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memcache.cpp：源码内容
							/* ***** BEGIN LICENSE BLOCK ***** 
 * Version: RCSL 1.0/RPSL 1.0 
 *  
 * Portions Copyright (c) 1995-2002 RealNetworks, Inc. All Rights Reserved. 
 *      
 * The contents of this file, and the files included with this file, are 
 * subject to the current version of the RealNetworks Public Source License 
 * Version 1.0 (the "RPSL") available at 
 * http://www.helixcommunity.org/content/rpsl unless you have licensed 
 * the file under the RealNetworks Community Source License Version 1.0 
 * (the "RCSL") available at http://www.helixcommunity.org/content/rcsl, 
 * in which case the RCSL will apply. You may also obtain the license terms 
 * directly from RealNetworks.  You may not use this file except in 
 * compliance with the RPSL or, if you have a valid RCSL with RealNetworks 
 * applicable to this file, the RCSL.  Please see the applicable RPSL or 
 * RCSL for the rights, obligations and limitations governing use of the 
 * contents of the file.  
 *  
 * This file is part of the Helix DNA Technology. RealNetworks is the 
 * developer of the Original Code and owns the copyrights in the portions 
 * it created. 
 *  
 * This file, and the files included with this file, is distributed and made 
 * available on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER 
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 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS 
 * FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. 
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 * 
 * Contributor(s): 
 *  
 * ***** END LICENSE BLOCK ***** */ 
#include "hxtypes.h"
#include "hxcom.h"      // IUnknown
#include "hxiids.h"     // GUIDs
#include "hxslist.h"    // CHXSimpleList
#include "hxthread.h"   // HXMutex
#include "hxstring.h"   // memcpy()
#include "hxcomm.h"     // IHXCommonClassFactory
#include "ihxpckts.h"   // IHXBuffer
#include "hxcache2.h"   // IHXCache2, IHXCacheObject, IHXCacheObjectResponse
#include "memcache.h"
#include "multilog.h"
#include "mlog_http.h"
/****************************************************************************
 *  CHXMemCacheObject::CHXMemCacheObject
 *
 *  Constructor
 */
CHXMemCacheObject::CHXMemCacheObject(IHXCommonClassFactory* /*IN*/  pClassFactory)
    : m_RefCount      (0),
      m_pMemResponse(NULL),
      m_pClassFactory(NULL),
      m_ulCapacity(0),
      m_lThreshold(50),
      m_ulUsedCapacity(0),
      m_pList(NULL),
      m_ulCurrentWriteOffset(0),
      m_pPendingAddBlock(NULL),
      m_bInAddBlockDone(FALSE),
      m_bInReadBlockDone(FALSE),
      m_pMutex(NULL),
      m_ulCurrentReadOffset(0)
{
    MLOG_HTTP("CHXMemCacheObject::CHXMemCacheObject()n");
    if(pClassFactory != NULL)
    {
        m_pClassFactory = pClassFactory;
        m_pClassFactory->AddRef();
    }
    m_pPendingReadInfo.ulOffset = 0;
    m_pPendingReadInfo.ulLength = 0;
    m_pPendingReadInfo.pBlock = NULL;
    
    m_pList = new CHXSimpleList;
    #if defined(THREADS_SUPPORTED) || defined(_UNIX_THREADS_SUPPORTED)
        HXMutex::MakeMutex(m_pMutex);
    #else
        HXMutex::MakeStubMutex(m_pMutex);
    #endif
}
/****************************************************************************
 *  CHXMemCacheObject::~CHXMemCacheObject
 *
 *  Destructor
 */
CHXMemCacheObject::~CHXMemCacheObject()
{
    MLOG_HTTP("CHXMemCacheObject::~CHXMemCacheObject()n");
    m_pMutex->Lock();
    // Destroy the list
    if(m_pList)
    {
        LISTPOSITION currPos = m_pList->GetHeadPosition();
        Info* currInfo;
        while(currPos != NULL)
        {
            currInfo = (Info *)m_pList->GetNext(currPos);
            currInfo->pBlock->Release();
            delete currInfo;
        }
        delete m_pList;
    }
    m_pMutex->Unlock();
    HX_DELETE(m_pMutex);
} // ~CHXMemCacheObject()
// IUnknown COM Interface Methods
/****************************************************************************
 *  IUnknown::AddRef
 *
 *  This routine increases the object reference count in a thread safe
 *  manner. The reference count is used to manage the lifetime of an object.
 *  This method must be explicitly called by the user whenever a new
 *  reference to an object is used.
 */
STDMETHODIMP_(UINT32) CHXMemCacheObject::AddRef(void)
{
    MLOG_HTTP("CHXMemCacheObject::AddRef()n");
    return InterlockedIncrement(&m_RefCount);
}
/****************************************************************************
 *  IUnknown::Release
 *
 *  This routine decreases the object reference count in a thread safe
 *  manner, and deletes the object if no more references to it exist. It must
 *  be called explicitly by the user whenever an object is no longer needed.
 */
STDMETHODIMP_(UINT32) CHXMemCacheObject::Release(void)
{
    MLOG_HTTP("CHXMemCacheObject::Release()n");
    if (InterlockedDecrement(&m_RefCount) > 0)
    {
	return m_RefCount;
    }
    delete this;
    return 0;
}
/****************************************************************************
 *  IUnknown::QueryInterface
 *
 *  This routine indicates which interfaces this object supports. If a given
 *  interface is supported, the object's reference count is incremented, and
 *  a reference to that interface is returned. Otherwise a NULL object and
 *  error code are returned. This method is called by other objects to
 *  discover the functionality of this object.
 */
STDMETHODIMP CHXMemCacheObject::QueryInterface(REFIID interfaceID,
					       void** ppInterfaceObj)
{
    MLOG_HTTP("CHXMemCacheObject::QueryInterface()n");
    // By definition all COM objects support the IUnknown interface
    if (IsEqualIID(interfaceID, IID_IUnknown))
    {
	AddRef();
	*ppInterfaceObj = (IUnknown*)(IHXCacheObject*)this;
	return HXR_OK;
    }
    // IHXCacheObject interface is supported
    else if (IsEqualIID(interfaceID, IID_IHXCacheObject))
    {
	AddRef();
	*ppInterfaceObj = (IHXCacheObject*)this;
	return HXR_OK;
    }
    // No other interfaces are supported
    *ppInterfaceObj = NULL;
    return HXR_NOINTERFACE;
}
//IHXCacheObject methods
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::Init
 *
 *	Purpose:
 *
 *	    Associates a cache object with the response object
 *	    it should notify of operation completeness.
 */
STDMETHODIMP
CHXMemCacheObject::Init(IHXCacheObjectResponse*     /*IN*/  pMemResponse,
                        UINT32                      /*IN*/  ulCapacity,
                        UINT32                      /*IN*/  lThreshold)
{
    MLOG_HTTP("CHXMemCacheObject::Init(Capacity = %u, Threshold = %d)n", ulCapacity, lThreshold);
    HX_RESULT res = HXR_OK;
    if(pMemResponse != NULL)
    {
        // Release any previous response objects
        if(m_pMemResponse != NULL)
        {
            m_pMemResponse->Release();
        }
        m_pMemResponse = pMemResponse;
        pMemResponse->AddRef();
    
    }
    else
    {
        res = HXR_INVALID_PARAMETER;
    }
    m_ulCapacity = ulCapacity;
    if( (lThreshold < 0) || (lThreshold >= 100) ) 
    {
        res = HXR_INVALID_PARAMETER;
    }
    else
    {
        m_lThreshold = lThreshold;
    }
    m_pMemResponse->InitDone(res);
    // HXR_OK from this function indicates InitDone() will be called.
    // Since this statement is executed only after the above InitDone()
    // we return HXR_OK instead of res. 
    return HXR_OK;
} // Init()
/************************************************************************
     *	Method:
     *
     *	    IHXCacheObject::GetThreshold
     *
     *	Purpose:
     *
     *	    Obtain the threshold of the cache object.
     */
STDMETHODIMP_(UINT32)
CHXMemCacheObject::GetThreshold(void)
{
    MLOG_HTTP("CHXFileCacheObject::GetThreshold()n"); 
    return m_lThreshold;
} // GetThreshold()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::ChangeThreshold
 *
 *	Purpose:
 *
 *	    The object keeps caching data until it is full (exhausts its 
 *      capacity). Once it is full, it will overwite existing cached data
 *      with new data ONLY if the percentage of cached data which has been
 *      read from the cache using the ReadBlock() method is *greater* than a
 *      given percentage of Capacity.. This percentage is set using the SetThreshold()
 *      method. In case the threshold is exceeded, the oldest added data
 *      (the data with the the least offset) will be discarded and the 
 *      amount of data discarded is so that the remaining cached data just
 *      satisfies the threshold condidtion (approximately).
 *
 *      This cache object is used in the HTTP/1.0 file system plugin for
 *      mobile devices and in this case, the threshold is set to 70%
 *      i.e., fNewThreshold = 0.7
 *
 */
STDMETHODIMP
CHXMemCacheObject::ChangeThreshold(UINT32  /*IN*/	lNewThreshold)
{
    MLOG_HTTP("CHXMemCacheObject::ChangeThreshold(%d)n", lNewThreshold); 
    if( (lNewThreshold < 0) || (lNewThreshold >= 100) )
    {
        return HXR_INVALID_PARAMETER;
    }
    m_pMutex->Lock();
    UINT32 lOldThreshold = m_lThreshold;
    m_lThreshold = lNewThreshold;
    HX_RESULT res = _CheckForThresholdCondition();
    if(HXR_OK != res)
    {
        // Revert back as something got messed up.
        m_lThreshold = lOldThreshold;
    }
    m_pMutex->Unlock();
    return res;
} // ChangeThreshold()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::GetCapacity
 *
 *	Purpose:
 *
 *	    Obtain the capacity in bytes of the cache object.
 */
STDMETHODIMP_(UINT32)
CHXMemCacheObject::GetCapacity(void)
{
    MLOG_HTTP("CHXMemCacheObject::GetCapacity()n"); 
    
    return m_ulCapacity;
} // GetCapacity()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::ChangeCapacity
 *
 *	Purpose:
 *
 *	    Change the capacity of the cache object.
 */
STDMETHODIMP
CHXMemCacheObject::ChangeCapacity(UINT32  /*IN*/	newByteCount) 
{
   MLOG_HTTP("CHXMemCacheObject::ChangeCapacity(%u)n", newByteCount); 
   HX_RESULT res = HXR_OK;
    
   m_pMutex->Lock();
   UINT32 ulOldCapacity = m_ulCapacity;
   m_ulCapacity = newByteCount;
   int ulExcessData = m_ulUsedCapacity - newByteCount;
   
   if(ulExcessData > 0)
   {
       // Discard the excess data.
       res = _DiscardData((UINT32)ulExcessData);
       if(HXR_OK != res)
       {
           // Revert back to old capacity if you couldn't
           // discard data.
           m_ulCapacity = ulOldCapacity;    
       }
       else
       {
           // Capacity has changed, so threshold might have been exceeded.
           res = _CheckForThresholdCondition();
       }
   }
   m_pMutex->Unlock();
   m_pMemResponse->ChangeCapacityDone(res);
   
   // HXR_OK from this function indicates ChangeCapacityDone() will be called.
   // Since this statement is executed only after the above ChangeCapacityDone()
   // we return HXR_OK instead of res. 
   return HXR_OK;
} // ChangeCapacity()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::GetUnusedCapacity
 *
 *	Purpose:
 *
 *	    Obtain the unused capacity in bytes of the cache object.
 */
STDMETHODIMP_(UINT32)
CHXMemCacheObject::GetUnusedCapacity()
{
    MLOG_HTTP("CHXMemCacheObject::GetUnusedCapacity()n");
    m_pMutex->Lock();
    UINT32 ulUnusedCapacity = m_ulCapacity - m_ulUsedCapacity;
    m_pMutex->Unlock();
    return ulUnusedCapacity;
} // GetUnusedCapacity()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::AddBlock
 *
 *	Purpose:
 *
 *	    Adds a block of data to the cache.
 */
STDMETHODIMP
CHXMemCacheObject::AddBlock(IHXBuffer*	/*IN*/	pBlock) 
{
    MLOG_HTTP("CHXMemCacheObject::AddBlock()n");
    if(pBlock == NULL)
    {
        return HXR_INVALID_PARAMETER;
    }
    if(m_pList == NULL)
        return HXR_UNEXPECTED;
            
    if(m_pPendingAddBlock != NULL)
    {
        return HXR_UNEXPECTED;
    }
    else
    {
        m_pPendingAddBlock = pBlock;
        m_pPendingAddBlock->AddRef();
    }
    if(!m_bInAddBlockDone)
    {
        while(m_pPendingAddBlock)
        {
            IHXBuffer* pTempBlock = m_pPendingAddBlock;
            m_pPendingAddBlock = NULL;
            UINT32 ulBlockSize = pTempBlock->GetSize();
            Info *pNewInfo = NULL;
            HX_RESULT res = HXR_OK;
            if(ulBlockSize != 0)
            {
                m_pMutex->Lock(); 
           
                // Can you accomodate this data?
                if(m_ulUsedCapacity + ulBlockSize > m_ulCapacity)
                {
                    res = HXR_OUTOFMEMORY;
                }
                else
                {
                    pNewInfo = new Info;
                    if(pNewInfo == NULL)
                        res = HXR_OUTOFMEMORY;
                }
                if(HXR_OK == res)
                {
                    // The new block should be contiguous
                    pNewInfo->ulOffset = m_ulCurrentWriteOffset;
                    pNewInfo->ulSize = ulBlockSize;
                    pNewInfo->pBlock = pTempBlock;
                    m_ulUsedCapacity += ulBlockSize;
                    m_ulCurrentWriteOffset += ulBlockSize;
                    m_pList->AddTail( (void *)pNewInfo );
                }
            
                m_pMutex->Unlock();
            }
            else
            {
                pTempBlock->Release();
            }
            m_bInAddBlockDone = TRUE;
            m_pMemResponse->AddBlockDone(res);
            m_bInAddBlockDone = FALSE;
        } // while
    }
    return HXR_OK;
} // AddBlock()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::VerifyBlock
 *
 *	Purpose:
 *
 *	    Verify that a block of data is in the cache.
 */
STDMETHODIMP
CHXMemCacheObject::VerifyBlock(UINT32	/*IN*/	ulBlockOffset,
			 UINT32	/*IN*/	ulBlockLength)
{
    MLOG_HTTP("CHXMemCacheObject::VeifyBlock()n");
    if(m_pList == NULL)
        return HXR_UNEXPECTED;
    m_pMutex->Lock();
    
    // Critical Section starts
    BOOL bExists = TRUE;
    if(m_ulUsedCapacity == 0)
    {
        bExists = FALSE;
    }
    else
    {
        UINT32 ulLeastOffset = m_ulCurrentWriteOffset - m_ulUsedCapacity;
        UINT32 ulHighestOffset = m_ulCurrentWriteOffset - 1;
        
        BOOL bStartExists = (ulBlockOffset >= ulLeastOffset) && 
                            (ulBlockOffset <= ulHighestOffset);
        BOOL bEndExists = (ulBlockOffset + ulBlockLength - 1 >= ulLeastOffset) &&
                          (ulBlockOffset + ulBlockLength - 1 <= ulHighestOffset);
        bExists = bStartExists && bEndExists;
    }
    // Critical section ends
    m_pMutex->Unlock();
    m_pMemResponse->VerifyBlockDone(bExists);
    return HXR_OK;
} // VerifyBlock()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::ReadBlock
 *
 *	Purpose:
 *
 *	    Read a block out of the cache.
 */
STDMETHODIMP
CHXMemCacheObject::ReadBlock(UINT32	/*IN*/	ulBlockOffset,
		            UINT32	/*IN*/	ulBlockLength)
{
    MLOG_HTTP("CHXMemCacheObject::ReadBlock(Offset = %u, Length = %u)n", ulBlockOffset, ulBlockLength);
    if(m_pList == NULL)
        return HXR_UNEXPECTED;
    if(m_pPendingReadInfo.pBlock != NULL)
        return HXR_UNEXPECTED;
    m_pClassFactory->CreateInstance(CLSID_IHXBuffer,
                     (void **) &m_pPendingReadInfo.pBlock);
    if(m_pPendingReadInfo.pBlock == NULL)
        return HXR_OUTOFMEMORY;
    HX_RESULT res = m_pPendingReadInfo.pBlock->SetSize(ulBlockLength);
    if(res != HXR_OK)
    {
        m_pPendingReadInfo.pBlock->Release();
        m_pPendingReadInfo.pBlock = NULL;
        return res;
    }
    m_pPendingReadInfo.ulLength = ulBlockLength;
    m_pPendingReadInfo.ulOffset = ulBlockOffset;
    if(!m_bInReadBlockDone)
    {
        while(m_pPendingReadInfo.pBlock)
        {
            HX_RESULT res2 = HXR_OK;
            // To prepare for the possibilty of ReadBlock()
            // being called from ReadBlockDone()
            IHXBuffer* pTempBlock = m_pPendingReadInfo.pBlock;
            m_pPendingReadInfo.pBlock = NULL;
            UINT32 ulTempLength = m_pPendingReadInfo.ulLength;
            m_pPendingReadInfo.ulLength = 0;
            UINT32 ulTempOffset = m_pPendingReadInfo.ulOffset;
            m_pPendingReadInfo.ulOffset = 0;
            m_pMutex->Lock();
            UINT32 ulLeastOffset = m_ulCurrentWriteOffset - m_ulUsedCapacity; 
            UINT32 ulHighestOffset = m_ulCurrentWriteOffset - 1;
            if(m_ulUsedCapacity == 0)
            {
                if(ulTempOffset >= m_ulCurrentWriteOffset)
                    res2 = HXR_INCOMPLETE;
                else
                    res2 = HXR_FAIL;
                    
                HX_RELEASE(pTempBlock);
                pTempBlock = NULL;
            }
            else if(ulTempOffset < ulLeastOffset)
            {
                res2 = HXR_FAIL;
                HX_RELEASE(pTempBlock);
                pTempBlock = NULL;
            }
            else if(ulTempOffset > ulHighestOffset)
            {
                res2 = HXR_INCOMPLETE;
                HX_RELEASE(pTempBlock);
                pTempBlock = NULL;
                // If 'forward data' requested, mark all data as read so
                // that old data can be discarded to make space for new data.
                //m_ulCurrentReadOffset = ulHighestOffset + 1; 
                m_ulCurrentReadOffset = ulTempOffset;
                _CheckForThresholdCondition();
            }
            else
            {
                // Fill the pTempBlock with data from the list
            
                UCHAR* ucTempBlockData = pTempBlock->GetBuffer();
                UINT32 ulBytesReadFromList = 0;
                LISTPOSITION currPos = m_pList->GetHeadPosition();
                Info* currInfo;
                while(currPos != NULL)
                {   
                    currInfo = (Info *)m_pList->GetNext(currPos);
                    UINT32 ulCurrLowOffset = currInfo->ulOffset;
                    UINT32 ulCurrHighOffset = currInfo->ulOffset + currInfo->ulSize - 1;
                    UCHAR* ucCurrBlockData = currInfo->pBlock->GetBuffer();
                    if( (ulTempOffset >= ulCurrLowOffset) && (ulTempOffset <= ulCurrHighOffset) )
                    {
                        UINT32 ulMatchSize = ( (ulCurrHighOffset - ulTempOffset + 1) < ulTempLength ) ?
                                                ulCurrHighOffset - ulTempOffset + 1 : ulTempLength;
                        memcpy((void*)(ucTempBlockData + ulBytesReadFromList),
                                (void*)(ucCurrBlockData + ulTempOffset - ulCurrLowOffset), ulMatchSize);
                        ulBytesReadFromList += ulMatchSize;
                        ulTempOffset += ulMatchSize;
                        ulTempLength -= ulMatchSize;
                        if(0 == ulTempLength)
                            break;
                    }
                }
                if(ulTempLength > 0)
                {
                    res2 = HXR_INCOMPLETE;
                    pTempBlock->SetSize(ulBytesReadFromList);   
                }
                else
                {
                    res2 = HXR_OK;
                }
                m_ulCurrentReadOffset = ulTempOffset;
                _CheckForThresholdCondition();
            }
            m_pMutex->Unlock();
            m_bInReadBlockDone = TRUE;
            m_pMemResponse->ReadBlockDone(res2, pTempBlock);
            m_bInReadBlockDone = FALSE;
            
            HX_RELEASE(pTempBlock);
        }
    }
    return HXR_OK;
} // ReadBlock()
/************************************************************************
 *	Method:
 *	    IHXCacheObject::Flush
 *
 *	Purpose:
 *
 *	    Releases all data buffers cached in the object. The object now
 *      gets to a same state as when it was newly created. After flushine,
 *	    the object can be used for reading/writing as before.
 */
STDMETHODIMP
CHXMemCacheObject::Flush(void) 
{
    MLOG_HTTP("CHXMemCacheObject::Flush()n");
    if(!m_pList)
        return HXR_UNEXPECTED;;
    
    m_pMutex->Lock();
    LISTPOSITION currPos = m_pList->GetHeadPosition();
    Info* currInfo;
    while(currPos != NULL)
    {
        currInfo = (Info *)m_pList->GetNext(currPos);
        currInfo->pBlock->Release();
        delete currInfo;
    }
    m_pList->RemoveAll();
    m_ulUsedCapacity = 0;
    m_ulCurrentWriteOffset = 0;
    m_ulCurrentReadOffset = 0;
    m_pMutex->Unlock();
    m_pMemResponse->FlushDone(HXR_OK);
    return HXR_OK;
} // Flush()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::IsFull
 *
 *	Purpose:
 *
 *	    Can the cache object accept any more data for storage?
 */
STDMETHODIMP_(BOOL)
CHXMemCacheObject::IsFull()
{
    MLOG_HTTP("CHXMemCacheObject::IsFull()n");
    m_pMutex->Lock();
    BOOL bIsFull = TRUE;
    if(m_ulUsedCapacity < m_ulCapacity)
        bIsFull = FALSE;
    
    m_pMutex->Unlock();
    return bIsFull;
} // IsFull()
/************************************************************************
 *	Method:
 *
 *	    IHXCacheObject::IsEmpty
 *
 *	Purpose:
 *
 *	    Does the cache object have any data stored?
 */
STDMETHODIMP_(BOOL)
CHXMemCacheObject::IsEmpty()
{
    MLOG_HTTP("CHXMemCacheObject::IsEmpty()n");
    if(m_ulUsedCapacity == 0)
        return TRUE;
    else
        return FALSE;
} // IsEmpty()
// Discards exactly 'byteCount' amount of oldest data.
// Note that this method is not thread safe. The caller has to take 
// care of locking common data structures before calling this method.
HX_RESULT CHXMemCacheObject::_DiscardData(UINT32 byteCount)
{
    MLOG_HTTP("CHXMemCacheObject::_DiscardData(%u)n", byteCount);
    HX_RESULT res = HXR_UNEXPECTED;
    UINT32 ulDiscardedData = 0;
    LISTPOSITION currHeadPos = NULL;
    Info *headInfo = NULL;
    while( (currHeadPos = m_pList->GetHeadPosition())!= NULL )
    {
        headInfo = (Info*)(m_pList->RemoveHead());
        UINT32 ulHeadBlockSize = headInfo->ulSize;
        if(ulDiscardedData + ulHeadBlockSize <= byteCount)
        {
            headInfo->pBlock->Release();
            delete headInfo;
            
            ulDiscardedData += ulHeadBlockSize;
        }
        else
        {
            if(ulDiscardedData + ulHeadBlockSize > byteCount)
            {
                UINT32 ulValidDataSize = (ulDiscardedData + ulHeadBlockSize - byteCount);
                UINT32 ulInvalidDataSize = ulHeadBlockSize - ulValidDataSize;
                Info *pNewInfo = new Info;
                if(pNewInfo == NULL)
                {
                   res = HXR_OUTOFMEMORY;
                   break;
                }
                m_pClassFactory->CreateInstance(CLSID_IHXBuffer,
                                               (void **) &(pNewInfo->pBlock));
                if(pNewInfo->pBlock == NULL)
                    break;
                res = pNewInfo->pBlock->SetSize(ulValidDataSize);
                if(res != HXR_OK)
                    break;
                memcpy( (void*)(pNewInfo->pBlock->GetBuffer()),
                        (void*)(headInfo->pBlock->GetBuffer()+ ulInvalidDataSize),
                        ulValidDataSize );
                pNewInfo->ulOffset = headInfo->ulOffset + ulInvalidDataSize;
                pNewInfo->ulSize = ulValidDataSize;
                m_pList->AddHead( (void *)pNewInfo );
                headInfo->pBlock->Release();
                delete headInfo;
            }
            ulDiscardedData = byteCount;
            headInfo = NULL;
            res = HXR_OK;
            break;
        }
    }
    m_ulUsedCapacity -= ulDiscardedData;
    return res;
}
// Check if utilizedData has exceeded THRESHOLD. If yes, discard 
// appropriate amount of data. Note that this
// method is not thread safe. The caller has to take care of 
// locking common data structures before calling this method.
HX_RESULT CHXMemCacheObject::_CheckForThresholdCondition()
{
    MLOG_HTTP("CHXMemCacheObject::_CheckForThresholdCondition()n");
    if(m_ulUsedCapacity == 0)
    {
        return HXR_OK;
    }
    UINT32 ulLeastOffset = m_ulCurrentWriteOffset - m_ulUsedCapacity;
    UINT32 ulHighestOffset = m_ulCurrentWriteOffset - 1;
    HX_RESULT res = HXR_OK;
    INT32 ulExcess = (m_ulCurrentReadOffset - ulLeastOffset) - 
                      (INT32)(m_lThreshold * m_ulCapacity * 0.01);
    if(ulExcess > 0)
    {
        if(ulExcess > m_ulUsedCapacity)
            ulExcess = m_ulUsedCapacity; 
        res = _DiscardData(ulExcess);
    }
    return res;
} // _CheckForThresholdCondition()

						