/// <summary>
/// Initializez the page at the beginning of the simulation.
/// Called by the PageTable once, when the OS requires the initialization of the page table.
/// </summary>
/// <param name="index">The index of the page in the page table.</param>
internal Page(int index)
{
IsValid = false;
PageIndex = index;
IsDirty = false;
Requested = -1;
LastTimeAccessed = CurrentTimeGetter.GetCrtTime();
}
/// <summary>
/// Method that handles the load of a page from disk to RAM.
/// Sets the Requested field of the page with the process' pid and calls the OS to load it.
/// After the OS loaded it, the MMU is notified and resets the Requested field.
/// </summary>
/// <param name="command">Represents the received command (read / write).</param>
/// <param name="page">The page for which the request was made.</param>
private async static Task HandlePageRequested(Command command, Page page)
{
page.Requested = command.ProcessId;
page.LastTimeAccessed = CurrentTimeGetter.GetCrtTime();
await OS.LoadPage(page);
page.Requested = -1;
page.IsValid = true;
}
/// <summary>
/// Method that handles the actual read / write command.
/// If the command is write, it simulates the handling by asking the OS to save changes to disk (if page is dirty)
/// and resets the dirty bit.
/// </summary>
/// <param name="command">Represents the received command (read / write).</param>
/// <param name="page">The page for which the request was made.</param>
private async static Task HandleReadWriteCommand(Command command, Page page)
{
page.LastTimeAccessed = CurrentTimeGetter.GetCrtTime();
if (command.AccessType == PageAccessType.Write)
{
if (page.IsDirty)
{
await OS.SavePageChangesToDisk(page);
}
page.IsDirty = true;
}
}
/// <summary>
/// Simulates asynchronously the process of swapping a page when the RAM is fully loaded and another page needs to be loaded.
/// </summary>
/// <param name="swapPage">The page to be placed in the RAM instead of an old, unused one.</param>
private async static Task SwapPage(Page swapPage)
{
(Page pageToSwap, int pid) = GetPageToBeSwapped();
if (pageToSwap.IsDirty)
{
await SavePageChangesToDisk(pageToSwap);
pageToSwap.IsDirty = false;
}
pageToSwap.IsValid = false;
pageToSwap.LastTimeAccessed = CurrentTimeGetter.GetCrtTime();
Counter.IncrementPageSwaps();//Incremented for each swap. Ensures the correctness of the program's logic.
LoadRamFrame(swapPage, FindIndexInRam(pid, pageToSwap.PageIndex));
}
/// <summary>
/// Method that gets the page that willl be swapped, from all the processes and their page tables.
/// </summary>
/// <returns>A tuple containing the page to be swapped and the pid of the process it belongs to.</returns>
private static (Page PageToSwap, int Pid) GetPageToBeSwapped()
{
string lastAccess = CurrentTimeGetter.GetCrtTime();
Page pageToSwap = new Page(-1);
int pid = -1;
foreach (var process in Processes)
{
foreach (var page in process.PageTable.Pages)
{
if (page.IsValid)
{
if (page.LastTimeAccessed.CompareTo(lastAccess) < 0)
{
pageToSwap = page;
lastAccess = page.LastTimeAccessed;
pid = process.Pid;
}
}
}
}
return(pageToSwap, pid);
}