1// Copyright (c) 2012 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#ifndef BASE_THREADING_THREAD_LOCAL_STORAGE_H_
6#define BASE_THREADING_THREAD_LOCAL_STORAGE_H_
7
8#include "base/base_export.h"
9#include "base/basictypes.h"
10
11#if defined(OS_WIN)
12#include <windows.h>
13#elif defined(OS_POSIX)
14#include <pthread.h>
15#endif
16
17namespace base {
18
19namespace internal {
20
21// WARNING: You should *NOT* be using this class directly.
22// PlatformThreadLocalStorage is low-level abstraction to the OS's TLS
23// interface, you should instead be using ThreadLocalStorage::StaticSlot/Slot.
24class BASE_EXPORT PlatformThreadLocalStorage {
25 public:
26
27#if defined(OS_WIN)
28  typedef unsigned long TLSKey;
29  enum { TLS_KEY_OUT_OF_INDEXES = TLS_OUT_OF_INDEXES };
30#elif defined(OS_POSIX)
31  typedef pthread_key_t TLSKey;
32  // The following is a "reserved key" which is used in our generic Chromium
33  // ThreadLocalStorage implementation.  We expect that an OS will not return
34  // such a key, but if it is returned (i.e., the OS tries to allocate it) we
35  // will just request another key.
36  enum { TLS_KEY_OUT_OF_INDEXES = 0x7FFFFFFF };
37#endif
38
39  // The following methods need to be supported on each OS platform, so that
40  // the Chromium ThreadLocalStore functionality can be constructed.
41  // Chromium will use these methods to acquire a single OS slot, and then use
42  // that to support a much larger number of Chromium slots (independent of the
43  // OS restrictions).
44  // The following returns true if it successfully is able to return an OS
45  // key in |key|.
46  static bool AllocTLS(TLSKey* key);
47  // Note: FreeTLS() doesn't have to be called, it is fine with this leak, OS
48  // might not reuse released slot, you might just reset the TLS value with
49  // SetTLSValue().
50  static void FreeTLS(TLSKey key);
51  static void SetTLSValue(TLSKey key, void* value);
52  static void* GetTLSValue(TLSKey key);
53
54  // Each platform (OS implementation) is required to call this method on each
55  // terminating thread when the thread is about to terminate.  This method
56  // will then call all registered destructors for slots in Chromium
57  // ThreadLocalStorage, until there are no slot values remaining as having
58  // been set on this thread.
59  // Destructors may end up being called multiple times on a terminating
60  // thread, as other destructors may re-set slots that were previously
61  // destroyed.
62#if defined(OS_WIN)
63  // Since Windows which doesn't support TLS destructor, the implementation
64  // should use GetTLSValue() to retrieve the value of TLS slot.
65  static void OnThreadExit();
66#elif defined(OS_POSIX)
67  // |Value| is the data stored in TLS slot, The implementation can't use
68  // GetTLSValue() to retrieve the value of slot as it has already been reset
69  // in Posix.
70  static void OnThreadExit(void* value);
71#endif
72};
73
74}  // namespace internal
75
76// Wrapper for thread local storage.  This class doesn't do much except provide
77// an API for portability.
78class BASE_EXPORT ThreadLocalStorage {
79 public:
80
81  // Prototype for the TLS destructor function, which can be optionally used to
82  // cleanup thread local storage on thread exit.  'value' is the data that is
83  // stored in thread local storage.
84  typedef void (*TLSDestructorFunc)(void* value);
85
86  // StaticSlot uses its own struct initializer-list style static
87  // initialization, as base's LINKER_INITIALIZED requires a constructor and on
88  // some compilers (notably gcc 4.4) this still ends up needing runtime
89  // initialization.
90  #define TLS_INITIALIZER {0}
91
92  // A key representing one value stored in TLS.
93  // Initialize like
94  //   ThreadLocalStorage::StaticSlot my_slot = TLS_INITIALIZER;
95  // If you're not using a static variable, use the convenience class
96  // ThreadLocalStorage::Slot (below) instead.
97  struct BASE_EXPORT StaticSlot {
98    // Set up the TLS slot.  Called by the constructor.
99    // 'destructor' is a pointer to a function to perform per-thread cleanup of
100    // this object.  If set to NULL, no cleanup is done for this TLS slot.
101    // Returns false on error.
102    bool Initialize(TLSDestructorFunc destructor);
103
104    // Free a previously allocated TLS 'slot'.
105    // If a destructor was set for this slot, removes
106    // the destructor so that remaining threads exiting
107    // will not free data.
108    void Free();
109
110    // Get the thread-local value stored in slot 'slot'.
111    // Values are guaranteed to initially be zero.
112    void* Get() const;
113
114    // Set the thread-local value stored in slot 'slot' to
115    // value 'value'.
116    void Set(void* value);
117
118    bool initialized() const { return initialized_; }
119
120    // The internals of this struct should be considered private.
121    bool initialized_;
122    int slot_;
123  };
124
125  // A convenience wrapper around StaticSlot with a constructor. Can be used
126  // as a member variable.
127  class BASE_EXPORT Slot : public StaticSlot {
128   public:
129    // Calls StaticSlot::Initialize().
130    explicit Slot(TLSDestructorFunc destructor = NULL);
131
132   private:
133    using StaticSlot::initialized_;
134    using StaticSlot::slot_;
135
136    DISALLOW_COPY_AND_ASSIGN(Slot);
137  };
138
139  DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
140};
141
142}  // namespace base
143
144#endif  // BASE_THREADING_THREAD_LOCAL_STORAGE_H_
145