gStore/VSTree/LRUCache.cpp

/*
* LRUCache.cpp
*
*  Created on: 2014-6-30
*      Author: hanshuo
*/

#include "LRUCache.h"
#include "VNode.h"

using namespace std;

//NOTICE: we aim to support 1 billion triples in a single machine, whose entity num
//can not exceed the 2 billion limit, and the maxium VNODE num is 2000000000/100=20000000=20M
//However, if there is really 20M VNODEs, the whole memory can not afford it!
//NOTICE:In fact, real graph is not linear, we can assume that 1 billion triples contains at most 1 billion entities
//then the memory cost at most is 23448 * 10M = 200G, which is also too large
//But we can only see at most 200M entities in web graphs, then the memory cost is 40G, which is affordable
//
//CONSIDER:support memory-disk swap in vstree
//However, if we adjust the sig length according to entity num, and VNODE size is decided by sig length, we can control the
//whole vstree memory cost almost 20G  
//What is more, if the system memory is enough(precisely, the memory you want to assign to gstore), 
//we can also set the sig length larger(which should be included in config file)
//int LRUCache::DEFAULT_CAPACITY = 10000000;
int LRUCache::DEFAULT_CAPACITY = 1 * 1000 * 1000;  //about 20G memory for vstree
//int LRUCache::DEFAULT_CAPACITY = 1000;
//TODO:10^6 is a good parameter, at most use 20G

LRUCache::LRUCache(int _capacity)
{
	//initialize the lock
#ifdef THREAD_ON
	pthread_rwlock_init(&(this->cache_lock), NULL);
#endif

	//cout<<"size of VNODE: "<<sizeof(VNode)<<endl;
	cout<<"size of VNODE: "<<VNode::VNODE_SIZE<<endl;
	cout << "LRUCache initial..." << endl;
	this->capacity = _capacity > 0 ? _capacity : LRUCache::DEFAULT_CAPACITY;

	// TODO+DEBUG:it seems that a minium size is required, for example, multiple path down(the height?)
	//at least 3*h
	//
	// we should guarantee the cache is big enough.
	//this->capacity = std::max(this->capacity, VNode::MAX_CHILD_NUM * 2000);

	this->next = new int[this->capacity + 2];
	this->prev = new int[this->capacity + 2];

	//for keys and values, each time we remove one ,we will fill one in the exact position
	//(each VNODE is the same size, so swap just one can be ok)
	//(if needing to remove, then we should move the last one to here)
	this->keys = new int[this->capacity + 2];
	this->values = new VNode*[this->capacity + 2];

	for (int i = 0; i < this->capacity + 2; ++i)
	{
		this->values[i] = NULL;
	}

	//prev and next are used to implement the LRU strategy
	this->next[LRUCache::START_INDEX] = LRUCache::END_INDEX;
	this->next[LRUCache::END_INDEX] = LRUCache::NULL_INDEX;
	this->prev[LRUCache::START_INDEX] = LRUCache::NULL_INDEX;
	this->prev[LRUCache::END_INDEX] = LRUCache::START_INDEX;
	this->size = 0;
	cout << "LRUCache initial finish" << endl;
}

LRUCache::~LRUCache()
{
	delete[] this->next;
	delete[] this->prev;
	delete[] this->keys;
	for (int i = 0; i < this->size; ++i)
	{
		delete this->values[i];
	}
	delete[] this->values;

	//destroy the lock
#ifdef THREAD_ON
	pthread_rwlock_destroy(&(this->cache_lock));
#endif
}

//NOTICE:this must be done in one thread(and only one time)
//load cache's elements from an exist data file. 
bool LRUCache::loadCache(string _filePath)
{
	this->dataFilePath = _filePath;

	FILE* filePtr = fopen(this->dataFilePath.c_str(), "rb");
	if (filePtr == NULL)
	{
		cerr << "error, can not load an exist data file. @LRUCache::loadCache" << endl;
		return false;
	}

	//NOTICE:here we set it to the maxium, to ensure all VNODE in memory
	int defaultLoadSize = this->capacity;
	//int defaultLoadSize = this->capacity / 2;
	size_t vNodeSize = VNode::VNODE_SIZE;
	//size_t vNodeSize = sizeof(VNode);
	int flag = 0;

	flag = fseek(filePtr, 0, SEEK_SET);

	if (flag != 0)
	{
		cerr << "error,can't seek to the fileLine. @LRUCache::loadCache" << endl;
		return false;
	}

	//int _tmp_cycle_count = 0;

	while (this->size < defaultLoadSize)
	{
		bool is_reach_EOF = feof(filePtr);
		if(is_reach_EOF)
		{
			break;
		}

		VNode* nodePtr = new VNode(true);
		//VNode* nodePtr = NULL;
		//bool is_node_read = (fread((char *)nodePtr, vNodeSize, 1, filePtr) == 1);
		bool is_node_read = nodePtr->readNode(filePtr);

		if (!is_node_read)
		{
			delete nodePtr;
			break;
		}

		//NOTICE:not consider invalid node
		if(nodePtr->getFileLine() < 0)
		{
			//remove invalid node
			delete nodePtr;
			continue;
		}

		//this->size if the real size, while DEFAULT_NUM is the prefix
		//To maintain a double-linked list, the pos 0 is head, while the pos 1 is tail
		int pos = LRUCache::DEFAULT_NUM + this->size;
		this->setElem(pos, nodePtr->getFileLine(), nodePtr);

		//debug
		//{
			//if (_tmp_cycle_count != nodePtr->getFileLine())
			//{
				//stringstream _ss;
				//_ss << "error file line: " << _tmp_cycle_count << " " << nodePtr->getFileLine() << " " << nodePtr->getChildNum() << endl;
				//Util::logging(_ss.str());
			//}
		//}

		//_tmp_cycle_count++;
	}

	fclose(filePtr);

	return true;
}

//create a new empty data file, the original one will be overwrite. 
bool LRUCache::createCache(string _filePath)
{
	this->dataFilePath = _filePath;

	FILE* filePtr = fopen(this->dataFilePath.c_str(), "wb");
	if (filePtr == NULL)
	{
		cerr << "error, can not create a new data file. @LRUCache::createCache" << endl;
		return false;
	}
	fclose(filePtr);

	return true;
}

//DEBUG+WARN:the memory-disk swap strategy exists serious bugs, however, we do not really use this startegy now!!!
//
//set the key(node's file line) and value(node's pointer). if the key exists now, the value of this key will be overwritten. 
bool LRUCache::set(int _key, VNode * _value)
{
#ifdef THREAD_ON
	pthread_rwlock_wrlock(&(this->cache_lock));
	pthread_mutex_lock(&(_value->node_lock));
#endif

	map<int, int>::iterator iter = this->key2pos.find(_key);

	// if the _key is found, overwrite its mapping value.
	if (iter != this->key2pos.end())
	{
		int pos = iter->second;
		this->freeElem(pos);
		this->setElem(pos, _key, _value);
		//this->refresh(pos);
	}
	// if the cache is not full now, just put the key-value to the free slot.
	else if (this->size < this->capacity)
	{
#ifdef DEBUG_LRUCACHE
		//cout<<"to insert a node in LRU cache"<<endl;
#endif
		int pos = LRUCache::DEFAULT_NUM + this->size;
		this->setElem(pos, _key, _value);
		//this->refresh(pos);
	}
	// if the cache is full, should swap out the least recently used one to hard disk.
	else
	{
#ifdef DEBUG_LRUCACHE
		//cout<<"memory-disk swap hadppened in VSTree - LRUCache"<<endl;
#endif
		// write out and free the memory of the least recently used one.
		int pos = this->next[LRUCache::START_INDEX];
		//cout<<pos<<" "<<_key<<" "<<_value->getFileLine()<<endl;

		int ret = 0;
#ifdef THREAD_ON
		ret = pthread_mutex_trylock(&(this->values[pos]->node_lock));
#endif
		//TODO:scan and select a unlocked one to swap, if no, then wait by cond
		if(ret != 0)  //not success
		{
			cout<<"error: fail to get the vnode lock in LRUCache::set()"<<endl;
		}
		//NOTICE:we can unlock here because user has released this lock, if he want to read 
		//this node again, he must wait for this buffer operation to end up
#ifdef THREAD_ON
		pthread_mutex_unlock(&(this->values[pos]->node_lock));
#endif

		this->writeOut(pos, this->keys[pos]);
		this->freeElem(pos);

		// set the new one to the memory pool.
		this->setElem(pos, _key, _value);
		//this->refresh(pos);
	}

#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif
	return false;
}

//Assume that the node of this key exist in memory now
bool
LRUCache::del(int _key)
{
#ifdef THREAD_ON
	pthread_rwlock_wrlock(&(this->cache_lock));
#endif

#ifdef DEBUG_LRUCACHE
	cout<<"to del in LRUCache "<<_key<<endl;
#endif
	map<int, int>::iterator iter = this->key2pos.find(_key);
	if (iter != this->key2pos.end())
	{
		int pos1 = iter->second;
		int pos2 = LRUCache::DEFAULT_NUM + this->size - 1;
#ifdef DEBUG_LRUCACHE
		cout<<"pos 1: "<<pos1<<"  pos2: "<<pos2<<endl;
#endif
		if(this->values[pos1]->getFileLine() != _key)
		{
#ifdef DEBUG_LRUCACHE
			cout<<"error in del() - file line not mapping"<<endl;
#endif
		}

		this->fillElem(pos1, pos2);
		//this->refresh(pos1);

		//NOTICE:we do not need to update the file now
		//We only record the freed file_line, and not used now
		//When this file_line is allocated again, then the new node can
		//be written into the unused file part
		//(VNode size is fixed)
#ifdef THREAD_ON
		pthread_rwlock_unlock(&(this->cache_lock));
#endif

		return true;
	}

#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif

	return false;
}

//get the value(node's pointer) by key(node's file line). 
VNode* LRUCache::get(int _key)
{
#ifdef THREAD_ON
	pthread_rwlock_rdlock(&(this->cache_lock));
#endif

	VNode* ret = NULL;
	//NOTICE:use map[] will cause the rbtree to enlarge, so we should use find
	map<int, int>::iterator iter = this->key2pos.find(_key);

	if (iter != this->key2pos.end())
	{
		int pos = iter->second;
		ret = this->values[pos];
		this->refresh(pos);
	}
	// the value is not in memory now, should load it from hard disk.
	else if (this->size < this->capacity)
	{
#ifdef THREAD_ON
		pthread_rwlock_unlock(&(this->cache_lock));
		pthread_rwlock_wrlock(&(this->cache_lock));
#endif

		//NOTICE+DEBUG:now all are loaded and there should not be any not read, goes here means error!
		//And this will cause error in multiple threads program(even if only read)
#ifdef DEBUG_LRUCACHE
		cout<<"new read hadppened in VSTree - LRUCache"<<endl;
#endif
		int pos = LRUCache::DEFAULT_NUM + this->size;
		if (this->readIn(pos, _key))
		{
			ret = this->values[pos];
			this->refresh(pos);
		}
		else
		{
			cout<<"LRUCache::get() - readIn error in the second case"<<endl;
		}
	}
	// if the memory pool is full now, should swap out the least recently used one, and swap in the required value.
	else
	{
#ifdef THREAD_ON
		pthread_rwlock_unlock(&(this->cache_lock));
		pthread_rwlock_wrlock(&(this->cache_lock));
#endif

#ifdef DEBUG_LRUCACHE
		//cout<<"memory-disk swap hadppened in VSTree - LRUCache::get()"<<endl;
#endif
		int pos = this->next[LRUCache::START_INDEX];

		int retval = 0;
#ifdef THREAD_ON
		retval = pthread_mutex_trylock(&(this->values[pos]->node_lock));
#endif
		//TODO:scan and select a unlocked one to swap, if no, then wait by cond
		if(retval != 0)  //not success
		{
			cout<<"error: fail to get the vnode lock in LRUCache::set()"<<endl;
		}
#ifdef THREAD_ON
		pthread_mutex_unlock(&(this->values[pos]->node_lock));
#endif

		this->writeOut(pos, this->keys[pos]);
		this->freeElem(pos);

		//NOTICE: readIn will call setElem to add the new node to tail
		//swap the head and push new to tail, so this is a LRU strategy
		if (this->readIn(pos, _key))
		{
			ret = this->values[pos];
			this->refresh(pos);
		}
		else
		{
			cout<<"LRUCache::get() - readIn error in the third case"<<endl;
		}
	}

#ifdef THREAD_ON
	pthread_mutex_lock(&(ret->node_lock));
	pthread_rwlock_unlock(&(this->cache_lock));
#endif

	return ret;
}

//update the _key's mapping _value. if the key do not exist, this operation will fail and return false. 
bool LRUCache::update(int _key, VNode* _value)
{
#ifdef THREAD_ON
	pthread_rwlock_wrlock(&(this->cache_lock));
#endif

	// should swap it into cache first.
	VNode* valuePtr = this->get(_key);

	if (valuePtr != NULL)
	{
		int pos = this->key2pos[_key];
		//BETTER:remove the below cerr
		if (this->keys[pos] != _key)
		{
			cerr << "error, the pos is wrong. @LRUCache::update" << endl;

#ifdef THREAD_ON
			pthread_rwlock_unlock(&(this->cache_lock));
#endif

			return false;
		}

		this->values[pos] = _value;

#ifdef THREAD_ON
		pthread_rwlock_unlock(&(this->cache_lock));
#endif

		return true;
	}

	cerr << "error:the key not exist!"<<endl;
#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif

	return false;
}

int LRUCache::getCapacity()
{
	return this->capacity;
}

int LRUCache::getRestAmount()
{
#ifdef THREAD_ON
	pthread_rwlock_rdlock(&(this->cache_lock));
#endif
	int t = this->size;
#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif

	return this->capacity - t;
	//return this->capacity - this->size;
}

void LRUCache::showAmount()
{
#ifdef THREAD_ON
	pthread_rwlock_rdlock(&(this->cache_lock));
#endif

	printf(
		"TotalAmount=%d\tUsedAmount=%d\tUsedPercent=%.2f%%\n",
		this->capacity, this->size,
		(double)this->size / this->capacity * 100.0);

#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif
}

bool LRUCache::isFull()
{
#ifdef THREAD_ON
	pthread_rwlock_rdlock(&(this->cache_lock));
#endif
	bool ret = this->size == this->capacity;
#ifdef THREAD_ON
	pthread_rwlock_unlock(&(this->cache_lock));
#endif

	return ret;
	//return this->size == this->capacity;
}

//LRU: put the new visited one to the tail 
void LRUCache::refresh(int _pos)
{
	int prevPos, nextPos;

	nextPos = this->next[_pos];
	if(nextPos == LRUCache::END_INDEX)
	{
		//already the last element
		return;
	}

	prevPos = this->prev[_pos];
	this->next[prevPos] = nextPos;
	this->prev[nextPos] = prevPos;

	prevPos = this->prev[LRUCache::END_INDEX];
	nextPos = LRUCache::END_INDEX;

	this->next[prevPos] = _pos;
	this->prev[nextPos] = _pos;

	this->next[_pos] = LRUCache::END_INDEX;
	this->prev[_pos] = prevPos;
}

//free the memory of the _pos element in cache. 
void LRUCache::freeElem(int _pos)
{
	if(_pos < LRUCache::DEFAULT_NUM || _pos >= LRUCache::DEFAULT_NUM + this->size)
	{
		cerr << "error in LRUCache::freeElem() -- invalid pos" << endl;
		return;
	}

	if(this->values[_pos] != NULL)
	{
		delete this->values[_pos];
		this->values[_pos] = NULL;
	}

	this->key2pos.erase(this->keys[_pos]);
	this->keys[_pos] = LRUCache::NULL_INDEX;

	// update the double linked list.
	int prevPos = this->prev[_pos];
	int nextPos = this->next[_pos];
	this->next[prevPos] = nextPos;
	this->prev[nextPos] = prevPos;
	this->next[_pos] = LRUCache::NULL_INDEX;
	this->prev[_pos] = LRUCache::NULL_INDEX;

	this->size--;
}

//NOTICE: setElem will append the ele to the end, so LRU is ok
//set the memory of the _pos element in cache 
void LRUCache::setElem(int _pos, int _key, VNode* _value)
{
	this->key2pos[_key] = _pos;
	this->keys[_pos] = _key;
	this->values[_pos] = _value;

	// put the new element to the tail of the linked list.
	int prevPos = this->prev[LRUCache::END_INDEX];
	int nextPos = LRUCache::END_INDEX;
	this->next[prevPos] = _pos;
	this->prev[nextPos] = _pos;
	this->next[_pos] = LRUCache::END_INDEX;
	this->prev[_pos] = prevPos;
	//NOTICE: this cannot be placed in loadCache() because this may be called by other functions
	this->size++;
}

//NOTICE: fillElem will change the pos1's next to the end, so LRU is ok(pos2 is always the current maximium position)
//move pos2 ele to pos1, and pos1 ele should be freed
void LRUCache::fillElem(int _pos1, int _pos2)
{
	cout<<"fill elem in LRUCache() happen"<<endl;

	//NOTICE:update to disk, set the node as invalid
	this->freeDisk(_pos1);
	//NOTICE:size is reduced in freeElem
	this->freeElem(_pos1);
	if(_pos1 >= _pos2)  //0 ele or 1 ele(just remove the only one)
	{
#ifdef DEBUG_LRUCACHE
		cout<<"LRUCache::fillElem() - no need to fill"<<endl;
#endif
		return;
	}

	int key = this->keys[_pos2];
#ifdef DEBUG_LRUCACHE
	cout<<"another key in fillElem() - "<<key<<endl;
#endif

	if(this->values[_pos2] == NULL)
	{
		cout<<"error in fillElem() - value for pos2 is NULL"<<endl;
	}
	this->key2pos[key] = _pos1;
	this->keys[_pos1] = key;
	this->values[_pos1] = this->values[_pos2];

	this->keys[_pos2] = LRUCache::NULL_INDEX;
	this->values[_pos2] = NULL;
	int prevPos = this->prev[_pos2];
	int nextPos = this->next[_pos2];

	//a real LRU strategy should be used, i.e. push new in tail, remove the oldest in head
	//TODO:change to list and LRU, search only keep current node is ok, but update not
	//lock: tree and buffer
	//
	//QUERY:if pos1 and pos2 are neighbors in prev-next relations
	//can this conflict with freeElem?
	this->next[prevPos] = _pos1;
	this->prev[nextPos] = _pos1;
	this->next[_pos1] = nextPos;
	this->prev[_pos1] = prevPos;
}

bool
LRUCache::freeDisk(int _pos)
{
	VNode* nodePtr = this->values[_pos];
	FILE* filePtr = fopen(this->dataFilePath.c_str(), "r+b");

	if (nodePtr == NULL)
	{
		cerr << "error, VNode do not exist. @LRUCache::freeDisk" << endl;
		return false;
	}
	if (filePtr == NULL)
	{
		cerr << "error, can't open file. @LRUCache::freeDisk" << endl;
		return false;
	}

	//size_t vNodeSize = sizeof(VNode);
	size_t vNodeSize = VNode::VNODE_SIZE;
	int line = nodePtr->getFileLine();
	int flag = 0;
	long long seekPos = (long long)line * vNodeSize;

	flag = fseek(filePtr, seekPos, SEEK_SET);

	if (flag != 0)
	{
		cerr << "error, can't seek to the fileLine. @LRUCache::writeOut" << endl;
		return false;
	}

	nodePtr->setFileLine(-1);
	//fwrite((char *)nodePtr, vNodeSize, 1, filePtr);
	nodePtr->writeNode(filePtr);

	fclose(filePtr);

	return true;
}

//just write the values[_pos] to the hard disk, the VNode in memory will not be free. 
bool 
LRUCache::writeOut(int _pos, int _fileLine)
{
	VNode* nodePtr = this->values[_pos];
	FILE* filePtr = fopen(this->dataFilePath.c_str(), "r+b");

	if (nodePtr == NULL)
	{
		cerr << "error, VNode do not exist. @LRUCache::writeOut" << endl;
		return false;
	}
	if (filePtr == NULL)
	{
		cerr << "error, can't open file. @LRUCache::writeOut" << endl;
		return false;
	}

	if (nodePtr->getFileLine() != _fileLine)
	{
		cerr << "error, fileLine " << _fileLine <<" "<< nodePtr->getFileLine() << " wrong. @LRUCache::writeOut" << endl;
	}

	if(!nodePtr->isDirty())
	{
		//cout<<"the node not dirty!"<<endl;
		fclose(filePtr);
		return true;
	}
	else //is modified
	{
		nodePtr->setDirty(false);
	}

	int line = _fileLine == -1 ? nodePtr->getFileLine() : _fileLine;
	size_t vNodeSize = VNode::VNODE_SIZE;
	//size_t vNodeSize = sizeof(VNode);
	int flag = 0;
	long long seekPos = (long long)line * vNodeSize;

	flag = fseek(filePtr, seekPos, SEEK_SET);

	if (flag != 0)
	{
		cerr << "error, can't seek to the fileLine. @LRUCache::writeOut" << endl;
		return false;
	}

	//fwrite((char *)nodePtr, vNodeSize, 1, filePtr);
	nodePtr->writeNode(filePtr);
	fclose(filePtr);

	return true;
}

//read the value from hard disk, and put it to the values[_pos].
//before use it, you must make sure that the _pos element in cache is free(unoccupied).
bool LRUCache::readIn(int _pos, int _fileLine)
{
#ifdef DEBUG_LRUCACHE
	//cout<<"pos: "<<_pos<<" "<<"fileline: "<<_fileLine<<endl;
#endif
	VNode* nodePtr = new VNode(true);
	//VNode* nodePtr = NULL;
	FILE* filePtr = fopen(this->dataFilePath.c_str(), "rb");

	//if (nodePtr == NULL)
	//{
		//cerr << "error, can not new a VNode. @LRUCache::readIn" << endl;
		//return false;
	//}

	if (filePtr == NULL)
	{
		cerr << "error, can't open " <<
			"[" << this->dataFilePath << "]" <<
			". @LRUCache::readIn" << endl;
		return false;
	}

	int line = _fileLine;
	size_t vNodeSize = VNode::VNODE_SIZE;
	//size_t vNodeSize = sizeof(VNode);
	int flag = 0;
	long long seekPos = (long long)line * vNodeSize;

	flag = fseek(filePtr, seekPos, SEEK_SET);

	if (flag != 0)
	{
		cerr << "error,can't seek to the fileLine. @LRUCache::readIn" << endl;
		return false;
	}

	//bool is_node_read = (fread((char *)nodePtr, vNodeSize, 1, filePtr) == 1);
	//fread((char *)nodePtr, vNodeSize, 1, filePtr);
	nodePtr->readNode(filePtr);
	fclose(filePtr);

	if (nodePtr == NULL || nodePtr->getFileLine() != _fileLine)
	{
		cout<<"node file line: "<<nodePtr->getFileLine()<<endl;
		cerr << "error,node fileLine error. @LRUCache::readIn" << endl;
	}

	this->setElem(_pos, _fileLine, nodePtr);

	return true;
}

//NOTICE:this can only be done by one thread
//write out all the elements to hard disk. 
bool LRUCache::flush()
{
#ifdef DEBUG_VSTREE
	cout<<"to flush in LRUCache"<<endl;
#endif
	FILE* filePtr = fopen(this->dataFilePath.c_str(), "r+b");

	if (filePtr == NULL)
	{
		cerr << "error, can't open file. @LRUCache::flush" << endl;
		return false;
	}

	int startIndex = LRUCache::DEFAULT_NUM;
	int endIndex = startIndex + this->size;
	size_t vNodeSize = VNode::VNODE_SIZE;
	//size_t vNodeSize = sizeof(VNode);

	//NOTICE:values are continuous
	for (int i = startIndex; i < endIndex; ++i)
	{
		VNode* nodePtr = this->values[i];
		int line = this->keys[i];
		//cout<<"file line to write "<<line<<endl;

#ifdef DEBUG
		if (nodePtr->getFileLine() != line)
		{
			cout << "line error at !!!" << line << " " << nodePtr->getFileLine() << endl;
		}
#endif

		if (nodePtr == NULL)
		{
			cerr << "error, VNode do not exist. @LRUCache::flush" << endl;
			return false;
		}

		if(!nodePtr->isDirty())
		{
			continue;
		}

		int flag = 0;
		long long seekPos = (long long)line * vNodeSize;
		flag = fseek(filePtr, seekPos, SEEK_SET);

		if (flag != 0)
		{
			cerr << "error, can't seek to the fileLine. @LRUCache::flush" << endl;
			return false;
		}

		//fwrite((char *)nodePtr, vNodeSize, 1, filePtr);
		nodePtr->writeNode(filePtr);
	}
	fclose(filePtr);

	return true;
}