1 //===-- llvm/Support/ManagedStatic.h - Static Global wrapper ----*- 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 ManagedStatic class and the llvm_shutdown() function. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_SUPPORT_MANAGEDSTATIC_H 15 #define LLVM_SUPPORT_MANAGEDSTATIC_H 16 17 #include "llvm/Support/Compiler.h" 18 #include <atomic> 19 #include <cstddef> 20 21 namespace llvm { 22 23 /// object_creator - Helper method for ManagedStatic. 24 template<class C> object_creator()25LLVM_LIBRARY_VISIBILITY void* object_creator() { 26 return new C(); 27 } 28 29 /// object_deleter - Helper method for ManagedStatic. 30 /// 31 template <typename T> struct LLVM_LIBRARY_VISIBILITY object_deleter { callobject_deleter32 static void call(void *Ptr) { delete (T *)Ptr; } 33 }; 34 template <typename T, size_t N> 35 struct LLVM_LIBRARY_VISIBILITY object_deleter<T[N]> { 36 static void call(void *Ptr) { delete[](T *)Ptr; } 37 }; 38 39 /// ManagedStaticBase - Common base class for ManagedStatic instances. 40 class ManagedStaticBase { 41 protected: 42 // This should only be used as a static variable, which guarantees that this 43 // will be zero initialized. 44 mutable std::atomic<void *> Ptr; 45 mutable void (*DeleterFn)(void*); 46 mutable const ManagedStaticBase *Next; 47 48 void RegisterManagedStatic(void *(*creator)(), void (*deleter)(void*)) const; 49 50 public: 51 /// isConstructed - Return true if this object has not been created yet. 52 bool isConstructed() const { return Ptr != nullptr; } 53 54 void destroy() const; 55 }; 56 57 /// ManagedStatic - This transparently changes the behavior of global statics to 58 /// be lazily constructed on demand (good for reducing startup times of dynamic 59 /// libraries that link in LLVM components) and for making destruction be 60 /// explicit through the llvm_shutdown() function call. 61 /// 62 template<class C> 63 class ManagedStatic : public ManagedStaticBase { 64 public: 65 // Accessors. 66 C &operator*() { 67 void *Tmp = Ptr.load(std::memory_order_acquire); 68 if (!Tmp) 69 RegisterManagedStatic(object_creator<C>, object_deleter<C>::call); 70 71 return *static_cast<C *>(Ptr.load(std::memory_order_relaxed)); 72 } 73 74 C *operator->() { return &**this; } 75 76 const C &operator*() const { 77 void *Tmp = Ptr.load(std::memory_order_acquire); 78 if (!Tmp) 79 RegisterManagedStatic(object_creator<C>, object_deleter<C>::call); 80 81 return *static_cast<C *>(Ptr.load(std::memory_order_relaxed)); 82 } 83 84 const C *operator->() const { return &**this; } 85 }; 86 87 /// llvm_shutdown - Deallocate and destroy all ManagedStatic variables. 88 void llvm_shutdown(); 89 90 /// llvm_shutdown_obj - This is a simple helper class that calls 91 /// llvm_shutdown() when it is destroyed. 92 struct llvm_shutdown_obj { 93 llvm_shutdown_obj() = default; 94 ~llvm_shutdown_obj() { llvm_shutdown(); } 95 }; 96 97 } // end namespace llvm 98 99 #endif // LLVM_SUPPORT_MANAGEDSTATIC_H 100