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/atomicops.h"
9 #include "base/base_export.h"
10 #include "base/macros.h"
11 #include "build/build_config.h"
12 
13 #if defined(OS_WIN)
14 #include <windows.h>
15 #elif defined(OS_POSIX)
16 #include <pthread.h>
17 #endif
18 
19 namespace base {
20 
21 namespace internal {
22 
23 // WARNING: You should *NOT* be using this class directly.
24 // PlatformThreadLocalStorage is low-level abstraction to the OS's TLS
25 // interface, you should instead be using ThreadLocalStorage::StaticSlot/Slot.
26 class BASE_EXPORT PlatformThreadLocalStorage {
27  public:
28 
29 #if defined(OS_WIN)
30   typedef unsigned long TLSKey;
31   enum : unsigned { TLS_KEY_OUT_OF_INDEXES = TLS_OUT_OF_INDEXES };
32 #elif defined(OS_POSIX)
33   typedef pthread_key_t TLSKey;
34   // The following is a "reserved key" which is used in our generic Chromium
35   // ThreadLocalStorage implementation.  We expect that an OS will not return
36   // such a key, but if it is returned (i.e., the OS tries to allocate it) we
37   // will just request another key.
38   enum { TLS_KEY_OUT_OF_INDEXES = 0x7FFFFFFF };
39 #endif
40 
41   // The following methods need to be supported on each OS platform, so that
42   // the Chromium ThreadLocalStore functionality can be constructed.
43   // Chromium will use these methods to acquire a single OS slot, and then use
44   // that to support a much larger number of Chromium slots (independent of the
45   // OS restrictions).
46   // The following returns true if it successfully is able to return an OS
47   // key in |key|.
48   static bool AllocTLS(TLSKey* key);
49   // Note: FreeTLS() doesn't have to be called, it is fine with this leak, OS
50   // might not reuse released slot, you might just reset the TLS value with
51   // SetTLSValue().
52   static void FreeTLS(TLSKey key);
53   static void SetTLSValue(TLSKey key, void* value);
54   static void* GetTLSValue(TLSKey key);
55 
56   // Each platform (OS implementation) is required to call this method on each
57   // terminating thread when the thread is about to terminate.  This method
58   // will then call all registered destructors for slots in Chromium
59   // ThreadLocalStorage, until there are no slot values remaining as having
60   // been set on this thread.
61   // Destructors may end up being called multiple times on a terminating
62   // thread, as other destructors may re-set slots that were previously
63   // destroyed.
64 #if defined(OS_WIN)
65   // Since Windows which doesn't support TLS destructor, the implementation
66   // should use GetTLSValue() to retrieve the value of TLS slot.
67   static void OnThreadExit();
68 #elif defined(OS_POSIX)
69   // |Value| is the data stored in TLS slot, The implementation can't use
70   // GetTLSValue() to retrieve the value of slot as it has already been reset
71   // in Posix.
72   static void OnThreadExit(void* value);
73 #endif
74 };
75 
76 }  // namespace internal
77 
78 // Wrapper for thread local storage.  This class doesn't do much except provide
79 // an API for portability.
80 class BASE_EXPORT ThreadLocalStorage {
81  public:
82 
83   // Prototype for the TLS destructor function, which can be optionally used to
84   // cleanup thread local storage on thread exit.  'value' is the data that is
85   // stored in thread local storage.
86   typedef void (*TLSDestructorFunc)(void* value);
87 
88   // StaticSlot uses its own struct initializer-list style static
89   // initialization, as base's LINKER_INITIALIZED requires a constructor and on
90   // some compilers (notably gcc 4.4) this still ends up needing runtime
91   // initialization.
92   #define TLS_INITIALIZER {false, 0}
93 
94   // A key representing one value stored in TLS.
95   // Initialize like
96   //   ThreadLocalStorage::StaticSlot my_slot = TLS_INITIALIZER;
97   // If you're not using a static variable, use the convenience class
98   // ThreadLocalStorage::Slot (below) instead.
99   struct BASE_EXPORT StaticSlot {
100     // Set up the TLS slot.  Called by the constructor.
101     // 'destructor' is a pointer to a function to perform per-thread cleanup of
102     // this object.  If set to NULL, no cleanup is done for this TLS slot.
103     void Initialize(TLSDestructorFunc destructor);
104 
105     // Free a previously allocated TLS 'slot'.
106     // If a destructor was set for this slot, removes
107     // the destructor so that remaining threads exiting
108     // will not free data.
109     void Free();
110 
111     // Get the thread-local value stored in slot 'slot'.
112     // Values are guaranteed to initially be zero.
113     void* Get() const;
114 
115     // Set the thread-local value stored in slot 'slot' to
116     // value 'value'.
117     void Set(void* value);
118 
initializedStaticSlot119     bool initialized() const {
120       return base::subtle::Acquire_Load(&initialized_) != 0;
121     }
122 
123     // The internals of this struct should be considered private.
124     base::subtle::Atomic32 initialized_;
125     int slot_;
126   };
127 
128   // A convenience wrapper around StaticSlot with a constructor. Can be used
129   // as a member variable.
130   class BASE_EXPORT Slot : public StaticSlot {
131    public:
132     // Calls StaticSlot::Initialize().
133     explicit Slot(TLSDestructorFunc destructor = NULL);
134 
135    private:
136     using StaticSlot::initialized_;
137     using StaticSlot::slot_;
138 
139     DISALLOW_COPY_AND_ASSIGN(Slot);
140   };
141 
142  private:
143   DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
144 };
145 
146 }  // namespace base
147 
148 #endif  // BASE_THREADING_THREAD_LOCAL_STORAGE_H_
149