1 // Copyright 2013 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.
5 // WARNING: Thread local storage is a bit tricky to get right. Please make
6 // sure that this is really the proper solution for what you're trying to
7 // achieve. Don't prematurely optimize, most likely you can just use a Lock.
9 // These classes implement a wrapper around the platform's TLS storage
10 // mechanism. On construction, they will allocate a TLS slot, and free the
11 // TLS slot on destruction. No memory management (creation or destruction) is
12 // handled. This means for uses of ThreadLocalPointer, you must correctly
13 // manage the memory yourself, these classes will not destroy the pointer for
14 // you. There are no at-thread-exit actions taken by these classes.
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
21 // ThreadLocalBoolean wraps a bool. It will default to false if it has never
22 // been set otherwise with Set().
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,
26 // you must of course properly deal with safety and race conditions. This
27 // means a function-level static initializer is generally inappropiate.
30 // // My class is logically attached to a single thread. We cache a pointer
31 // // on the thread it was created on, so we can implement current().
32 // MyClass::MyClass() {
33 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);
34 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);
37 // MyClass::~MyClass() {
38 // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
39 // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
42 // // Return the current MyClass associated with the calling thread, can be
43 // // NULL if there isn't a MyClass associated.
44 // MyClass* MyClass::current() {
45 // return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();
48 #ifndef MOJO_PUBLIC_UTILITY_THREAD_LOCAL_H_
49 #define MOJO_PUBLIC_UTILITY_THREAD_LOCAL_H_
55 #include "mojo/public/system/macros.h"
60 // Helper functions that abstract the cross-platform APIs. Do not use directly.
61 struct ThreadLocalPlatform {
63 typedef unsigned long SlotType;
65 typedef pthread_key_t SlotType;
68 static void AllocateSlot(SlotType* slot);
69 static void FreeSlot(SlotType slot);
70 static void* GetValueFromSlot(SlotType slot);
71 static void SetValueInSlot(SlotType slot, void* value);
74 } // namespace internal
76 template <typename Type>
77 class ThreadLocalPointer {
79 ThreadLocalPointer() : slot_() {
80 internal::ThreadLocalPlatform::AllocateSlot(&slot_);
83 ~ThreadLocalPointer() {
84 internal::ThreadLocalPlatform::FreeSlot(slot_);
88 return static_cast<Type*>(
89 internal::ThreadLocalPlatform::GetValueFromSlot(slot_));
93 internal::ThreadLocalPlatform::SetValueInSlot(
94 slot_, const_cast<void*>(static_cast<const void*>(ptr)));
98 typedef internal::ThreadLocalPlatform::SlotType SlotType;
102 MOJO_DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
105 class ThreadLocalBoolean {
107 ThreadLocalBoolean() {}
108 ~ThreadLocalBoolean() {}
111 return tlp_.Get() != NULL;
115 tlp_.Set(val ? this : NULL);
119 ThreadLocalPointer<void> tlp_;
121 MOJO_DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
126 #endif // MOJO_PUBLIC_UTILITY_THREAD_LOCAL_H_