greenplumn CCacheEntry 源码

greenplumn CCacheEntry 代码

文件路径：/src/backend/gporca/libgpos/include/gpos/memory/CCacheEntry.h

//---------------------------------------------------------------------------
//	Greenplum Database
//	Copyright (C) 2011 EMC Corp.
//
//	@filename:
//		CCacheEntry.h
//
//	@doc:
//		Definition of cache class.
//.
//	@owner:
//
//	@test:
//
//---------------------------------------------------------------------------
#ifndef GPOS_CCACHEENTRY_H_
#define GPOS_CCACHEENTRY_H_

#include "gpos/common/CList.h"
#include "gpos/memory/CMemoryPool.h"


// setting the cache quota to 0 means unlimited
#define UNLIMITED_CACHE_QUOTA 0

// no. of hashtable buckets
#define CACHE_HT_NUM_OF_BUCKETS 1000

using namespace gpos;

namespace gpos
{
//---------------------------------------------------------------------------
//	@class:
//		CCacheEntry
//
//	@doc:
//		Definition of cache entry;
//
//		Each cache entry is a container that holds information about one
//		cached object.
//
//---------------------------------------------------------------------------
template <class T, class K>
class CCacheEntry
{
private:
	// allocated memory pool to the cached object
	CMemoryPool *m_mp;

	// value that needs to be cached
	T m_val;

	// true if this entry is marked for deletion
	BOOL m_deleted;

	// gclock counter; an entry is eligible for eviction if this
	// counter drops to 0 and the entry is not pinned
	ULONG m_g_clock_counter;

public:
	// ctor
	CCacheEntry(CMemoryPool *mp, K key, T val, ULONG g_clock_counter)
		: m_mp(mp),
		  m_val(val),
		  m_deleted(false),
		  m_g_clock_counter(g_clock_counter),
		  m_key(key)
	{
		// CCache entry has the ownership now. So ideally any time ref count can't go lesser than 1.
		// In destructor, we decrease it from 1 to 0.
		IncRefCount();
	}

	// dtor
	virtual ~CCacheEntry()
	{
		// Decrease ref count of m_stats_comp_val_int to get destroyed by itself if ref count is 0
		DecRefCount();
	}

	// gets the key of cached object
	K
	Key() const
	{
		return m_key;
	}

	// gets the value of cached object
	T
	Val() const
	{
		return m_val;
	}

	// gets the memory pool of cached object
	CMemoryPool *
	Pmp() const
	{
		return m_mp;
	}

	// marks entry as deleted
	void
	MarkForDeletion()
	{
		m_deleted = true;
	}

	// returns true if entry is marked as deleted
	BOOL
	IsMarkedForDeletion() const
	{
		return m_deleted;
	}

	// get value's ref-count
	ULONG
	RefCount() const
	{
		return (ULONG) m_val->RefCount();
	}

	// increments value's ref-count
	void
	IncRefCount()
	{
		m_val->AddRef();
	}

	//decrements value's ref-count
	void
	DecRefCount()
	{
		m_val->Release();
	}

	// sets the gclock counter for an entry; useful for updating counter upon access
	void
	SetGClockCounter(ULONG g_clock_counter)
	{
		m_g_clock_counter = g_clock_counter;
	}

	// decrements the gclock counter for an entry during eviction process
	void
	DecrementGClockCounter()
	{
		m_g_clock_counter--;
	}

	// returns the current value of the gclock counter
	ULONG
	GetGClockCounter()
	{
		return m_g_clock_counter;
	}

	// the following data members are public because they
	// need to be used by GPOS_OFFSET macro for list construction

	// a pointer to entry's key
	K m_key;

	// link used to maintain entries in a hashtable
	SLink m_link_hash;

	// invalid key
	static const K m_invalid_key;

};	// CCacheEntry

}  // namespace gpos

#endif	// GPOS_CCACHEENTRY_H_

// EOF

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