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IntrusiveRefCntPtr.h
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1 //==- llvm/ADT/IntrusiveRefCntPtr.h - Smart Refcounting Pointer --*- C++ -*-==//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines the RefCountedBase, ThreadSafeRefCountedBase, and
11 // IntrusiveRefCntPtr classes.
12 //
13 // IntrusiveRefCntPtr is a smart pointer to an object which maintains a
14 // reference count. (ThreadSafe)RefCountedBase is a mixin class that adds a
15 // refcount member variable and methods for updating the refcount. An object
16 // that inherits from (ThreadSafe)RefCountedBase deletes itself when its
17 // refcount hits zero.
18 //
19 // For example:
20 //
21 // class MyClass : public RefCountedBase<MyClass> {};
22 //
23 // void foo() {
24 // // Constructing an IntrusiveRefCntPtr increases the pointee's refcount by
25 // // 1 (from 0 in this case).
26 // IntrusiveRefCntPtr<MyClass> Ptr1(new MyClass());
27 //
28 // // Copying an IntrusiveRefCntPtr increases the pointee's refcount by 1.
29 // IntrusiveRefCntPtr<MyClass> Ptr2(Ptr1);
30 //
31 // // Constructing an IntrusiveRefCntPtr has no effect on the object's
32 // // refcount. After a move, the moved-from pointer is null.
33 // IntrusiveRefCntPtr<MyClass> Ptr3(std::move(Ptr1));
34 // assert(Ptr1 == nullptr);
35 //
36 // // Clearing an IntrusiveRefCntPtr decreases the pointee's refcount by 1.
37 // Ptr2.reset();
38 //
39 // // The object deletes itself when we return from the function, because
40 // // Ptr3's destructor decrements its refcount to 0.
41 // }
42 //
43 // You can use IntrusiveRefCntPtr with isa<T>(), dyn_cast<T>(), etc.:
44 //
45 // IntrusiveRefCntPtr<MyClass> Ptr(new MyClass());
46 // OtherClass *Other = dyn_cast<OtherClass>(Ptr); // Ptr.get() not required
47 //
48 // IntrusiveRefCntPtr works with any class that
49 //
50 // - inherits from (ThreadSafe)RefCountedBase,
51 // - has Retain() and Release() methods, or
52 // - specializes IntrusiveRefCntPtrInfo.
53 //
54 //===----------------------------------------------------------------------===//
55 
56 #ifndef LLVM_ADT_INTRUSIVEREFCNTPTR_H
57 #define LLVM_ADT_INTRUSIVEREFCNTPTR_H
58 
59 #include <atomic>
60 #include <cassert>
61 #include <cstddef>
62 
63 namespace llvm {
64 
65 /// A CRTP mixin class that adds reference counting to a type.
66 ///
67 /// The lifetime of an object which inherits from RefCountedBase is managed by
68 /// calls to Release() and Retain(), which increment and decrement the object's
69 /// refcount, respectively. When a Release() call decrements the refcount to 0,
70 /// the object deletes itself.
71 template <class Derived> class RefCountedBase {
72  mutable unsigned RefCount = 0;
73 
74 public:
75  RefCountedBase() = default;
77 
78  void Retain() const { ++RefCount; }
79 
80  void Release() const {
81  assert(RefCount > 0 && "Reference count is already zero.");
82  if (--RefCount == 0)
83  delete static_cast<const Derived *>(this);
84  }
85 };
86 
87 /// A thread-safe version of \c RefCountedBase.
88 template <class Derived> class ThreadSafeRefCountedBase {
89  mutable std::atomic<int> RefCount;
90 
91 protected:
92  ThreadSafeRefCountedBase() : RefCount(0) {}
93 
94 public:
95  void Retain() const { RefCount.fetch_add(1, std::memory_order_relaxed); }
96 
97  void Release() const {
98  int NewRefCount = RefCount.fetch_sub(1, std::memory_order_acq_rel) - 1;
99  assert(NewRefCount >= 0 && "Reference count was already zero.");
100  if (NewRefCount == 0)
101  delete static_cast<const Derived *>(this);
102  }
103 };
104 
105 /// Class you can specialize to provide custom retain/release functionality for
106 /// a type.
107 ///
108 /// Usually specializing this class is not necessary, as IntrusiveRefCntPtr
109 /// works with any type which defines Retain() and Release() functions -- you
110 /// can define those functions yourself if RefCountedBase doesn't work for you.
111 ///
112 /// One case when you might want to specialize this type is if you have
113 /// - Foo.h defines type Foo and includes Bar.h, and
114 /// - Bar.h uses IntrusiveRefCntPtr<Foo> in inline functions.
115 ///
116 /// Because Foo.h includes Bar.h, Bar.h can't include Foo.h in order to pull in
117 /// the declaration of Foo. Without the declaration of Foo, normally Bar.h
118 /// wouldn't be able to use IntrusiveRefCntPtr<Foo>, which wants to call
119 /// T::Retain and T::Release.
120 ///
121 /// To resolve this, Bar.h could include a third header, FooFwd.h, which
122 /// forward-declares Foo and specializes IntrusiveRefCntPtrInfo<Foo>. Then
123 /// Bar.h could use IntrusiveRefCntPtr<Foo>, although it still couldn't call any
124 /// functions on Foo itself, because Foo would be an incomplete type.
125 template <typename T> struct IntrusiveRefCntPtrInfo {
126  static void retain(T *obj) { obj->Retain(); }
127  static void release(T *obj) { obj->Release(); }
128 };
129 
130 /// A smart pointer to a reference-counted object that inherits from
131 /// RefCountedBase or ThreadSafeRefCountedBase.
132 ///
133 /// This class increments its pointee's reference count when it is created, and
134 /// decrements its refcount when it's destroyed (or is changed to point to a
135 /// different object).
136 template <typename T> class IntrusiveRefCntPtr {
137  T *Obj = nullptr;
138 
139 public:
140  using element_type = T;
141 
142  explicit IntrusiveRefCntPtr() = default;
143  IntrusiveRefCntPtr(T *obj) : Obj(obj) { retain(); }
144  IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S) : Obj(S.Obj) { retain(); }
145  IntrusiveRefCntPtr(IntrusiveRefCntPtr &&S) : Obj(S.Obj) { S.Obj = nullptr; }
146 
147  template <class X>
149  S.Obj = nullptr;
150  }
151 
152  template <class X>
153  IntrusiveRefCntPtr(const IntrusiveRefCntPtr<X> &S) : Obj(S.get()) {
154  retain();
155  }
156 
158 
160  swap(S);
161  return *this;
162  }
163 
164  T &operator*() const { return *Obj; }
165  T *operator->() const { return Obj; }
166  T *get() const { return Obj; }
167  explicit operator bool() const { return Obj; }
168 
169  void swap(IntrusiveRefCntPtr &other) {
170  T *tmp = other.Obj;
171  other.Obj = Obj;
172  Obj = tmp;
173  }
174 
175  void reset() {
176  release();
177  Obj = nullptr;
178  }
179 
180  void resetWithoutRelease() { Obj = nullptr; }
181 
182 private:
183  void retain() {
184  if (Obj)
186  }
187 
188  void release() {
189  if (Obj)
191  }
192 
193  template <typename X> friend class IntrusiveRefCntPtr;
194 };
195 
196 template <class T, class U>
197 inline bool operator==(const IntrusiveRefCntPtr<T> &A,
198  const IntrusiveRefCntPtr<U> &B) {
199  return A.get() == B.get();
200 }
201 
202 template <class T, class U>
203 inline bool operator!=(const IntrusiveRefCntPtr<T> &A,
204  const IntrusiveRefCntPtr<U> &B) {
205  return A.get() != B.get();
206 }
207 
208 template <class T, class U>
209 inline bool operator==(const IntrusiveRefCntPtr<T> &A, U *B) {
210  return A.get() == B;
211 }
212 
213 template <class T, class U>
214 inline bool operator!=(const IntrusiveRefCntPtr<T> &A, U *B) {
215  return A.get() != B;
216 }
217 
218 template <class T, class U>
219 inline bool operator==(T *A, const IntrusiveRefCntPtr<U> &B) {
220  return A == B.get();
221 }
222 
223 template <class T, class U>
224 inline bool operator!=(T *A, const IntrusiveRefCntPtr<U> &B) {
225  return A != B.get();
226 }
227 
228 template <class T>
229 bool operator==(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
230  return !B;
231 }
232 
233 template <class T>
234 bool operator==(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
235  return B == A;
236 }
237 
238 template <class T>
239 bool operator!=(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
240  return !(A == B);
241 }
242 
243 template <class T>
244 bool operator!=(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
245  return !(A == B);
246 }
247 
248 // Make IntrusiveRefCntPtr work with dyn_cast, isa, and the other idioms from
249 // Casting.h.
250 template <typename From> struct simplify_type;
251 
252 template <class T> struct simplify_type<IntrusiveRefCntPtr<T>> {
253  using SimpleType = T *;
254 
256  return Val.get();
257  }
258 };
259 
260 template <class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {
261  using SimpleType = /*const*/ T *;
262 
264  return Val.get();
265  }
266 };
267 
268 } // end namespace llvm
269 
270 #endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H
static SimpleType getSimplifiedValue(const IntrusiveRefCntPtr< T > &Val)
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
Class you can specialize to provide custom retain/release functionality for a type.
A CRTP mixin class that adds reference counting to a type.
#define T
RefCountedBase(const RefCountedBase &)
RefCountedBase()=default
#define A
Definition: LargeTest.cpp:12
A smart pointer to a reference-counted object that inherits from RefCountedBase or ThreadSafeRefCount...
#define B
Definition: LargeTest.cpp:24
void swap(llvm::BitVector &LHS, llvm::BitVector &RHS)
Implement std::swap in terms of BitVector swap.
Definition: BitVector.h:923
A thread-safe version of RefCountedBase.
IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S)
bool operator!=(uint64_t V1, const APInt &V2)
Definition: APInt.h:1948
void swap(IntrusiveRefCntPtr &other)
static SimpleType getSimplifiedValue(IntrusiveRefCntPtr< T > &Val)
IntrusiveRefCntPtr(const IntrusiveRefCntPtr< X > &S)
IntrusiveRefCntPtr(IntrusiveRefCntPtr &&S)
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
aarch64 promote const
bool operator==(uint64_t V1, const APInt &V2)
Definition: APInt.h:1946
IntrusiveRefCntPtr & operator=(IntrusiveRefCntPtr S)
IntrusiveRefCntPtr(IntrusiveRefCntPtr< X > &&S)