greenplumn CCacheAccessor 源码

greenplumn CCacheAccessor 代码

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

//---------------------------------------------------------------------------
//	Greenplum Database
//	Copyright (C) 2011 EMC CORP.
//
//	@filename:
//		CCacheAccessor.h
//
//	@doc:
//		Definition of cache accessor base class.
//.
//	@owner:
//
//	@test:
//
//---------------------------------------------------------------------------
#ifndef GPOS_CCACHEACCESSOR_H_
#define GPOS_CCACHEACCESSOR_H_

#include "gpos/base.h"
#include "gpos/memory/CCache.h"

using namespace gpos;

namespace gpos
{
//---------------------------------------------------------------------------
//	@class:
//		CCacheAccessor
//
//	@doc:
//		Definition of CCacheAccessor;
//
//		The accessor holds exactly one cached object at a time.
//
//		The accessor's API includes four main functions:
//			(1) Inserting a new object in the cache
//			(2) Looking up a cached object by key
//			(3) Deleting a cached object
//			(4) Iterating over cached objects with the same key
//---------------------------------------------------------------------------
template <class T, class K>
class CCacheAccessor
{
private:
	// the underlying cache
	CCache<T, K> *m_cache;

	// memory pool of a cached object inserted by the accessor
	CMemoryPool *m_mp;

	// cached object currently held by the accessor
	typename CCache<T, K>::CCacheHashTableEntry *m_entry;

	// true if insertion of a new object into the cache was successful
	BOOL m_inserted;

public:
	// ctor; protected to disable instantiation unless from child class
	CCacheAccessor(CCache<T, K> *cache)
		: m_cache(cache), m_mp(nullptr), m_entry(nullptr), m_inserted(false)

	{
		GPOS_ASSERT(nullptr != cache);
	}

	// dtor
	~CCacheAccessor()
	{
		// check if a memory pool was created but insertion failed
		if (nullptr != m_mp && !m_inserted)
		{
			CMemoryPoolManager::GetMemoryPoolMgr()->Destroy(m_mp);
		}

		// release entry if one was created
		if (nullptr != m_entry)
		{
			m_cache->ReleaseEntry(m_entry);
		}
	}

	// the following functions are hidden since they involve
	// (void *) key/value data types; the actual types are defined
	// as template parameters in the child class CCacheAccessor

	// inserts a new object into the cache
	T
	Insert(K key, T val)
	{
		GPOS_ASSERT(nullptr != m_mp);

		GPOS_ASSERT(!m_inserted && "Accessor was already used for insertion");

		GPOS_ASSERT(nullptr == m_entry && "Accessor already holds an entry");

		CCacheEntry<T, K> *entry = GPOS_NEW(m_cache->m_mp)
			CCacheEntry<T, K>(m_mp, key, val, m_cache->m_gclock_init_counter);

		CCacheEntry<T, K> *ret = m_cache->InsertEntry(entry);

		// check if insertion completed successfully
		if (entry == ret)
		{
			m_inserted = true;
		}
		else
		{
			GPOS_DELETE(entry);
		}

		// accessor holds the returned entry in all cases
		m_entry = ret;

		return ret->Val();
	}

	// returns the object currently held by the accessor
	T
	Val() const
	{
		T ret = NULL;
		if (nullptr != m_entry)
		{
			ret = m_entry->Val();
		}

		return ret;
	}

	// gets the next undeleted object with the same key
	T
	Next()
	{
		GPOS_ASSERT(nullptr != m_entry);

		typename CCache<T, K>::CCacheHashTableEntry *entry = m_entry;
		m_entry = m_cache->Next(m_entry);

		// release previous entry
		m_cache->ReleaseEntry(entry);

		return Val();
	}

public:
	// creates a new memory pool for allocating a new object
	CMemoryPool *
	Pmp()
	{
		GPOS_ASSERT(nullptr == m_mp);

		// construct a memory pool for cache entry
		m_mp = CMemoryPoolManager::GetMemoryPoolMgr()->CreateMemoryPool();

		return m_mp;
	}

	// finds the first object matching the given key
	void
	Lookup(K key)
	{
		GPOS_ASSERT(nullptr == m_entry && "Accessor already holds an entry");

		m_entry = m_cache->Get(key);

		if (nullptr != m_entry)
		{
			// increase ref count before return the object to the customer
			// customer is responsible for decreasing the ref count after use
			m_entry->IncRefCount();
		}
	}

	// marks currently held object as deleted
	void
	MarkForDeletion()
	{
		GPOS_ASSERT(nullptr != m_entry);

		m_entry->MarkForDeletion();
	}

};	// CCacheAccessor

}  //namespace gpos

#endif	// GPOS_CCACHEACCESSOR_H_

// EOF

相关信息

greenplumn 源码目录

相关文章

greenplumn CAutoMemoryPool 源码

greenplumn CCache 源码

greenplumn CCacheEntry 源码

greenplumn CCacheFactory 源码

greenplumn CMemoryPool 源码

greenplumn CMemoryPoolManager 源码

greenplumn CMemoryPoolStatistics 源码

greenplumn CMemoryPoolTracker 源码

greenplumn CMemoryVisitorPrint 源码

greenplumn IMemoryVisitor 源码