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//
// ThreadLocal.h
//
// 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.
//
// SPDX-License-Identifier: BSL-1.0
//
#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
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