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//===-- llvm/Support/ManagedStatic.h - Static Global wrapper ----*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file defines the ManagedStatic class and the llvm_shutdown() function.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_MANAGEDSTATIC_H
#define LLVM_SUPPORT_MANAGEDSTATIC_H
#include <atomic>
#include <cstddef>
namespace llvm {
/// object_creator - Helper method for ManagedStatic.
template <class C> struct object_creator {
static void *call() { return new C(); }
};
/// object_deleter - Helper method for ManagedStatic.
///
template <typename T> struct object_deleter {
static void call(void *Ptr) { delete (T *)Ptr; }
};
template <typename T, size_t N> struct object_deleter<T[N]> {
static void call(void *Ptr) { delete[](T *)Ptr; }
};
// ManagedStatic must be initialized to zero, and it must *not* have a dynamic
// initializer because managed statics are often created while running other
// dynamic initializers. In standard C++11, the best way to accomplish this is
// with a constexpr default constructor. However, different versions of the
// Visual C++ compiler have had bugs where, even though the constructor may be
// constexpr, a dynamic initializer may be emitted depending on optimization
// settings. For the affected versions of MSVC, use the old linker
// initialization pattern of not providing a constructor and leaving the fields
// uninitialized. See http://llvm.org/PR41367 for details.
#if !defined(_MSC_VER) || (_MSC_VER >= 1925) || defined(__clang__)
#define LLVM_USE_CONSTEXPR_CTOR
#endif
/// ManagedStaticBase - Common base class for ManagedStatic instances.
class ManagedStaticBase {
protected:
#ifdef LLVM_USE_CONSTEXPR_CTOR
mutable std::atomic<void *> Ptr{};
mutable void (*DeleterFn)(void *) = nullptr;
mutable const ManagedStaticBase *Next = nullptr;
#else
// This should only be used as a static variable, which guarantees that this
// will be zero initialized.
mutable std::atomic<void *> Ptr;
mutable void (*DeleterFn)(void *);
mutable const ManagedStaticBase *Next;
#endif
void RegisterManagedStatic(void *(*creator)(), void (*deleter)(void*)) const;
public:
#ifdef LLVM_USE_CONSTEXPR_CTOR
constexpr ManagedStaticBase() = default;
#endif
/// isConstructed - Return true if this object has not been created yet.
bool isConstructed() const { return Ptr != nullptr; }
void destroy() const;
};
/// ManagedStatic - This transparently changes the behavior of global statics to
/// be lazily constructed on demand (good for reducing startup times of dynamic
/// libraries that link in LLVM components) and for making destruction be
/// explicit through the llvm_shutdown() function call.
///
template <class C, class Creator = object_creator<C>,
class Deleter = object_deleter<C>>
class ManagedStatic : public ManagedStaticBase {
public:
// Accessors.
C &operator*() {
void *Tmp = Ptr.load(std::memory_order_acquire);
if (!Tmp)
RegisterManagedStatic(Creator::call, Deleter::call);
return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
}
C *operator->() { return &**this; }
const C &operator*() const {
void *Tmp = Ptr.load(std::memory_order_acquire);
if (!Tmp)
RegisterManagedStatic(Creator::call, Deleter::call);
return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
}
const C *operator->() const { return &**this; }
// Extract the instance, leaving the ManagedStatic uninitialized. The
// user is then responsible for the lifetime of the returned instance.
C *claim() {
return static_cast<C *>(Ptr.exchange(nullptr));
}
};
/// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
void llvm_shutdown();
/// llvm_shutdown_obj - This is a simple helper class that calls
/// llvm_shutdown() when it is destroyed.
struct llvm_shutdown_obj {
llvm_shutdown_obj() = default;
~llvm_shutdown_obj() { llvm_shutdown(); }
};
} // end namespace llvm
#endif // LLVM_SUPPORT_MANAGEDSTATIC_H
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