mirror of
https://github.com/apple/swift.git
synced 2025-12-14 20:36:38 +01:00
88 lines
2.4 KiB
C++
88 lines
2.4 KiB
C++
//===--- Lazy.h - A lazily-initialized object -------------------*- C++ -*-===//
|
|
//
|
|
// This source file is part of the Swift.org open source project
|
|
//
|
|
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
|
|
// Licensed under Apache License v2.0 with Runtime Library Exception
|
|
//
|
|
// See https://swift.org/LICENSE.txt for license information
|
|
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef SWIFT_BASIC_LAZY_H
|
|
#define SWIFT_BASIC_LAZY_H
|
|
|
|
#include <memory>
|
|
|
|
#include "swift/Basic/Malloc.h"
|
|
#include "swift/Basic/type_traits.h"
|
|
#include "swift/Threading/Once.h"
|
|
|
|
namespace swift {
|
|
|
|
/// A template for lazily-constructed, zero-initialized, leaked-on-exit
|
|
/// global objects.
|
|
template <class T> class Lazy {
|
|
alignas(T) char Value[sizeof(T)] = { 0 };
|
|
|
|
swift::once_t OnceToken = {};
|
|
|
|
static void defaultInitCallback(void *ValueAddr) {
|
|
::new (ValueAddr) T();
|
|
}
|
|
|
|
public:
|
|
using Type = T;
|
|
|
|
T &get(void (*initCallback)(void *) = defaultInitCallback);
|
|
|
|
template<typename Arg1>
|
|
T &getWithInit(Arg1 &&arg1);
|
|
|
|
/// Get the value, assuming it must have already been initialized by this
|
|
/// point.
|
|
T &unsafeGetAlreadyInitialized() { return *reinterpret_cast<T *>(&Value); }
|
|
|
|
constexpr Lazy() = default;
|
|
|
|
T *operator->() { return &get(); }
|
|
T &operator*() { return get(); }
|
|
|
|
private:
|
|
Lazy(const Lazy &) = delete;
|
|
Lazy &operator=(const Lazy &) = delete;
|
|
};
|
|
|
|
template <typename T> inline T &Lazy<T>::get(void (*initCallback)(void*)) {
|
|
swift::once(OnceToken, initCallback, &Value);
|
|
return unsafeGetAlreadyInitialized();
|
|
}
|
|
|
|
template <typename T>
|
|
template <typename Arg1> inline T &Lazy<T>::getWithInit(Arg1 &&arg1) {
|
|
struct Data {
|
|
void *address;
|
|
Arg1 &&arg1;
|
|
|
|
static void init(void *context) {
|
|
Data *data = static_cast<Data *>(context);
|
|
::new (data->address) T(static_cast<Arg1&&>(data->arg1));
|
|
}
|
|
} data{&Value, static_cast<Arg1&&>(arg1)};
|
|
|
|
swift::once(OnceToken, &Data::init, &data);
|
|
return unsafeGetAlreadyInitialized();
|
|
}
|
|
|
|
} // end namespace swift
|
|
|
|
#define SWIFT_LAZY_CONSTANT(INITIAL_VALUE) \
|
|
([]{ \
|
|
using T = ::std::remove_reference<decltype(INITIAL_VALUE)>::type; \
|
|
static ::swift::Lazy<T> TheLazy; \
|
|
return TheLazy.get([](void *ValueAddr){ ::new(ValueAddr) T{INITIAL_VALUE}; });\
|
|
}())
|
|
|
|
#endif // SWIFT_BASIC_LAZY_H
|