diff options
Diffstat (limited to 'absl/base/internal/atomic_hook.h')
| -rw-r--r-- | absl/base/internal/atomic_hook.h | 39 |
1 files changed, 30 insertions, 9 deletions
diff --git a/absl/base/internal/atomic_hook.h b/absl/base/internal/atomic_hook.h index d885bc05..ae21cd7f 100644 --- a/absl/base/internal/atomic_hook.h +++ b/absl/base/internal/atomic_hook.h @@ -20,16 +20,21 @@ #include <cstdint> #include <utility> +#include "absl/base/attributes.h" #include "absl/base/config.h" -#ifdef _MSC_FULL_VER -#define ABSL_HAVE_WORKING_ATOMIC_POINTER 0 +#if defined(_MSC_VER) && !defined(__clang__) #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 +#if defined(_MSC_VER) +#define ABSL_HAVE_WORKING_ATOMIC_POINTER 0 +#else +#define ABSL_HAVE_WORKING_ATOMIC_POINTER 1 +#endif + namespace absl { ABSL_NAMESPACE_BEGIN namespace base_internal { @@ -37,6 +42,15 @@ namespace base_internal { template <typename T> class AtomicHook; +// 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 @@ -45,8 +59,11 @@ class AtomicHook; // 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);` +// 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 @@ -65,11 +82,15 @@ class AtomicHook<ReturnType (*)(Args...)> { #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) {} +#elif ABSL_HAVE_WORKING_CONSTEXPR_STATIC_INIT + explicit constexpr AtomicHook(FnPtr default_fn) + : hook_(kUninitialized), default_fn_(default_fn) {} #else - // On MSVC, this function sometimes executes after dynamic initialization =(. - // 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`. + // 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) { |