thread_local_storage.h

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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

/* vim: set ts=8 sts=2 et sw=2 tw=80: */

// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.

// Use of this source code is governed by a BSD-style license that can be

// found in the LICENSE file.

#ifndef BASE_THREAD_LOCAL_STORAGE_H_

#define BASE_THREAD_LOCAL_STORAGE_H_

#include "base/basictypes.h"

#if defined(XP_UNIX)

#  include <pthread.h>

#endif

// Wrapper for thread local storage.  This class doesn't do much except provide

// an API for portability.

class ThreadLocalStorage {

 public:

  // Prototype for the TLS destructor function, which can be optionally used to

  // cleanup thread local storage on thread exit.  'value' is the data that is

  // stored in thread local storage.

  typedef void (*TLSDestructorFunc)(void* value);

  // A key representing one value stored in TLS.

  class Slot {

   public:

    explicit Slot(TLSDestructorFunc destructor = NULL);

    // This constructor should be used for statics.

    // It returns an uninitialized Slot.

    explicit Slot(base::LinkerInitialized x) {}

    // Set up the TLS slot.  Called by the constructor.

    // 'destructor' is a pointer to a function to perform per-thread cleanup of

    // this object.  If set to NULL, no cleanup is done for this TLS slot.

    // Returns false on error.

    bool Initialize(TLSDestructorFunc destructor);

    // Free a previously allocated TLS 'slot'.

    // If a destructor was set for this slot, removes

    // the destructor so that remaining threads exiting

    // will not free data.

    void Free();

    // Get the thread-local value stored in slot 'slot'.

    // Values are guaranteed to initially be zero.

    void* Get() const;

    // Set the thread-local value stored in slot 'slot' to

    // value 'value'.

    void Set(void* value);

    bool initialized() const { return initialized_; }

   private:

    // The internals of this struct should be considered private.

    bool initialized_;

#if defined(XP_WIN)

    int slot_;

#else

    pthread_key_t key_;

#endif

    DISALLOW_COPY_AND_ASSIGN(Slot);

};

#if defined(XP_WIN)

  // Function called when on thread exit to call TLS

  // destructor functions.  This function is used internally.

  static void ThreadExit();

 private:

  // Function to lazily initialize our thread local storage.

  static void** Initialize();

 private:

  // The maximum number of 'slots' in our thread local storage stack.

  // For now, this is fixed.  We could either increase statically, or

  // we could make it dynamic in the future.

  static const int kThreadLocalStorageSize = 64;

  static long tls_key_;

  static long tls_max_;

  static TLSDestructorFunc tls_destructors_[kThreadLocalStorageSize];

#endif  // XP_WIN

  DISALLOW_COPY_AND_ASSIGN(ThreadLocalStorage);

};

// Temporary backwards-compatible name.

// TODO(evanm): replace all usage of TLSSlot.

typedef ThreadLocalStorage::Slot TLSSlot;

#endif  // BASE_THREAD_LOCAL_STORAGE_H_