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/**
* @file llkeyusetracker.h
* @brief Declaration of the LLKeyUseTracker class.
*
* $LicenseInfo:firstyear=2003&license=viewerlgpl$
* 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 LL_KEYUSETRACKER_H
#define LL_KEYUSETRACKER_H
// This is a generic cache for an arbitrary data type indexed against an
// arbitrary key type. The cache length is determined by expiration time
// tince against last use and set size. The age of elements and the size
// of the cache are queryable.
//
// This is implemented as a list, which makes search O(n). If you reuse this
// for something with a large dataset, consider reimplementing with a Boost
// multimap based on both a map(key) and priority queue(last_use).
template <class TKey, class TData>
class KeyUseTrackerNodeImpl
{
public:
U64 mLastUse;
U32 mUseCount;
TKey mKey;
TData mData;
KeyUseTrackerNodeImpl( TKey k, TData d ) :
mLastUse(0),
mUseCount(0),
mKey( k ),
mData( d )
{
}
};
template <class TKey, class TData>
class LLKeyUseTracker
{
typedef KeyUseTrackerNodeImpl<TKey,TData> TKeyUseTrackerNode;
typedef std::list<TKeyUseTrackerNode *> TKeyList;
TKeyList mKeyList;
U64 mMemUsecs;
U64 mLastExpire;
U32 mMaxCount;
U32 mCount;
static U64 getTime()
{
// This function operates on a frame basis, not instantaneous.
// We can rely on its output for determining first use in a
// frame.
return LLFrameTimer::getTotalTime();
}
void ageKeys()
{
U64 now = getTime();
if( now == mLastExpire )
{
return;
}
mLastExpire = now;
while( !mKeyList.empty() && (now - mKeyList.front()->mLastUse > mMemUsecs ) )
{
delete mKeyList.front();
mKeyList.pop_front();
mCount--;
}
}
TKeyUseTrackerNode *findNode( TKey key )
{
ageKeys();
typename TKeyList::iterator i;
for( i = mKeyList.begin(); i != mKeyList.end(); i++ )
{
if( (*i)->mKey == key )
return *i;
}
return NULL;
}
TKeyUseTrackerNode *removeNode( TKey key )
{
TKeyUseTrackerNode *i;
i = findNode( key );
if( i )
{
mKeyList.remove( i );
mCount--;
return i;
}
return NULL;
}
public:
LLKeyUseTracker( U32 memory_seconds, U32 max_count ) :
mLastExpire(0),
mMaxCount( max_count ),
mCount(0)
{
mMemUsecs = ((U64)memory_seconds) * 1000000;
}
~LLKeyUseTracker()
{
// Flush list
while( !mKeyList.empty() )
{
delete mKeyList.front();
mKeyList.pop_front();
mCount--;
}
}
void markUse( TKey key, TData data )
{
TKeyUseTrackerNode *node = removeNode( key );
if( !node )
{
node = new TKeyUseTrackerNode(key, data);
}
else
{
// Update data
node->mData = data;
}
node->mLastUse = getTime();
node->mUseCount++;
mKeyList.push_back( node );
mCount++;
// Too many items? Drop head
if( mCount > mMaxCount )
{
delete mKeyList.front();
mKeyList.pop_front();
mCount--;
}
}
void forgetKey( TKey key )
{
TKeyUseTrackerNode *node = removeNode( key );
if( node )
{
delete node;
}
}
U32 getUseCount( TKey key )
{
TKeyUseTrackerNode *node = findNode( key );
if( node )
{
return node->mUseCount;
}
return 0;
}
U64 getTimeSinceUse( TKey key )
{
TKeyUseTrackerNode *node = findNode( key );
if( node )
{
U64 now = getTime();
U64 delta = now - node->mLastUse;
return (U32)( delta / 1000000 );
}
return 0;
}
TData *getLastUseData( TKey key )
{
TKeyUseTrackerNode *node = findNode( key );
if( node )
{
return &node->mData;
}
return NULL;
}
U32 getKeyCount()
{
return mCount;
}
};
#endif
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