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BUG#: 5314
TITLE: IPC Refactoring

DESCRIPTION: This patch cleans up the IPC related classes. It (1) reorganizes
related classes into their own headers, (2) makes the mutex class recursive to
eliminate recursive lock exclusion logic, (3) reimplements condition variables,
renames dozens of global functions.

//%2006////////////////////////////////////////////////////////////////////////
//
// Copyright (c) 2000, 2001, 2002 BMC Software; Hewlett-Packard Development
// Company, L.P.; IBM Corp.; The Open Group; Tivoli Systems.
// Copyright (c) 2003 BMC Software; Hewlett-Packard Development Company, L.P.;
// IBM Corp.; EMC Corporation, The Open Group.
// Copyright (c) 2004 BMC Software; Hewlett-Packard Development Company, L.P.;
// IBM Corp.; EMC Corporation; VERITAS Software Corporation; The Open Group.
// Copyright (c) 2005 Hewlett-Packard Development Company, L.P.; IBM Corp.;
// EMC Corporation; VERITAS Software Corporation; The Open Group.
// Copyright (c) 2006 Hewlett-Packard Development Company, L.P.; IBM Corp.;
// EMC Corporation; Symantec Corporation; The Open Group.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to
// deal in the Software without restriction, including without limitation the
// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
// sell copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
// 
// THE ABOVE COPYRIGHT NOTICE AND THIS PERMISSION NOTICE SHALL BE INCLUDED IN
// ALL COPIES OR SUBSTANTIAL PORTIONS OF THE SOFTWARE. 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 AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
// ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//
//==============================================================================
//
// Author: Mike Brasher, Inova Europe (mbrasher@bmc.com)
//
//%/////////////////////////////////////////////////////////////////////////////

#ifndef PegasusRepository_ObjectCache_h
#define PegasusRepository_ObjectCache_h

#include <Pegasus/Common/Config.h>
#include <Pegasus/Common/CIMClass.h>
#include <Pegasus/Common/CIMInstance.h>
#include <Pegasus/Common/HashTable.h>
#include <Pegasus/Common/Mutex.h>
#include <Pegasus/Repository/Linkage.h>

PEGASUS_NAMESPACE_BEGIN

Uint32 ObjectCacheHash(const String& str);

template<class OBJECT>
class PEGASUS_REPOSITORY_LINKAGE ObjectCache
{
public:

    ObjectCache(size_t maxEntries);

    void put(const String& path, OBJECT& object);

    bool get(const String& path, OBJECT& object);

    bool evict(const String& path);

#ifdef PEGASUS_DEBUG
    void DisplayCacheStatistics(void)
    {
        PEGASUS_STD(cout) << "  Size (current/max): " << _numEntries <<
            "/" << _maxEntries << PEGASUS_STD(endl);
        PEGASUS_STD(cout) << "  Requests satisfied from cache: " <<
            _cacheReadHit << PEGASUS_STD(endl);
        PEGASUS_STD(cout) << "  Requests *not* satisfied from cache: " <<
            _cacheReadMiss << " (implies write to cache)" << PEGASUS_STD(endl);
        PEGASUS_STD(cout) <<
            "  Cache entries \"aged out\" due to cache size constraints: " <<
            _cacheRemoveLRU << PEGASUS_STD(endl);
    }
#endif


private:

    static Uint32 _hash(const String& s)
    {
	return ObjectCacheHash(s);
    }

    static bool _equal(const String& s1, const String& s2)
    {
        return String::equalNoCase(s1, s2);
    }

    struct Entry
    {
	Uint32 code;
	String path;
	OBJECT object;
	Entry* hashNext;
	Entry* queueNext;
	Entry* queuePrev;

	Entry(Uint32 code_, const String& path_, OBJECT& object_) :
	    code(code_), path(path_), object(object_.clone()) { }
    };

    enum { NUM_CHAINS = 128 };

    Entry* _chains[NUM_CHAINS];
    Entry* _front;
    Entry* _back;
    size_t _numEntries;
    size_t _maxEntries;
    Mutex _mutex;

#ifdef PEGASUS_DEBUG
    Uint32 _cacheReadHit;
    Uint32 _cacheReadMiss;
    Uint32 _cacheRemoveLRU;
#endif


};

template<class OBJECT>
ObjectCache<OBJECT>::ObjectCache(size_t maxEntries) : 
    _front(0), _back(0), _numEntries(0), _maxEntries(maxEntries)
#ifdef PEGASUS_DEBUG
    , _cacheReadHit(0), _cacheReadMiss(0), _cacheRemoveLRU(0)
#endif
{
    memset(_chains, 0, sizeof(_chains));
}

template<class OBJECT>
void ObjectCache<OBJECT>::put(const String& path, OBJECT& object)
{
    if (_maxEntries == 0)
	return;

    _mutex.lock();

    //// Update object if it is already in cache:

    Uint32 code = _hash(path);
    Uint32 index = code % NUM_CHAINS;

    for (Entry* p = _chains[index]; p; p = p->hashNext)
    {
        if (code == p->code && _equal(p->path, path))
	{
	    // Update the repository.
	    p->object = object.clone();
	    _mutex.unlock();
	    return;
	}
    }

    //// Add to hash table:

    Entry* entry = new Entry(code, path, object);
    entry->hashNext = _chains[index];
    _chains[index] = entry;

    //// Add to back of FIFO queue:

    entry->queueNext = 0;

    if (_back)
    {
	_back->queueNext = entry;
	entry->queuePrev = _back;
	_back = entry;
    }
    else
    {
	_front = entry;
	_back = entry;
	entry->queuePrev = 0;
    }

    _numEntries++;

    //// Evict LRU entry if necessary (from front).

    if (_numEntries > _maxEntries)
    {
	Entry* entry = _front;

	//// Remove from hash table first.

	Uint32 index = entry->code % NUM_CHAINS;
	Entry* hashPrev = 0;

	for (Entry* p = _chains[index]; p; p = p->hashNext)
	{
	    if (p->code == entry->code && _equal(p->path, entry->path))
	    {
		if (hashPrev)
		    hashPrev->hashNext = p->hashNext;
		else
		    _chains[index] = p->hashNext;

		break;
	    }

	    hashPrev = p;
	}

	//// Now remove from queue:

	_front = entry->queueNext;

	if (_front)
	    _front->queuePrev = 0;

	delete entry;
	_numEntries--;
#ifdef PEGASUS_DEBUG
    _cacheRemoveLRU++;
#endif
    }

    _mutex.unlock();
    return;
}

template<class OBJECT>
bool ObjectCache<OBJECT>::get(const String& path, OBJECT& object)
{
    if (_maxEntries == 0)
	return false;

    _mutex.lock();

    //// Search cache for object.

    Uint32 code = _hash(path);
    Uint32 index = code % NUM_CHAINS;

    for (Entry* p = _chains[index]; p; p = p->hashNext)
    {
        if (code == p->code && _equal(p->path, path))
	{
	    object = p->object.clone();
#ifdef PEGASUS_DEBUG
        _cacheReadHit++;
#endif
	    _mutex.unlock();
	    return true;
	}
    }

    /// Not found!

#ifdef PEGASUS_DEBUG
    _cacheReadMiss++;
#endif
    _mutex.unlock();
    return false;
}

template<class OBJECT>
bool ObjectCache<OBJECT>::evict(const String& path)
{
    if (_maxEntries == 0)
	return false;

    _mutex.lock();

    //// Find and remove the given element.

    Uint32 code = _hash(path);
    Uint32 index = code % NUM_CHAINS;
    Entry* hashPrev = 0;

    for (Entry* p = _chains[index]; p; p = p->hashNext)
    {
        if (code == p->code && _equal(p->path, path))
	{
	    // Remove from hash chain:

            if (hashPrev)
                hashPrev->hashNext = p->hashNext;
            else
                _chains[index] = p->hashNext;

	    // Remove from queue:

	    if (p->queuePrev)
		p->queuePrev->queueNext = p->queueNext;
	    else
		_front = p->queueNext;

	    if (p->queueNext)
		p->queueNext->queuePrev = p->queuePrev;
	    else
		_back = p->queuePrev;

	    // Delete the entry and update the number of entries.

	    delete p;
	    _numEntries--;

	    _mutex.unlock();
	    return true;
	}

	hashPrev = p;
    }

    //// Not found!

    _mutex.unlock();
    return false;
}

PEGASUS_NAMESPACE_END

#endif /* PegasusRepository_ObjectCache_h */