1 : // Copyright (c) 2006-2008 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
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.
8 : //
9 : // These classes implement a warpper 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.
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
19 : // call 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,
26 : // you must of course properly deal with safety and race conditions. This
27 : // means a function-level static initializer is generally inappropiate.
28 : //
29 : // Example usage:
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);
35 : // }
36 : //
37 : // MyClass::~MyClass() {
38 : // DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);
39 : // Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);
40 : // }
41 : //
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();
46 : // }
47 :
48 : #ifndef BASE_THREAD_LOCAL_H_
49 : #define BASE_THREAD_LOCAL_H_
50 :
51 : #include "base/basictypes.h"
52 :
53 : #if defined(OS_POSIX)
54 : #include <pthread.h>
55 : #endif
56 :
57 : namespace base {
58 :
59 : // Helper functions that abstract the cross-platform APIs. Do not use directly.
60 : struct ThreadLocalPlatform {
61 : #if defined(OS_WIN)
62 : typedef int SlotType;
63 : #elif defined(OS_POSIX)
64 : typedef pthread_key_t SlotType;
65 : #endif
66 :
67 : static void AllocateSlot(SlotType& slot);
68 : static void FreeSlot(SlotType& slot);
69 : static void* GetValueFromSlot(SlotType& slot);
70 : static void SetValueInSlot(SlotType& slot, void* value);
71 : };
72 :
73 : template <typename Type>
74 : class ThreadLocalPointer {
75 : public:
76 4260 : ThreadLocalPointer() : slot_() {
77 4260 : ThreadLocalPlatform::AllocateSlot(slot_);
78 4260 : }
79 :
80 4257 : ~ThreadLocalPointer() {
81 4257 : ThreadLocalPlatform::FreeSlot(slot_);
82 4257 : }
83 :
84 14199 : Type* Get() {
85 14199 : return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_));
86 : }
87 :
88 11356 : void Set(Type* ptr) {
89 11356 : ThreadLocalPlatform::SetValueInSlot(slot_, ptr);
90 11356 : }
91 :
92 : private:
93 : typedef ThreadLocalPlatform::SlotType SlotType;
94 :
95 : SlotType slot_;
96 :
97 : DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);
98 : };
99 :
100 : class ThreadLocalBoolean {
101 : public:
102 1420 : ThreadLocalBoolean() { }
103 1419 : ~ThreadLocalBoolean() { }
104 :
105 1419 : bool Get() {
106 1419 : return tlp_.Get() != NULL;
107 : }
108 :
109 2839 : void Set(bool val) {
110 2839 : tlp_.Set(reinterpret_cast<void*>(val ? 1 : 0));
111 2839 : }
112 :
113 : private:
114 : ThreadLocalPointer<void> tlp_;
115 :
116 : DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);
117 : };
118 :
119 : } // namespace base
120 :
121 : #endif // BASE_THREAD_LOCAL_H_
|