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/**
* @file llhandle.h
* @brief "Handle" to an object (usually a floater) whose lifetime you don't
* control.
*
* $LicenseInfo:firstyear=2001&license=viewerlgpl$
* Second Life Viewer Source Code
* Copyright (C) 2010, Linden Research, Inc.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation;
* version 2.1 of the License only.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
* Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA
* $/LicenseInfo$
*/
#ifndef LLHANDLE_H
#define LLHANDLE_H
#include "llpointer.h"
template <typename T>
class LLTombStone : public LLRefCount
{
public:
LLTombStone(T* target = NULL) : mTarget(target) {}
void setTarget(T* target) { mTarget = target; }
T* getTarget() const { return mTarget; }
private:
T* mTarget;
};
// LLHandles are used to refer to objects whose lifetime you do not control or influence.
// Calling get() on a handle will return a pointer to the referenced object or NULL,
// if the object no longer exists. Note that during the lifetime of the returned pointer,
// you are assuming that the object will not be deleted by any action you perform,
// or any other thread, as normal when using pointers, so avoid using that pointer outside of
// the local code block.
//
// https://wiki.lindenlab.com/mediawiki/index.php?title=LLHandle&oldid=79669
template <typename T>
class LLHandle
{
public:
LLHandle() : mTombStone(getDefaultTombStone()) {}
const LLHandle<T>& operator =(const LLHandle<T>& other)
{
mTombStone = other.mTombStone;
return *this;
}
bool isDead() const
{
return mTombStone->getTarget() == NULL;
}
void markDead()
{
mTombStone = getDefaultTombStone();
}
T* get() const
{
return mTombStone->getTarget();
}
friend bool operator== (const LLHandle<T>& lhs, const LLHandle<T>& rhs)
{
return lhs.mTombStone == rhs.mTombStone;
}
friend bool operator!= (const LLHandle<T>& lhs, const LLHandle<T>& rhs)
{
return !(lhs == rhs);
}
friend bool operator< (const LLHandle<T>& lhs, const LLHandle<T>& rhs)
{
return lhs.mTombStone < rhs.mTombStone;
}
friend bool operator> (const LLHandle<T>& lhs, const LLHandle<T>& rhs)
{
return lhs.mTombStone > rhs.mTombStone;
}
protected:
LLPointer<LLTombStone<T> > mTombStone;
private:
static LLPointer<LLTombStone<T> >& getDefaultTombStone()
{
static LLPointer<LLTombStone<T> > sDefaultTombStone = new LLTombStone<T>;
return sDefaultTombStone;
}
};
template <typename T>
class LLRootHandle : public LLHandle<T>
{
public:
LLRootHandle(T* object) { bind(object); }
LLRootHandle() {};
~LLRootHandle() { unbind(); }
// this is redundant, since a LLRootHandle *is* an LLHandle
LLHandle<T> getHandle() { return LLHandle<T>(*this); }
void bind(T* object)
{
// unbind existing tombstone
if (LLHandle<T>::mTombStone.notNull())
{
if (LLHandle<T>::mTombStone->getTarget() == object) return;
LLHandle<T>::mTombStone->setTarget(NULL);
}
// tombstone reference counted, so no paired delete
LLHandle<T>::mTombStone = new LLTombStone<T>(object);
}
void unbind()
{
LLHandle<T>::mTombStone->setTarget(NULL);
}
//don't allow copying of root handles, since there should only be one
private:
LLRootHandle(const LLRootHandle& other) {};
};
// Use this as a mixin for simple classes that need handles and when you don't
// want handles at multiple points of the inheritance hierarchy
template <typename T>
class LLHandleProvider
{
protected:
typedef LLHandle<T> handle_type_t;
LLHandleProvider()
{
// provided here to enforce T deriving from LLHandleProvider<T>
}
LLHandle<T> getHandle()
{
// perform lazy binding to avoid small tombstone allocations for handle
// providers whose handles are never referenced
mHandle.bind(static_cast<T*>(this));
return mHandle;
}
private:
LLRootHandle<T> mHandle;
};
#endif
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