1 +#define ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT 1 #endif namespace absl { @@ -33,16 +34,17 @@ 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. +// `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(). +// `ABSL_CONST_INIT 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. @@ -57,12 +59,19 @@ 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 + // On MSVC, this function sometimes executes after dynamic initiazliation =(. + // If a non-zero `hook_` has been installed by a dynamic initializer, we want + // to preserve it. If not, `hook_` will be zero initialized and we have no + // need to set it to `kUninitialized`. + // https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html explicit constexpr AtomicHook(FnPtr default_fn) - : hook_(kUninitialized), default_fn_(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. @@ -158,6 +167,7 @@ class AtomicHook<ReturnType (*)(Args...)> { }; #undef ABSL_HAVE_WORKING_ATOMIC_POINTER +#undef ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT } // namespace base_internal } // namespace absl |