//==- llvm/ADT/IntrusiveRefCntPtr.h - Smart Refcounting Pointer --*- 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 RefCountedBase, ThreadSafeRefCountedBase, and

// IntrusiveRefCntPtr classes.

//

// IntrusiveRefCntPtr is a smart pointer to an object which maintains a

// reference count.  (ThreadSafe)RefCountedBase is a mixin class that adds a

// refcount member variable and methods for updating the refcount.  An object

// that inherits from (ThreadSafe)RefCountedBase deletes itself when its

// refcount hits zero.

//

// For example:

//

//   class MyClass : public RefCountedBase<MyClass> {};

//

//   void foo() {

//     // Constructing an IntrusiveRefCntPtr increases the pointee's refcount by

//     // 1 (from 0 in this case).

//     IntrusiveRefCntPtr<MyClass> Ptr1(new MyClass());

//

//     // Copying an IntrusiveRefCntPtr increases the pointee's refcount by 1.

//     IntrusiveRefCntPtr<MyClass> Ptr2(Ptr1);

//

//     // Constructing an IntrusiveRefCntPtr has no effect on the object's

//     // refcount.  After a move, the moved-from pointer is null.

//     IntrusiveRefCntPtr<MyClass> Ptr3(std::move(Ptr1));

//     assert(Ptr1 == nullptr);

//

//     // Clearing an IntrusiveRefCntPtr decreases the pointee's refcount by 1.

//     Ptr2.reset();

//

//     // The object deletes itself when we return from the function, because

//     // Ptr3's destructor decrements its refcount to 0.

//   }

//

// You can use IntrusiveRefCntPtr with isa<T>(), dyn_cast<T>(), etc.:

//

//   IntrusiveRefCntPtr<MyClass> Ptr(new MyClass());

//   OtherClass *Other = dyn_cast<OtherClass>(Ptr);  // Ptr.get() not required

//

// IntrusiveRefCntPtr works with any class that

//

//  - inherits from (ThreadSafe)RefCountedBase,

//  - has Retain() and Release() methods, or

//  - specializes IntrusiveRefCntPtrInfo.

//

//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_INTRUSIVEREFCNTPTR_H

#define LLVM_ADT_INTRUSIVEREFCNTPTR_H

#include <atomic>

#include <cassert>

#include <cstddef>

namespace llvm {

/// A CRTP mixin class that adds reference counting to a type.

///

/// The lifetime of an object which inherits from RefCountedBase is managed by

/// calls to Release() and Retain(), which increment and decrement the object's

/// refcount, respectively.  When a Release() call decrements the refcount to 0,

/// the object deletes itself.

template <class Derived> class RefCountedBase {

  mutable unsigned RefCount = 0;

public:

  RefCountedBase() = default;

  RefCountedBase(const RefCountedBase &) {}

  void Retain() const { ++RefCount; }

  void Release() const {

    assert(RefCount > 0 && "Reference count is already zero.");

    if (--RefCount == 0)

      delete static_cast<const Derived *>(this);

  }

};

/// A thread-safe version of \c RefCountedBase.

template <class Derived> class ThreadSafeRefCountedBase {

  mutable std::atomic<int> RefCount;

protected:

  ThreadSafeRefCountedBase() : RefCount(0) {}

public:

  void Retain() const { RefCount.fetch_add(1, std::memory_order_relaxed); }

  void Release() const {

    int NewRefCount = RefCount.fetch_sub(1, std::memory_order_acq_rel) - 1;

    assert(NewRefCount >= 0 && "Reference count was already zero.");

    if (NewRefCount == 0)

      delete static_cast<const Derived *>(this);

  }

};

/// Class you can specialize to provide custom retain/release functionality for

/// a type.

///

/// Usually specializing this class is not necessary, as IntrusiveRefCntPtr

/// works with any type which defines Retain() and Release() functions -- you

/// can define those functions yourself if RefCountedBase doesn't work for you.

///

/// One case when you might want to specialize this type is if you have

///  - Foo.h defines type Foo and includes Bar.h, and

///  - Bar.h uses IntrusiveRefCntPtr<Foo> in inline functions.

///

/// Because Foo.h includes Bar.h, Bar.h can't include Foo.h in order to pull in

/// the declaration of Foo.  Without the declaration of Foo, normally Bar.h

/// wouldn't be able to use IntrusiveRefCntPtr<Foo>, which wants to call

/// T::Retain and T::Release.

///

/// To resolve this, Bar.h could include a third header, FooFwd.h, which

/// forward-declares Foo and specializes IntrusiveRefCntPtrInfo<Foo>.  Then

/// Bar.h could use IntrusiveRefCntPtr<Foo>, although it still couldn't call any

/// functions on Foo itself, because Foo would be an incomplete type.

template <typename T> struct IntrusiveRefCntPtrInfo {

  static void retain(T *obj) { obj->Retain(); }

  static void release(T *obj) { obj->Release(); }

};

/// A smart pointer to a reference-counted object that inherits from

/// RefCountedBase or ThreadSafeRefCountedBase.

///

/// This class increments its pointee's reference count when it is created, and

/// decrements its refcount when it's destroyed (or is changed to point to a

/// different object).

template <typename T> class IntrusiveRefCntPtr {

  T *Obj = nullptr;

public:

  using element_type = T;

  explicit IntrusiveRefCntPtr() = default;

  IntrusiveRefCntPtr(T *obj) : Obj(obj) { retain(); }

  IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S) : Obj(S.Obj) { retain(); }

  IntrusiveRefCntPtr(IntrusiveRefCntPtr &&S) : Obj(S.Obj) { S.Obj = nullptr; }

  template <class X>

  IntrusiveRefCntPtr(IntrusiveRefCntPtr<X> &&S) : Obj(S.get()) {

    S.Obj = nullptr;

  }

  template <class X>

  IntrusiveRefCntPtr(const IntrusiveRefCntPtr<X> &S) : Obj(S.get()) {

    retain();

  }

  ~IntrusiveRefCntPtr() { release(); }

  IntrusiveRefCntPtr &operator=(IntrusiveRefCntPtr S) {

    swap(S);

    return *this;

  }

  T &operator*() const { return *Obj; }

  T *operator->() const { return Obj; }

  T *get() const { return Obj; }

  explicit operator bool() const { return Obj; }

  void swap(IntrusiveRefCntPtr &other) {

    T *tmp = other.Obj;

    other.Obj = Obj;

    Obj = tmp;

  }

  void reset() {

    release();

    Obj = nullptr;

  }

  void resetWithoutRelease() { Obj = nullptr; }

private:

  void retain() {

    if (Obj)

      IntrusiveRefCntPtrInfo<T>::retain(Obj);

  }

  void release() {

    if (Obj)

      IntrusiveRefCntPtrInfo<T>::release(Obj);

  }

  template <typename X> friend class IntrusiveRefCntPtr;

};

template <class T, class U>

inline bool operator==(const IntrusiveRefCntPtr<T> &A,

                       const IntrusiveRefCntPtr<U> &B) {

  return A.get() == B.get();

}

template <class T, class U>

inline bool operator!=(const IntrusiveRefCntPtr<T> &A,

                       const IntrusiveRefCntPtr<U> &B) {

  return A.get() != B.get();

}

template <class T, class U>

inline bool operator==(const IntrusiveRefCntPtr<T> &A, U *B) {

  return A.get() == B;

}

template <class T, class U>

inline bool operator!=(const IntrusiveRefCntPtr<T> &A, U *B) {

  return A.get() != B;

}

template <class T, class U>

inline bool operator==(T *A, const IntrusiveRefCntPtr<U> &B) {

  return A == B.get();

}

template <class T, class U>

inline bool operator!=(T *A, const IntrusiveRefCntPtr<U> &B) {

  return A != B.get();

}

template <class T>

bool operator==(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {

  return !B;

}

template <class T>

bool operator==(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {

  return B == A;

}

template <class T>

bool operator!=(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {

  return !(A == B);

}

template <class T>

bool operator!=(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {

  return !(A == B);

}

// Make IntrusiveRefCntPtr work with dyn_cast, isa, and the other idioms from

// Casting.h.

template <typename From> struct simplify_type;

template <class T> struct simplify_type<IntrusiveRefCntPtr<T>> {

  using SimpleType = T *;

  static SimpleType getSimplifiedValue(IntrusiveRefCntPtr<T> &Val) {

    return Val.get();

  }

};

template <class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {

  using SimpleType = /*const*/ T *;

  static SimpleType getSimplifiedValue(const IntrusiveRefCntPtr<T> &Val) {

    return Val.get();

  }

};

} // end namespace llvm

#endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H