LLVM  4.0.0
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;
76  RefCountedBase(const RefCountedBase &) : RefCount(0) {}
77 
78  void Retain() const { ++RefCount; }
79  void Release() const {
80  assert(RefCount > 0 && "Reference count is already zero.");
81  if (--RefCount == 0)
82  delete static_cast<const Derived *>(this);
83  }
84 };
85 
86 /// A thread-safe version of \c RefCountedBase.
87 template <class Derived> class ThreadSafeRefCountedBase {
88  mutable std::atomic<int> RefCount;
89 
90 protected:
91  ThreadSafeRefCountedBase() : RefCount(0) {}
92 
93 public:
94  void Retain() const { RefCount.fetch_add(1, std::memory_order_relaxed); }
95 
96  void Release() const {
97  int NewRefCount = RefCount.fetch_sub(1, std::memory_order_acq_rel) - 1;
98  assert(NewRefCount >= 0 && "Reference count was already zero.");
99  if (NewRefCount == 0)
100  delete static_cast<const Derived *>(this);
101  }
102 };
103 
104 /// Class you can specialize to provide custom retain/release functionality for
105 /// a type.
106 ///
107 /// Usually specializing this class is not necessary, as IntrusiveRefCntPtr
108 /// works with any type which defines Retain() and Release() functions -- you
109 /// can define those functions yourself if RefCountedBase doesn't work for you.
110 ///
111 /// One case when you might want to specialize this type is if you have
112 /// - Foo.h defines type Foo and includes Bar.h, and
113 /// - Bar.h uses IntrusiveRefCntPtr<Foo> in inline functions.
114 ///
115 /// Because Foo.h includes Bar.h, Bar.h can't include Foo.h in order to pull in
116 /// the declaration of Foo. Without the declaration of Foo, normally Bar.h
117 /// wouldn't be able to use IntrusiveRefCntPtr<Foo>, which wants to call
118 /// T::Retain and T::Release.
119 ///
120 /// To resolve this, Bar.h could include a third header, FooFwd.h, which
121 /// forward-declares Foo and specializes IntrusiveRefCntPtrInfo<Foo>. Then
122 /// Bar.h could use IntrusiveRefCntPtr<Foo>, although it still couldn't call any
123 /// functions on Foo itself, because Foo would be an incomplete type.
124 template <typename T> struct IntrusiveRefCntPtrInfo {
125  static void retain(T *obj) { obj->Retain(); }
126  static void release(T *obj) { obj->Release(); }
127 };
128 
129 /// A smart pointer to a reference-counted object that inherits from
130 /// RefCountedBase or ThreadSafeRefCountedBase.
131 ///
132 /// This class increments its pointee's reference count when it is created, and
133 /// decrements its refcount when it's destroyed (or is changed to point to a
134 /// different object).
135 template <typename T> class IntrusiveRefCntPtr {
136  T *Obj = nullptr;
137 
138 public:
139  typedef T element_type;
140 
141  explicit IntrusiveRefCntPtr() = default;
142  IntrusiveRefCntPtr(T *obj) : Obj(obj) { retain(); }
143  IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S) : Obj(S.Obj) { retain(); }
144  IntrusiveRefCntPtr(IntrusiveRefCntPtr &&S) : Obj(S.Obj) { S.Obj = nullptr; }
145 
146  template <class X>
148  S.Obj = nullptr;
149  }
150 
151  template <class X>
153  retain();
154  }
155 
157  swap(S);
158  return *this;
159  }
160 
161  ~IntrusiveRefCntPtr() { release(); }
162 
163  T &operator*() const { return *Obj; }
164  T *operator->() const { return Obj; }
165  T *get() const { return Obj; }
166  explicit operator bool() const { return Obj; }
167 
168  void swap(IntrusiveRefCntPtr &other) {
169  T *tmp = other.Obj;
170  other.Obj = Obj;
171  Obj = tmp;
172  }
173 
174  void reset() {
175  release();
176  Obj = nullptr;
177  }
178 
179  void resetWithoutRelease() { Obj = nullptr; }
180 
181 private:
182  void retain() {
183  if (Obj)
185  }
186  void release() {
187  if (Obj)
189  }
190 
191  template <typename X> friend class IntrusiveRefCntPtr;
192 };
193 
194 template <class T, class U>
195 inline bool operator==(const IntrusiveRefCntPtr<T> &A,
196  const IntrusiveRefCntPtr<U> &B) {
197  return A.get() == B.get();
198 }
199 
200 template <class T, class U>
201 inline bool operator!=(const IntrusiveRefCntPtr<T> &A,
202  const IntrusiveRefCntPtr<U> &B) {
203  return A.get() != B.get();
204 }
205 
206 template <class T, class U>
207 inline bool operator==(const IntrusiveRefCntPtr<T> &A, U *B) {
208  return A.get() == B;
209 }
210 
211 template <class T, class U>
212 inline bool operator!=(const IntrusiveRefCntPtr<T> &A, U *B) {
213  return A.get() != B;
214 }
215 
216 template <class T, class U>
217 inline bool operator==(T *A, const IntrusiveRefCntPtr<U> &B) {
218  return A == B.get();
219 }
220 
221 template <class T, class U>
222 inline bool operator!=(T *A, const IntrusiveRefCntPtr<U> &B) {
223  return A != B.get();
224 }
225 
226 template <class T>
227 bool operator==(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
228  return !B;
229 }
230 
231 template <class T>
232 bool operator==(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
233  return B == A;
234 }
235 
236 template <class T>
237 bool operator!=(std::nullptr_t A, const IntrusiveRefCntPtr<T> &B) {
238  return !(A == B);
239 }
240 
241 template <class T>
242 bool operator!=(const IntrusiveRefCntPtr<T> &A, std::nullptr_t B) {
243  return !(A == B);
244 }
245 
246 // Make IntrusiveRefCntPtr work with dyn_cast, isa, and the other idioms from
247 // Casting.h.
248 template <typename From> struct simplify_type;
249 
250 template <class T> struct simplify_type<IntrusiveRefCntPtr<T>> {
251  typedef T *SimpleType;
253  return Val.get();
254  }
255 };
256 
257 template <class T> struct simplify_type<const IntrusiveRefCntPtr<T>> {
258  typedef /*const*/ T *SimpleType;
260  return Val.get();
261  }
262 };
263 
264 } // end namespace llvm
265 
266 #endif // LLVM_ADT_INTRUSIVEREFCNTPTR_H
static SimpleType getSimplifiedValue(const IntrusiveRefCntPtr< T > &Val)
Class you can specialize to provide custom retain/release functionality for a type.
A CRTP mixin class that adds reference counting to a type.
RefCountedBase(const RefCountedBase &)
static GCRegistry::Add< OcamlGC > B("ocaml","ocaml 3.10-compatible GC")
RefCountedBase()=default
A smart pointer to a reference-counted object that inherits from RefCountedBase or ThreadSafeRefCount...
A thread-safe version of RefCountedBase.
IntrusiveRefCntPtr(const IntrusiveRefCntPtr &S)
bool operator!=(uint64_t V1, const APInt &V2)
Definition: APInt.h:1724
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:1722
IntrusiveRefCntPtr & operator=(IntrusiveRefCntPtr S)
static GCRegistry::Add< ErlangGC > A("erlang","erlang-compatible garbage collector")
IntrusiveRefCntPtr(IntrusiveRefCntPtr< X > &&S)