source: XMLIO_V2/external/include/Poco/ThreadLocal.h @ 80

//
// ThreadLocal.h
//
// $Id: //poco/1.3/Foundation/include/Poco/ThreadLocal.h#1 $
//
// 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 {


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


template <class C>
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;
};


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:
        typedef std::map<const void*, TLSAbstractSlot*> TLSMap;
        
        TLSMap _map;

        friend class Thread;
};


template <class C>
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();
        }
        
        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();
        }

        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