mirror of
https://github.com/mozilla/gecko-dev.git
synced 2024-11-23 04:41:11 +00:00
67 lines
2.4 KiB
C++
67 lines
2.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
|
|
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
|
|
/* This Source Code Form is subject to the terms of the Mozilla Public
|
|
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
|
|
* You can obtain one at http://mozilla.org/MPL/2.0/. */
|
|
|
|
#ifndef mozilla_NeverDestroyed_h
|
|
#define mozilla_NeverDestroyed_h
|
|
|
|
#include <new>
|
|
#include <type_traits>
|
|
#include <utility>
|
|
#include "mozilla/Attributes.h"
|
|
|
|
namespace mozilla {
|
|
|
|
// Helper type for creating a local static member of type `T` when `T` has a
|
|
// non-trivial static destructor. When used for the local static value, this
|
|
// type will avoid introducing a static destructor for these types, as they
|
|
// will survive until shutdown.
|
|
//
|
|
// This can be very useful to avoid static destructors, which are heavily
|
|
// discouraged. Using this type is unnecessary if `T` already has a trivial
|
|
// destructor, and may introduce unnecessary extra overhead.
|
|
//
|
|
// This type must only be used with static local members within a function,
|
|
// which will be enforced by the clang static analysis.
|
|
template <typename T>
|
|
class MOZ_STATIC_LOCAL_CLASS MOZ_INHERIT_TYPE_ANNOTATIONS_FROM_TEMPLATE_ARGS
|
|
NeverDestroyed {
|
|
public:
|
|
static_assert(
|
|
!std::is_trivially_destructible_v<T>,
|
|
"NeverDestroyed is unnecessary for trivially destructable types");
|
|
|
|
// Allow constructing the inner type.
|
|
// This isn't constexpr, as it requires invoking placement-new. See the
|
|
// comment on `mStorage`.
|
|
template <typename... U>
|
|
explicit NeverDestroyed(U&&... aArgs) {
|
|
new (mStorage) T(std::forward<U>(aArgs)...);
|
|
}
|
|
|
|
const T& operator*() const { return *get(); }
|
|
T& operator*() { return *get(); }
|
|
|
|
const T* operator->() const { return get(); }
|
|
T* operator->() { return get(); }
|
|
|
|
const T* get() const { return reinterpret_cast<T*>(mStorage); }
|
|
T* get() { return reinterpret_cast<T*>(mStorage); }
|
|
|
|
// Block copy & move constructor, as the type is not safe to copy.
|
|
NeverDestroyed(const NeverDestroyed&) = delete;
|
|
NeverDestroyed& operator=(const NeverDestroyed&) = delete;
|
|
|
|
private:
|
|
// Correctly aligned storage for the type. We unfortunately can't use a union
|
|
// for alignment & constexpr initialization as that would require an explicit
|
|
// destructor declaration, making `NeverDestroyed` non-trivially destructable.
|
|
alignas(T) char mStorage[sizeof(T)];
|
|
};
|
|
|
|
}; // namespace mozilla
|
|
|
|
#endif // mozilla_NeverDestroyed_h
|