1 // Copyright (c) 2011 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 // WARNING: Thread local storage is a bit tricky to get right. Please make sure 6 // that this is really the proper solution for what you're trying to achieve. 7 // Don't prematurely optimize, most likely you can just use a Lock. 8 // 9 // These classes implement a wrapper around ThreadLocalStorage::Slot. On 10 // construction, they will allocate a TLS slot, and free the TLS slot on 11 // destruction. No memory management (creation or destruction) is handled. This 12 // means for uses of ThreadLocalPointer, you must correctly manage the memory 13 // yourself, these classes will not destroy the pointer for you. There are no 14 // at-thread-exit actions taken by these classes. 15 // 16 // ThreadLocalPointer<Type> wraps a Type*. It performs no creation or 17 // destruction, so memory management must be handled elsewhere. The first call 18 // to Get() on a thread will return NULL. You can update the pointer with a call 19 // to Set(). 20 // 21 // ThreadLocalBoolean wraps a bool. It will default to false if it has never 22 // been set otherwise with Set(). 23 // 24 // Thread Safety: An instance of ThreadLocalStorage is completely thread safe 25 // once it has been created. If you want to dynamically create an instance, you 26 // must of course properly deal with safety and race conditions. This means a 27 // function-level static initializer is generally inappropiate. 28 // 29 // In Android, the system TLS is limited. 30 // 31 // Example usage: 32 // // My class is logically attached to a single thread. We cache a pointer 33 // // on the thread it was created on, so we can implement current(). 34 // MyClass::MyClass() { 35 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL); 36 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this); 37 // } 38 // 39 // MyClass::~MyClass() { 40 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL); 41 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL); 42 // } 43 // 44 // // Return the current MyClass associated with the calling thread, can be 45 // // NULL if there isn't a MyClass associated. 46 // MyClass* MyClass::current() { 47 // return Singleton<ThreadLocalPointer<MyClass> >::get()->Get(); 48 // } 49 50 #ifndef BASE_THREADING_THREAD_LOCAL_H_ 51 #define BASE_THREADING_THREAD_LOCAL_H_ 52 53 #include "base/macros.h" 54 #include "base/threading/thread_local_storage.h" 55 56 namespace base { 57 58 template <typename Type> 59 class ThreadLocalPointer { 60 public: 61 ThreadLocalPointer() = default; 62 ~ThreadLocalPointer() = default; 63 64 Type* Get() { 65 return static_cast<Type*>(slot_.Get()); 66 } 67 68 void Set(Type* ptr) { 69 slot_.Set(const_cast<void*>(static_cast<const void*>(ptr))); 70 } 71 72 private: 73 ThreadLocalStorage::Slot slot_; 74 75 DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>); 76 }; 77 78 class ThreadLocalBoolean { 79 public: 80 ThreadLocalBoolean() = default; 81 ~ThreadLocalBoolean() = default; 82 83 bool Get() { 84 return tlp_.Get() != nullptr; 85 } 86 87 void Set(bool val) { 88 tlp_.Set(val ? this : nullptr); 89 } 90 91 private: 92 ThreadLocalPointer<void> tlp_; 93 94 DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean); 95 }; 96 97 } // namespace base 98 99 #endif // BASE_THREADING_THREAD_LOCAL_H_ 100
