Question

ModifyreplacePage()inPageFault.javato implement around robinpage replacement algorithm (i.e., first page fault replaces page 0, next one replaces page 1, next one replaces page 2, etc.).

This is the PageFault.java

/* It is in this file, specifically the replacePage function that will

be called by MemoryManagement when there is a page fault.The

users of this program should rewrite PageFault to implement the

page replacement algorithm.

*/

// This PageFault file is an example of the FIFO Page Replacement

// Algorithm as described in the Memory Management section.

import java.util.*;

import Page;

public class PageFault {

/**

* The page replacement algorithm for the memory management sumulator.

* This method gets called whenever a page needs to be replaced.

*

* The page replacement algorithm included with the simulator is

* FIFO (first-in first-out).A while or for loop should be used

* to search through the current memory contents for a canidate

* replacement page.In the case of FIFO the while loop is used

* to find the proper page while making sure that virtPageNum is

* not exceeded.

*

 
*Page page = ( Page ) mem.elementAt( oldestPage )
 
* 

* This line brings the contents of the Page at oldestPage (a

* specified integer) from the mem vector into the page object.

* Next recall the contents of the target page, replacePageNum.

* Set the physical memory address of the page to be added equal

* to the page to be removed.

*

 
*controlPanel.removePhysicalPage( oldestPage )
 
* 

* Once a page is removed from memory it must also be reflected

* graphically.This line does so by removing the physical page

* at the oldestPage value.The page which will be added into

* memory must also be displayed through the addPhysicalPage

* function call.One must also remember to reset the values of

* the page which has just been removed from memory.

*

* @param mem is the vector which contains the contents of the pages

*in memory being simulated.mem should be searched to find the

*proper page to remove, and modified to reflect any changes.

* @param virtPageNum is the number of virtual pages in the

*simulator (set in Kernel.java).

* @param replacePageNum is the requested page which caused the

*page fault.

* @param controlPanel represents the graphical element of the

*simulator, and allows one to modify the current display.

*/

public static void replacePage ( Vector mem , int virtPageNum , int replacePageNum , ControlPanel controlPanel )

{

int count = 0;

int oldestPage = -1;

int oldestTime = 0;

int firstPage = -1;

int map_count = 0;

boolean mapped = false;

while ( ! (mapped) || count != virtPageNum ) {

Page page = ( Page ) mem.elementAt( count );

if ( page.physical != -1 ) {

if (firstPage == -1) {

firstPage = count;

}

if (page.inMemTime > oldestTime) {

oldestTime = page.inMemTime;

oldestPage = count;

mapped = true;

}

}

count++;

if ( count == virtPageNum ) {

mapped = true;

}

}

if (oldestPage == -1) {

oldestPage = firstPage;

}

Page page = ( Page ) mem.elementAt( oldestPage );

Page nextpage = ( Page ) mem.elementAt( replacePageNum );

controlPanel.removePhysicalPage( oldestPage );

nextpage.physical = page.physical;

controlPanel.addPhysicalPage( nextpage.physical , replacePageNum );

page.inMemTime = 0;

page.lastTouchTime = 0;

page.R = 0;

page.M = 0;

page.physical = -1;

}

}