//reference a page which is already in the page table
public void reference(int frameId, int step)
{
foreach (PageTableEntry pte in entryList)
{
if (pte.getFrame() == frameId)
{
pte.setModified(step);
//see if the page table entry is not in physical mem
if (!pte.isResident())
{
pm.addPage(pte, step);
}
break;
}
}
}
public void addPage(int frameId, int step)
{
bool added = false;
for (int x = 0; x < 16; x++)
{
//an empty valid frame was found in page table
if (entryList[x].isEmpty())
{
entryList[x].setFrame(frameId);
added = true;
pm.addPage(entryList[x], owningProcess.getPid());
break;
}
}
if (added)
{
return;
}
//a valid page wasnt found, make room for the frame in valid page
int leasedUsed = 0;
int leasedUsedIndex = 0;
int index = 0;
foreach (PageTableEntry pte in entryList)
{
//find the page which was lease recently used
int timeDelta = step - pte.getLastModified();
if (timeDelta > leasedUsed)
{
leasedUsed = timeDelta;
leasedUsedIndex = index;
}
index++;
}
//save a copy of the frame being removed in next open space
//TODO: if the frame being removed was in memory, do proper computations
for (int x = 16; x < 64; x++)
{
if (entryList[x].isEmpty())
{
//copy page info to new frame
PageTableEntry pte = entryList[x];
pte.setFrame(entryList[index].getFrame());
pte.setModified(step);
pte.setResident(false);
pte.setValid(false);
break;
}
}
//overwrite the old valid page
PageTableEntry npte = entryList[index];
npte.setFrame(frameId);
npte.setModified(step);
pm.addPage(npte, owningProcess.getPid());
}