/****************************************************************
*
* This method handles the next command in the pcb. It loads the
* process into a new page table, then it loads it into memory.
* If it is a halt command, it removes the process from memory
* and the page tablefrom the list of page tables.
*
* Returns a -1 if it is at the end of the pcb otherwise it returns
* the number of commands left.
*
***************************************************************/
public int Next()
{
if (pcb.Count < 1)
{
return(-1);
}
// remove the next command and place into c
Command c = pcb[0];
pcb.RemoveAt(0);
//previousPcb.Insert(0, pcb[0]);
//previousFreeFrames.Insert(0, freeFrames);
// check if it is a halt command or not
if (c.TextSize >= 0)
{
//previousPageTables.Insert(0, pageTable);
//previousMemory.Insert(0, memory);
// create a new page table for the new process
PageTable pt = new PageTable(c);
pt.SetPages();
pageTable.Add(pt);
// load the page into memory
LoadIntoMemory(pageTable.Last());
}
else // it was a halt command
{
// loops through all memory frames and if it contains the process
// that is being halted, remove it from memory
for (int x = 0; x <= 7; x++)
{
if (memory[x] != null && memory[x].ProcessID == c.ProcessID)
{
memory[x] = null;
// add that frame to the free frames list
freeFrames.Add(x);
}
}
// loops through page tables and remove the page table that is for the
// halting process
for (int i = pageTable.Count - 1; i >= 0; i--)
{
if (pageTable[i].ProcessID == c.ProcessID)
{
pageTable.Remove(pageTable[i]);
}
}
}
return(pcb.Count);
}
//public int Previous()
//{
// pcb.Insert(0, previousPcb[0]);
// previousPcb.RemoveAt(0);
// memory = previousMemory[0];
// previousMemory.RemoveAt(0);
// pageTable = previousPageTables[0];
// previousPageTables.RemoveAt(0);
// freeFrames = previousFreeFrames[0];
// previousFreeFrames.RemoveAt(0);
// return previousPcb.Count;
//}
/*****************************************************************
*
* This method takes a page table and loads it into memory.
*
****************************************************************/
private void LoadIntoMemory(PageTable pt)
{
MFrame mf;
// loops through page table and adds each page to the next available frame
// in memory
foreach (ProcessPage p in pt.Pages)
{
mf = new MFrame(p);
// grab the next free frame
int freeFrame = freeFrames[0];
freeFrames.RemoveAt(0);
// set the page tabels frame value to the frame its being placed in
p.FrameNumber = freeFrame;
// set the frame value of the frame
mf.FrameNumber = freeFrame;
// place frame into memory in the free frame
memory[freeFrame] = mf;
}
}
