ipc/chromium/src/base/thread_local_storage.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
   4 // Use of this source code is governed by a BSD-style license that can be
   5 // found in the LICENSE file.
   6
   7 #ifndef BASE_THREAD_LOCAL_STORAGE_H_
   8 #define BASE_THREAD_LOCAL_STORAGE_H_
   9
  10 #include "base/basictypes.h"
  11
  12 #if defined(XP_UNIX)
  13 #  include <pthread.h>
  14 #endif
  15
  16 // Wrapper for thread local storage.  This class doesn't do much except provide
  17 // an API for portability.
  18 class ThreadLocalStorage {
  19  public:
  20   // Prototype for the TLS destructor function, which can be optionally used to
  21   // cleanup thread local storage on thread exit.  'value' is the data that is
  22   // stored in thread local storage.
  23   typedef void (*TLSDestructorFunc)(void* value);
  24
  25   // A key representing one value stored in TLS.
  26   class Slot {
  27    public:
  28     explicit Slot(TLSDestructorFunc destructor = NULL);
  29
  30     // This constructor should be used for statics.
  31     // It returns an uninitialized Slot.
  32     explicit Slot(base::LinkerInitialized x) {}
  33
  34     // Set up the TLS slot.  Called by the constructor.
  35     // 'destructor' is a pointer to a function to perform per-thread cleanup of
  36     // this object.  If set to NULL, no cleanup is done for this TLS slot.
  37     // Returns false on error.
  38     bool Initialize(TLSDestructorFunc destructor);
  39
  40     // Free a previously allocated TLS 'slot'.
  41     // If a destructor was set for this slot, removes
  42     // the destructor so that remaining threads exiting
  43     // will not free data.
  44     void Free();
  45
  46     // Get the thread-local value stored in slot 'slot'.
  47     // Values are guaranteed to initially be zero.
  48     void* Get() const;
  49
  50     // Set the thread-local value stored in slot 'slot' to
  51     // value 'value'.
  52     void Set(void* value);
  53
  54     bool initialized() const { return initialized_; }
  55
  56    private:
  57     // The internals of this struct should be considered private.
  58     bool initialized_;
  59 #if defined(XP_WIN)
  60     int slot_;
  61 #else
  62     pthread_key_t key_;
  63 #endif
  64
  65     DISALLOW_COPY_AND_ASSIGN(Slot);
  66   };
  67
  68 #if defined(XP_WIN)
  69   // Function called when on thread exit to call TLS
  70   // destructor functions.  This function is used internally.
  71   static void ThreadExit();
  72
  73  private:
  74   // Function to lazily initialize our thread local storage.
  75   static void** Initialize();
  76
  77  private:
  78   // The maximum number of 'slots' in our thread local storage stack.
  79   // For now, this is fixed.  We could either increase statically, or
  80   // we could make it dynamic in the future.
  81   static const int kThreadLocalStorageSize = 64;
  82
  83   static long tls_key_;
  84   static long tls_max_;
  85   static TLSDestructorFunc tls_destructors_[kThreadLocalStorageSize];
  86 #endif  // XP_WIN
  87
  88   DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);
  89 };
  90
  91 // Temporary backwards-compatible name.
  92 // TODO(evanm): replace all usage of TLSSlot.
  93 typedef ThreadLocalStorage::Slot TLSSlot;
  94
  95 #endif  // BASE_THREAD_LOCAL_STORAGE_H_