/*
* Allocates a free frame using the clock algorithm;
* if necessary, writing a dirty page back to disk.
*
* Throws BufferExceededException if all buffer frames are pinned.
* params: FrameId & frame
*/
void BufMgr::allocBuf(FrameId & frame)
{
uint32_t pinnedPageCnt = 0;
// implementation of the clock algorithm
// remember to change the while(true)
while(true) {
advanceClock();
BufDesc* tmpbuf = &(bufDescTable[clockHand]);
// if invalid then allocate this page
if (tmpbuf->valid == false) {
frame = clockHand;
return;
}
// if refbit is set then clear and advance clock
else if (tmpbuf->refbit == true) {
tmpbuf->refbit = false;
continue;
}
// ignore if page pinned
else if (tmpbuf->pinCnt > 0) {
pinnedPageCnt = pinnedPageCnt + 1;
if(pinnedPageCnt >= numBufs) {
throw BufferExceededException();
}
continue;
}
// frame can be used
// if the page is dirty flush to disk
if (tmpbuf->dirty == true) {
tmpbuf->file->writePage(bufPool[clockHand]);
tmpbuf->dirty = false;
}
// now we can select this frame
frame = clockHand;
//remove from hashtable
hashTable->remove(tmpbuf->file, tmpbuf->pageNo);
return;
}
}
/**
* Allocate a free frame.
*
* @param frame Frame reference, frame ID of allocated frame returned via this variable
* @throws BufferExceededException If no such buffer is found which can be allocated
*/
void BufMgr::allocBuf(FrameId & frame)
{
bool found = false;
FrameId starting = clockHand;
//Loop through the buffer pool until you find a valid frame to replace
while(!found){
advanceClock();
if(bufDescTable[clockHand].valid){
if(!bufDescTable[clockHand].refbit){
if(bufDescTable[clockHand].pinCnt == 0){
//we have found the correct frame
found = true;
hashTable->remove(bufDescTable[clockHand].file, bufDescTable[clockHand].pageNo); //remove from hash table
if(bufDescTable[clockHand].dirty){
//write page to disk.
bufDescTable[clockHand].file->writePage(bufPool[clockHand]);
}
else{
bufDescTable[clockHand].Clear();
}
frame = bufDescTable[clockHand].frameNo;
}
else{
if(starting == clockHand && !found){
//we looped all the way around the buffer pool, throw an exception
throw BufferExceededException();
}
}
}
else{
//clear refbit
bufDescTable[clockHand].refbit = false;
}
}
else{
found = true;
frame = bufDescTable[clockHand].frameNo;
}
}
bufDescTable[clockHand].Clear();
}
void BufMgr::allocBuf(FrameId & frame)
{
std::uint32_t scanner = 0;
bool cont = 0;
while(scanner < 2*numBufs){
advanceClock();
scanner++;
if(bufDescTable[clockHand].valid == false){
break;
}
if(!(bufDescTable[clockHand].refbit)){
if(bufDescTable[clockHand].pinCnt == 0){
hashTable->remove(bufDescTable[clockHand].file, bufDescTable[clockHand].pageNo);
cont = true;
break;
}
}
else{
bufStats.accesses++;
bufDescTable[clockHand].refbit = false;
}
}
if((!cont) && (scanner >= 2*numBufs-1)){
throw BufferExceededException();
}
if(bufDescTable[clockHand].dirty && bufDescTable[clockHand].valid){
bufStats.diskwrites++;
bufDescTable[clockHand].file->writePage(bufPool[clockHand]);
}
bufDescTable[clockHand].Clear();
//bufDescTable[clockHand].Set(bufDescTable[clockHand].file, bufDescTable[clockHand].pageNo);
frame = clockHand;
}
/*
*
* Allocate a free frame.
*
* @param frame Frame reference, frame ID of allocated frame returned via this variable
* @throws BufferExceededException If no such buffer is found which can be allocated
*/
void BufMgr::allocBuf(FrameId & frame)
{
std::uint32_t clock_count = 0;
//clock algorithm
while(1){
advanceClock();
if(bufDescTable[clockHand].valid == true){
if(bufDescTable[clockHand].refbit == true){
bufDescTable[clockHand].refbit = false;
//skip all the steps below and loop again
continue;
}
if(bufDescTable[clockHand].pinCnt > 0){
clock_count++;
//if every pages is being pinned in buffer pool, throw exception
if(clock_count > numBufs){
throw BufferExceededException();
}
continue;
}
if(bufDescTable[clockHand].dirty == true){
flushFile(bufDescTable[clockHand].file);
bufDescTable[clockHand].dirty = false;
}
else{
hashTable->remove(bufDescTable[clockHand].file, bufDescTable[clockHand].pageNo);
}
break;
}
else{
break;
}
}
frame = bufDescTable[clockHand].frameNo;
}
