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#ifndef BASE_THREADING_THREAD_LOCAL_STORAGE_H_
6#define BASE_THREADING_THREAD_LOCAL_STORAGE_H_
7#pragma once
8
9#include "base/base_api.h"
10#include "base/basictypes.h"
11
12#if defined(OS_POSIX)
13#include <pthread.h>
14#endif
15
16namespace base {
17
18// Wrapper for thread local storage.  This class doesn't do much except provide
19// an API for portability.
20class BASE_API ThreadLocalStorage {
21 public:
22
23  // Prototype for the TLS destructor function, which can be optionally used to
24  // cleanup thread local storage on thread exit.  'value' is the data that is
25  // stored in thread local storage.
26  typedef void (*TLSDestructorFunc)(void* value);
27
28  // A key representing one value stored in TLS.
29  class BASE_API Slot {
30   public:
31    explicit Slot(TLSDestructorFunc destructor = NULL);
32
33    // This constructor should be used for statics.
34    // It returns an uninitialized Slot.
35    explicit Slot(base::LinkerInitialized x) {}
36
37    // Set up the TLS slot.  Called by the constructor.
38    // 'destructor' is a pointer to a function to perform per-thread cleanup of
39    // this object.  If set to NULL, no cleanup is done for this TLS slot.
40    // Returns false on error.
41    bool Initialize(TLSDestructorFunc destructor);
42
43    // Free a previously allocated TLS 'slot'.
44    // If a destructor was set for this slot, removes
45    // the destructor so that remaining threads exiting
46    // will not free data.
47    void Free();
48
49    // Get the thread-local value stored in slot 'slot'.
50    // Values are guaranteed to initially be zero.
51    void* Get() const;
52
53    // Set the thread-local value stored in slot 'slot' to
54    // value 'value'.
55    void Set(void* value);
56
57    bool initialized() const { return initialized_; }
58
59   private:
60    // The internals of this struct should be considered private.
61    bool initialized_;
62#if defined(OS_WIN)
63    int slot_;
64#elif defined(OS_POSIX)
65    pthread_key_t key_;
66#endif
67
68    DISALLOW_COPY_AND_ASSIGN(Slot);
69  };
70
71#if defined(OS_WIN)
72  // Function called when on thread exit to call TLS
73  // destructor functions.  This function is used internally.
74  static void ThreadExit();
75
76 private:
77  // Function to lazily initialize our thread local storage.
78  static void **Initialize();
79
80 private:
81  // The maximum number of 'slots' in our thread local storage stack.
82  // For now, this is fixed.  We could either increase statically, or
83  // we could make it dynamic in the future.
84  static const int kThreadLocalStorageSize = 64;
85
86  static long tls_key_;
87  static long tls_max_;
88  static TLSDestructorFunc tls_destructors_[kThreadLocalStorageSize];
89#endif  // OS_WIN
90
91  DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
92};
93
94}  // namespace base
95
96#endif  // BASE_THREADING_THREAD_LOCAL_STORAGE_H_
97