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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.

 // WARNING: Thread local storage is a bit tricky to get right.  Please make

 // sure that this is really the proper solution for what you're trying to

 // achieve.  Don't prematurely optimize, most likely you can just use a Lock.

 //

 // These classes implement a warpper around the platform's TLS storage

 // mechanism.  On construction, they will allocate a TLS slot, and free the

 // TLS slot on destruction.  No memory management (creation or destruction) is

 // handled.  This means for uses of ThreadLocalPointer, you must correctly

 // manage the memory yourself, these classes will not destroy the pointer for

 // you.  There are no at-thread-exit actions taken by these classes.

 //

 // ThreadLocalPointer<Type> wraps a Type*.  It performs no creation or

 // destruction, so memory management must be handled elsewhere.  The first call

 // to Get() on a thread will return NULL.  You can update the pointer with a

 // call to Set().

 //

 // ThreadLocalBoolean wraps a bool.  It will default to false if it has never

 // been set otherwise with Set().

 //

 // Thread Safety:  An instance of ThreadLocalStorage is completely thread safe

 // once it has been created.  If you want to dynamically create an instance,

 // you must of course properly deal with safety and race conditions.  This

 // means a function-level static initializer is generally inappropiate.

 //

 // Example usage:

 //   // My class is logically attached to a single thread.  We cache a pointer

 //   // on the thread it was created on, so we can implement current().

 //   MyClass::MyClass() {

 //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() == NULL);

 //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(this);

 //   }

 //

 //   MyClass::~MyClass() {

 //     DCHECK(Singleton<ThreadLocalPointer<MyClass> >::get()->Get() != NULL);

 //     Singleton<ThreadLocalPointer<MyClass> >::get()->Set(NULL);

 //   }

 //

 //   // Return the current MyClass associated with the calling thread, can be

 //   // NULL if there isn't a MyClass associated.

 //   MyClass* MyClass::current() {

 //     return Singleton<ThreadLocalPointer<MyClass> >::get()->Get();

 //   }

 #ifndef BASE_THREAD_LOCAL_H_

 #define BASE_THREAD_LOCAL_H_

 #include "base/basictypes.h"

 #if defined(OS_POSIX)

 #include <pthread.h>

 #endif

 namespace base {

 // Helper functions that abstract the cross-platform APIs.  Do not use directly.

 struct ThreadLocalPlatform {

 #if defined(OS_WIN)

   typedef int SlotType;

 #elif defined(OS_POSIX)

   typedef pthread_key_t SlotType;

 #endif

   static void AllocateSlot(SlotType& slot);

   static void FreeSlot(SlotType& slot);

   static void* GetValueFromSlot(SlotType& slot);

   static void SetValueInSlot(SlotType& slot, void* value);

 };

 template <typename Type>

 class ThreadLocalPointer {

  public:

   ThreadLocalPointer() : slot_() {

     ThreadLocalPlatform::AllocateSlot(slot_);

   }

   ~ThreadLocalPointer() {

     ThreadLocalPlatform::FreeSlot(slot_);

   }

   Type* Get() {

     return static_cast<Type*>(ThreadLocalPlatform::GetValueFromSlot(slot_));

   }

   void Set(Type* ptr) {

     ThreadLocalPlatform::SetValueInSlot(slot_, ptr);

   }

  private:

   typedef ThreadLocalPlatform::SlotType SlotType;

   SlotType slot_;

   DISALLOW_COPY_AND_ASSIGN(ThreadLocalPointer<Type>);

 };

 class ThreadLocalBoolean {

  public:

   ThreadLocalBoolean() { }

   ~ThreadLocalBoolean() { }

   bool Get() {

     return tlp_.Get() != NULL;

   }

   void Set(bool val) {

     tlp_.Set(reinterpret_cast<void*>(val ? 1 : 0));

   }

  private:

   ThreadLocalPointer<void> tlp_;

   DISALLOW_COPY_AND_ASSIGN(ThreadLocalBoolean);

 };

 }  // namespace base

 #endif  // BASE_THREAD_LOCAL_H_