WorkingSet.cpp

#include "WSPage.cpp"

/**
@author: Robert Howerton
@description: This program is designed to demonstrate the working set page replacement algorithm.
@function: The working set algorithm employs a timer, a "working set" (hence the name), and a moving time window of fixed size T
the time window moves across the working set. If a particular page is not referenced for 4 iterations, that page's location
is automatically freed for use by another page.


--Moving Window         :int value keeping track of the page window size
--wSet                  :char array keeping a working set of all characters in the current working set
*/


class WorkingSet {

private:

    WSPage * WSTable;
    int WSTableSize;
    int t;

public:

#define MOVINGWINDOW = 4;


    WorkingSet(int size) {
        WSTableSize = size;
        WSTable = new WSPage[size];
    }


/**method to check for the requested page
//@param char: page to be checked for
//@return: true if found, false if not found
/
*/

    bool checkForPage(char page) {
        executor(); //initializes the executor method
        int inc; //incrementer

        for (int i = 0; i < WSTableSize; i++) {
            if (WSTable[i].getName() == page) {
      //          cout << "Found page " << page << " at pos " << i << endl;
                WSTable[i].use();
                return true;
                break;
            }
        }

        for (inc = 0; inc < WSTableSize; inc++) {
            if (WSTable[inc].isSet() != true) { //checks whether the page was set or not
    //            cout << "Empty page at " << inc << " adding page " << page << endl;
                WSTable[inc].setName(page); //sets name of the page at the table's current index to the name of the page replacing it
                WSTable[inc].use(); //sets new age for page at that location
                return false;
                break;
            }
        }

  //      cout << "Page fault looking for: " << page << endl;
        //declares new index for oldest page, sets value using getOldest method
        int tempIndex = getPageWithGreatestIterationsSinceLastReference();
        WSTable[tempIndex].setName(page); //replaces oldest page with the needed page
//        cout << "Added " << page << " to " << tempIndex << " : " << WSTable[tempIndex].getName() << endl;
        WSTable[tempIndex].use(); //sets new age for page at that location
        return false;

        return 0;
    }


/**
Method to cycle through the working set and delete old pages (outside time window 4)
this method will also maintain the working set. Ideally, this method will execute during the entirety of the program's runtime

@param void
@return void
*/

    void executor(void) {
/** int t is the time window incrementer
* t will start at 0 and increment to 3 over time. once 3 is reached (4 total iterations), the entire WS Table is cycled through and all pages which
* are not set are deleted.*/

        if (t == 3) {
            t = 0;
            /*If the target page is not marked AND not in the working set, delete it*/
            for (int k = 0; k < WSTableSize; k++) {
                if (!WSTable[k].isReffed() && findInWorkingSet(WSTable[k]) == false) WSTable[k].setName('\0');
            }
        }
        else
            t++;

    }

/**
*method used to find target page in the working set
@param page to be looked for
@return boolean true if found, false if not found
*/

    bool findInWorkingSet(WSPage page) {

        for (int i = 0; i < WSTableSize; i++) {
            if (WSTable[i].isInWS()) return true;
        }

        return false;
    }

    /**
    *Finds the page with the greatest number of time iterations since the last reference. This is a condition on which
    * to handle page faults. If a page fault occurs, the "preferred" page to be replaced is the one with the greatest
    * number iterations since the last page reference
    * @param void
    * @return int: returns the index value of the page with the greatest number of iterations since last use*/

    int getPageWithGreatestIterationsSinceLastReference(void){
        int tempGreatestIndex = 0;
        int tempGreatestIts = WSTable[0].getIts();
        for (int i = 0; i < WSTableSize; i ++){
            if (tempGreatestIts < WSTable[i].getIts()){
                tempGreatestIndex = i;
                tempGreatestIts = WSTable[i].getIts();
            }
        }
        return tempGreatestIndex;

    }

};