LLVM  9.0.0svn
ManagedStatic.h
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1 //===-- llvm/Support/ManagedStatic.h - Static Global wrapper ----*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines the ManagedStatic class and the llvm_shutdown() function.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_SUPPORT_MANAGEDSTATIC_H
14 #define LLVM_SUPPORT_MANAGEDSTATIC_H
15 
16 #include <atomic>
17 #include <cstddef>
18 
19 namespace llvm {
20 
21 /// object_creator - Helper method for ManagedStatic.
22 template <class C> struct object_creator {
23  static void *call() { return new C(); }
24 };
25 
26 /// object_deleter - Helper method for ManagedStatic.
27 ///
28 template <typename T> struct object_deleter {
29  static void call(void *Ptr) { delete (T *)Ptr; }
30 };
31 template <typename T, size_t N> struct object_deleter<T[N]> {
32  static void call(void *Ptr) { delete[](T *)Ptr; }
33 };
34 
35 /// ManagedStaticBase - Common base class for ManagedStatic instances.
37 protected:
38  // This should only be used as a static variable, which guarantees that this
39  // will be zero initialized.
40  mutable std::atomic<void *> Ptr;
41  mutable void (*DeleterFn)(void*);
42  mutable const ManagedStaticBase *Next;
43 
44  void RegisterManagedStatic(void *(*creator)(), void (*deleter)(void*)) const;
45 
46 public:
47  /// isConstructed - Return true if this object has not been created yet.
48  bool isConstructed() const { return Ptr != nullptr; }
49 
50  void destroy() const;
51 };
52 
53 /// ManagedStatic - This transparently changes the behavior of global statics to
54 /// be lazily constructed on demand (good for reducing startup times of dynamic
55 /// libraries that link in LLVM components) and for making destruction be
56 /// explicit through the llvm_shutdown() function call.
57 ///
58 template <class C, class Creator = object_creator<C>,
59  class Deleter = object_deleter<C>>
61 public:
62  // Accessors.
63  C &operator*() {
64  void *Tmp = Ptr.load(std::memory_order_acquire);
65  if (!Tmp)
66  RegisterManagedStatic(Creator::call, Deleter::call);
67 
68  return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
69  }
70 
71  C *operator->() { return &**this; }
72 
73  const C &operator*() const {
74  void *Tmp = Ptr.load(std::memory_order_acquire);
75  if (!Tmp)
76  RegisterManagedStatic(Creator::call, Deleter::call);
77 
78  return *static_cast<C *>(Ptr.load(std::memory_order_relaxed));
79  }
80 
81  const C *operator->() const { return &**this; }
82 };
83 
84 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
85 void llvm_shutdown();
86 
87 /// llvm_shutdown_obj - This is a simple helper class that calls
88 /// llvm_shutdown() when it is destroyed.
90  llvm_shutdown_obj() = default;
92 };
93 
94 } // end namespace llvm
95 
96 #endif // LLVM_SUPPORT_MANAGEDSTATIC_H
uint64_t CallInst * C
This class represents lattice values for constants.
Definition: AllocatorList.h:23
const ManagedStaticBase * Next
Definition: ManagedStatic.h:42
static void call(void *Ptr)
Definition: ManagedStatic.h:29
object_deleter - Helper method for ManagedStatic.
Definition: ManagedStatic.h:28
void llvm_shutdown()
llvm_shutdown - Deallocate and destroy all ManagedStatic variables.
static void * call()
Definition: ManagedStatic.h:23
const C & operator*() const
Definition: ManagedStatic.h:73
std::atomic< void * > Ptr
Definition: ManagedStatic.h:40
const C * operator->() const
Definition: ManagedStatic.h:81
ManagedStaticBase - Common base class for ManagedStatic instances.
Definition: ManagedStatic.h:36
bool isConstructed() const
isConstructed - Return true if this object has not been created yet.
Definition: ManagedStatic.h:48
static void call(void *Ptr)
Definition: ManagedStatic.h:32
llvm_shutdown_obj - This is a simple helper class that calls llvm_shutdown() when it is destroyed...
Definition: ManagedStatic.h:89
#define N
ManagedStatic - This transparently changes the behavior of global statics to be lazily constructed on...
Definition: ManagedStatic.h:60
void deleter(T *Ptr)
Definition: STLExtras.h:153
object_creator - Helper method for ManagedStatic.
Definition: ManagedStatic.h:22