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ThreadLocal.h

//
// ThreadLocal.h
//
// $Id: //poco/1.2/Foundation/include/Poco/ThreadLocal.h#2 $
//
// Library: Foundation
// Package: Threading
// Module:  Thread
//
// Definition of the ThreadLocal template and related classes.
//
// Copyright (c) 2004-2006, Applied Informatics Software Engineering GmbH.
// and Contributors.
//
// Permission is hereby granted, free of charge, to any person or organization
// obtaining a copy of the software and accompanying documentation covered by
// this license (the "Software") to use, reproduce, display, distribute,
// execute, and transmit the Software, and to prepare derivative works of the
// Software, and to permit third-parties to whom the Software is furnished to
// do so, all subject to the following:
// 
// The copyright notices in the Software and this entire statement, including
// the above license grant, this restriction and the following disclaimer,
// must be included in all copies of the Software, in whole or in part, and
// all derivative works of the Software, unless such copies or derivative
// works are solely in the form of machine-executable object code generated by
// a source language processor.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
// SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
// FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
// ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
//


#ifndef Foundation_ThreadLocal_INCLUDED
#define Foundation_ThreadLocal_INCLUDED


#include "Poco/Foundation.h"
#include <map>


namespace Poco {


00050 class Foundation_API TLSAbstractSlot
      /// This is the base class for all objects
      /// that the ThreadLocalStorage class manages.
{
public:
      TLSAbstractSlot();
      virtual ~TLSAbstractSlot();
};


template <class C>
00061 class TLSSlot: public TLSAbstractSlot
      /// The Slot template wraps another class
      /// so that it can be stored in a ThreadLocalStorage
      /// object. This class is used internally, and you
      /// must not create instances of it yourself.
{
public:
      TLSSlot():
            _value()
      {
      }
      
      ~TLSSlot()
      {
      }
      
      C& value()
      {
            return _value;
      }
      
private:
      TLSSlot(const TLSSlot&);
      TLSSlot& operator = (const TLSSlot&);

      C _value;
};


00090 class Foundation_API ThreadLocalStorage
      /// This class manages the local storage for each thread.
      /// Never use this class directly, always use the
      /// ThreadLocal template for managing thread local storage.
{
public:
      ThreadLocalStorage();
            /// Creates the TLS.
            
      ~ThreadLocalStorage();
            /// Deletes the TLS.

      TLSAbstractSlot*& get(const void* key);
            /// Returns the slot for the given key.
            
      static ThreadLocalStorage& current();
            /// Returns the TLS object for the current thread
            /// (which may also be the main thread).
            
      static void clear();
            /// Clears the current thread's TLS object.
            /// Does nothing in the main thread.
      
private:
00114       typedef std::map<const void*, TLSAbstractSlot*> TLSMap;
      
      TLSMap _map;

      friend class Thread;
};


template <class C>
00123 class ThreadLocal
      /// This template is used to declare type safe thread
      /// local variables. It can basically be used like
      /// a smart pointer class with the special feature
      /// that it references a different object
      /// in every thread. The underlying object will
      /// be created when it is referenced for the first
      /// time.
      /// See the NestedDiagnosticContext class for an
      /// example how to use this template.
      /// Every thread only has access to its own
      /// thread local data. There is no way for a thread
      /// to access another thread's local data.
{
      typedef TLSSlot<C> Slot;

public:
      ThreadLocal()
      {
      }
      
      ~ThreadLocal()
      {
      }
      
      C* operator -> ()
      {
            return &get();
      }
      
00153       C& operator * ()
            /// "Dereferences" the smart pointer and returns a reference
            /// to the underlying data object. The reference can be used
            /// to modify the object.
      {
            return get();
      }

00161       C& get()
            /// Returns a reference to the underlying data object.
            /// The reference can be used to modify the object.
      {
            TLSAbstractSlot*& p = ThreadLocalStorage::current().get(this);
            if (!p) p = new Slot;
            return static_cast<Slot*>(p)->value();
      }
      
private:
      ThreadLocal(const ThreadLocal&);
      ThreadLocal& operator = (const ThreadLocal&);
};


} // namespace Poco


#endif // Foundation_ThreadLocal_INCLUDED

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