feat(assign5): ✨ implement LRU replacement algorithm

Author: lutrine

assign5/lru_replacement.cpp

@@ -1,41 +1,59 @@
 /**
-* Assignment 5: Page replacement algorithms
+ * Assignment 5: Page replacement algorithms
  * @file lru_replacement.cpp
- * @author ??? (TODO: your name)
+ * @author Caden Jamason and Adrian Reyes
  * @brief A class implementing the LRU page replacement algorithms
  * @version 0.1
  */
-//You must complete the all parts marked as "TODO". Delete "TODO" after you are done.
-// Remember to add sufficient and clear comments to your code
 
 #include "lru_replacement.h"
 
-// TODO: Add your implementation here
 LRUReplacement::LRUReplacement(int num_pages, int num_frames)
-: Replacement(num_pages, num_frames)
-{
-    // TODO: Complete this constructor
-}
+    : Replacement(num_pages, num_frames) {}
 
-// TODO: Add your implementations for desctructor, touch_page, load_page, replace_page here
-LRUReplacement::~LRUReplacement()
-{
-    // TODO: Add necessary code here
-}
+LRUReplacement::~LRUReplacement() {}
 
-// Accesss a page alreay in physical memory
-void LRUReplacement::touch_page(int page_num)
-{
-    // TODO: Update your data structure LRU replacement
+void LRUReplacement::touch_page(int page_num) {
+  // Move accessed page to front of list
+  lru_list.erase(page_map[page_num]);
+  lru_list.push_front(page_num);
+  page_map[page_num] = lru_list.begin();
 }
 
-// Access an invalid page, but free frames are available
 void LRUReplacement::load_page(int page_num) {
-    // TODO: Update your data structure LRU replacement and pagetable
+  // Calculate frame number for new page
+  int frame_num = total_frames - free_frames;
+
+  // Update page table with frame number and mark page as valid
+  page_table[page_num].frame_num = frame_num;
+  page_table[page_num].valid = true;
+
+  // Move new page to front of list
+  lru_list.push_front(page_num);
+  page_map[page_num] = lru_list.begin();
 }
 
-// Access an invalid page and no free frames are available
 int LRUReplacement::replace_page(int page_num) {
-    // TODO: Update your data structure LRU replacement and pagetable
-    return 0;
-}
+  // Least recently used page is at the back of the list
+  int victim_page = lru_list.back();
+  lru_list.pop_back();
+
+  // Update page table for victim page
+  page_table[victim_page].valid = false;
+
+  // Use the frame of the victim page for the new page
+  page_table[page_num].frame_num = page_table[victim_page].frame_num;
+
+  // Update page table for new page
+  page_table[page_num].valid = true;
+
+  // Move new page to front of list
+  lru_list.push_front(page_num);
+  page_map[page_num] = lru_list.begin();
+
+  // Remove victim page from map
+  page_map.erase(victim_page);
+
+  // Return victim page number
+  return victim_page;
+}

assign5/lru_replacement.h

@@ -1,58 +1,61 @@
 /**
-* Assignment 5: Page replacement algorithms
+ * Assignment 5: Page replacement algorithms
  * @file lru_replacement.h
- * @author ??? (TODO: your name)
+ * @author Caden Jamason and Adrian Reyes
  * @brief A class implementing the LRU page replacement algorithms
  * @version 0.1
  */
-//You must complete the all parts marked as "TODO". Delete "TODO" after you are done.
-// Remember to add sufficient and clear comments to your code
 
 #pragma once
 
-// Remember to add comments to your code
-
 #include "replacement.h"
+#include <list>
+#include <unordered_map>
 
 /**
- * @brief A class to simulate the least recently used (LRU) page replacement algorithm.
+ * @brief A class to simulate the least recently used (LRU) page replacement
+ * algorithm.
  */
-class LRUReplacement : public Replacement
-{
-	// TODO: Add your implementation to this class
+class LRUReplacement : public Replacement {
+private:
+  // Maintains order of page accesses
+  std::list<int> lru_list;
+
+  // Stores page number and its corresponding iterator in list
+  std::unordered_map<int, std::list<int>::iterator> page_map;
+
 public:
-	/**
-	 * @brief Constructor
-	 * @param num_pages 
-	 * @param num_frames 
-	 */
-	LRUReplacement(int num_pages, int num_frames);
-	
-    /**
-    * @brief Destructor
-    */
-    virtual ~LRUReplacement();
-
-    /**
-     * @brief Accesss a page alreay in physical memory
-     * It may be overridden in a subclass 
-     * @param page_num The logical page number.
-     */
-    virtual void touch_page(int page_num);
-
-    /**
-     * @brief Access an invalid page, but free frames are available.
-     * Assign the page to an available  frame, not replacement needed
-     * @param page_num The logical page number.
-     */
-    virtual void load_page(int page_num);
-
-    /**
-     * @brief Access an invalid page, and there is no free frame.
-     * Replace the page with the page that has been in memory the longest.
-     * @param page_num The logical page number.
-     * @return Selected victim page #
-     */
-    virtual int replace_page(int page_num);
-
-};
+  /**
+   * @brief Constructor
+   * @param num_pages
+   * @param num_frames
+   */
+  LRUReplacement(int num_pages, int num_frames);
+
+  /**
+   * @brief Destructor
+   */
+  virtual ~LRUReplacement();
+
+  /**
+   * @brief Accesss a page already in physical memory
+   * It may be overridden in a subclass
+   * @param page_num The logical page number.
+   */
+  virtual void touch_page(int page_num);
+
+  /**
+   * @brief Access an invalid page, but free frames are available.
+   * Assign the page to an available frame, not replacement needed
+   * @param page_num The logical page number.
+   */
+  virtual void load_page(int page_num);
+
+  /**
+   * @brief Access an invalid page, and there is no free frame.
+   * Replace the page with the page that has been in memory the longest.
+   * @param page_num The logical page number.
+   * @return Selected victim page #
+   */
+  virtual int replace_page(int page_num);
+};