//== llvm/ADT/IntrusiveRefCntPtr.h - Smart Refcounting Pointer ---*- C++ -*-==//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines IntrusiveRefCntPtr, a template class that
// implements a "smart" pointer for objects that maintain their own
// internal reference count, and RefCountedBase/RefCountedBaseVPTR, two
// generic base classes for objects that wish to have their lifetimes
// managed using reference counting.
//
// IntrusiveRefCntPtr is similar to Boost's intrusive_ptr with added
// LLVM-style casting.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_ADT_INTRUSIVEREFCNTPTR_H
#define LLVM_ADT_INTRUSIVEREFCNTPTR_H
#include <atomic>
#include <cassert>
#include <cstddef>
namespace llvm {
//===----------------------------------------------------------------------===//
/// RefCountedBase - A generic base class for objects that wish to
/// have their lifetimes managed using reference counts. Classes
/// subclass RefCountedBase to obtain such functionality, and are
/// typically handled with IntrusiveRefCntPtr "smart pointers" (see below)
/// which automatically handle the management of reference counts.
/// Objects that subclass RefCountedBase should not be allocated on
/// the stack, as invoking "delete" (which is called when the
/// reference count hits 0) on such objects is an error.
//===----------------------------------------------------------------------===//
template <class Derived>
class RefCountedBase {
mutable unsigned ref_cnt = 0;
public:
RefCountedBase() = default;
RefCountedBase(const RefCountedBase &) : ref_cnt(0) {}
void Retain() const { ++ref_cnt; }
void Release() const {
assert (ref_cnt > 0 && "Reference count is already zero.");
if (--ref_cnt == 0) delete static_cast<const Derived*>(this);
}
};
//===----------------------------------------------------------------------===//
/// RefCountedBaseVPTR - A class that has the same function as
/// RefCountedBase, but with a virtual destructor. Should be used
/// instead of RefCountedBase for classes that already have virtual
/// methods to enforce dynamic allocation via 'new'. Classes that
/// inherit from RefCountedBaseVPTR can't be allocated on stack -
/// attempting to do this will produce a compile error.
//===----------------------------------------------------------------------===//
class RefCountedBaseVPTR {
mutable unsigned ref_cnt = 0;
virtual void anchor();
protected:
RefCountedBaseVPTR() = default;
RefCountedBaseVPTR(const RefCountedBaseVPTR &) : ref_cnt(0) {}
virtual ~RefCountedBaseVPTR() = default;
void Retain() const { ++ref_cnt; }
void Release() const {
assert (ref_cnt > 0 && "Reference count is already zero.");
if (--ref_cnt == 0) delete this;
}
template <typename T>
friend struct IntrusiveRefCntPtrInfo;
};
template <typename T> struct IntrusiveRefCntPtrInfo {
static void retain(T *obj) { obj->Retain(); }
static void release(T *obj) { obj->Release(); }
};
/// \brief A thread-safe version of \c llvm::RefCountedBase.
///
/// A generic base class for objects that wish to have their lifetimes managed
/// using reference counts. Classes subclass \c ThreadSafeRefCountedBase to
/// obtain such functionality, and are typically handled with
/// \c IntrusiveRefCntPtr "smart pointers" which automatically handle the
/// management of reference counts.
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);
}
};
//===----------------------------------------------------------------------===//
/// IntrusiveRefCntPtr - A template class that implements a "smart pointer"
/// that assumes the wrapped object has a reference count associated
/// with it that can be managed via calls to
/// IntrusivePtrAddRef/IntrusivePtrRelease. The smart pointers
/// manage reference counts via the RAII idiom: upon creation of
/// smart pointer the reference count of the wrapped object is
/// incremented and upon destruction of the smart pointer the
/// reference count is decremented. This class also safely handles
/// wrapping NULL pointers.
///
/// Reference counting is implemented via calls to
/// Obj->Retain()/Obj->Release(). Release() is required to destroy
/// the object when the reference count reaches zero. Inheriting from
/// RefCountedBase/RefCountedBaseVPTR takes care of this
/// automatically.
//===----------------------------------------------------------------------===//
template <typename T>
class IntrusiveRefCntPtr {
T* Obj = nullptr;
public:
typedef T element_type;
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& operator=(IntrusiveRefCntPtr S) {
swap(S);
return *this;
}
~IntrusiveRefCntPtr() { release(); }
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);
}
//===----------------------------------------------------------------------===//
// LLVM-style downcasting support for IntrusiveRefCntPtr objects
//===----------------------------------------------------------------------===//
template <typename From> struct simplify_type;
template<class T> struct simplify_type<IntrusiveRefCntPtr<T>> {
typedef T* SimpleType;
static SimpleType getSimplifiedValue(IntrusiveRefCntPtr<T>& Val) {
return Val.get();
}
};
template<class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {
typedef /*const*/ T* SimpleType;
static SimpleType getSimplifiedValue(const IntrusiveRefCntPtr<T>& Val) {
return Val.get();
}
};
} // end namespace llvm
#endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H