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 // 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(OS_POSIX)

 #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:

     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(OS_WIN)

     int slot_;

 #elif defined(OS_POSIX)

     pthread_key_t key_;

 #endif

     DISALLOW_COPY_AND_ASSIGN(Slot);

   };

 #if defined(OS_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  // OS_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_