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Export of internal Abseil changes

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3e60f355db5afd7a864591d81a6c383b6c0a0780 by Samuel Benzaquen <sbenza@google.com>:

Internal change

PiperOrigin-RevId: 272531442

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6d189240b8cebe3a390c730de491156d03049229 by Andy Getzendanner <durandal@google.com>:

Fix AtomicHook init-order fiasco under MSVC 2019.

On this platform, constexpr static init sometimes happens after dynamic init =/.  When it does, we should not zero hook_ (overwriting the value written there by dynamic init); instead we should leave it alone.  This works even when constexpr static init goes first since all uses of AtomicHook should have static storage duration and be zero-initialized.

https://developercommunity.visualstudio.com/content/problem/336946/class-with-constexpr-constructor-not-using-static.html

PiperOrigin-RevId: 272525226

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d01b14fc06bc75b41c51976ed32e7c304ea1aab7 by Abseil Team <absl-team@google.com>:

exclude emscripten from running tests involving long doubles

PiperOrigin-RevId: 272497628
GitOrigin-RevId: 3e60f355db5afd7a864591d81a6c383b6c0a0780
Change-Id: I3c8a8f5acaf7652a06ef40cf028ef5d2e142f81b
This commit is contained in:
Abseil Team 2019-10-02 15:20:57 -07:00 • committed by CJ Johnson
parent aad33fefaa
commit 25597bdfc1
12 changed files with 166 additions and 12 deletions
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26
absl/base/internal/atomic_hook.h
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@ -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