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others/lru_cache.cpp
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@ -1,44 +1,55 @@
/**
* @file
* @brief An implementation of
* [LRU Cache](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)).
* Lru is a part of cache algorithms (also frequently called cache replacement algorithms or cache replacement policies).
* [LRU
* Cache](https://en.wikipedia.org/wiki/Cache_replacement_policies#Least_recently_used_(LRU)).
* Lru is a part of cache algorithms (also frequently called cache replacement
* algorithms or cache replacement policies).
*
* ### Logic:
* * Discards the least recently used items first.
* * This algorithm requires keeping track of what was used when, which is expensive if one wants to make sure the
* algorithm always discards the least recently used item.
* * General implementations of this technique require keeping "age bits" for cache-lines and track the
* "Least Recently Used" cache-line based on age-bits.
* * In such an implementation, every time a cache-line is used, the age of all other cache-lines changes
* * This algorithm requires keeping track of what was used when, which is
* expensive if one wants to make sure the algorithm always discards the least
* recently used item.
* * General implementations of this technique require keeping "age bits"
* for cache-lines and track the "Least Recently Used" cache-line based on
* age-bits.
* * In such an implementation, every time a cache-line is used, the age of
* all other cache-lines changes
*
* ### Algorithm explanation:
* For a cache of page frame x:
* * Check if the page is present in cache.
* * If not present, then check is the cache is full or not:
* * If the cache is full, REMOVE the last element from the cache.
* * If the element is present in cache, then shift that element to first position in cache from its original position.
* * This way you can keep the least recently used elements in the last and most recently used in front of the cache.
* * If the element is present in cache, then shift that element to
* first position in cache from its original position.
* * This way you can keep the least recently used elements in the
* last and most recently used in front of the cache.
*
* Every time a requested page is not found in cache, that is a miss or page fault, and if the page is present in
* cache, then its a hit.
* Every time a requested page is not found in cache, that is a miss or page
* fault, and if the page is present in cache, then its a hit.
*
* ## Data Structure used:
* * In the algorithm below we used two different data structure, one is linked list and other one is a hash map
* * The linked list is used to contain the pages and the hash map contains the pages and their address.
* * Every time a new page is requested, we first check in the hash map if the page is present or not.
* * If not present, and the cache is full, we simply delete the last entry in the cache.
* * If present, we shift that page from its current location to beginning of the cache and update the address in
* hash map for that page.
* * In the algorithm below we used two different data structure, one is linked
* list and other one is a hash map
* * The linked list is used to contain the pages and the hash map contains the
* pages and their address.
* * Every time a new page is requested, we first check in the hash map if the
* page is present or not.
* * If not present, and the cache is full, we simply delete the last entry in
* the cache.
* * If present, we shift that page from its current location to beginning of
* the cache and update the address in hash map for that page.
*
* @author [Nitin Sharma](https://github.com/foo290)
* */
#include <iostream> /// for assert
#include <cassert> /// for IO Operations
#include <bits/stdc++.h> /// for std::vector
#include <cassert> /// for IO Operations
#include <iostream> /// for assert
/**
* @namespace lru_cache
* @brief Implementation of LRU caching algorithm
@ -51,19 +62,20 @@ namespace lru_cache {
class LRUCache {
int pageFrame; ///< Page frame, or total size of the cache.
std::list<int> cache; ///< Cache linked list (using the STL)
std::unordered_map<int, std::list<int>::iterator> pageMap; ///< Hash map containing pages and their addresses
std::unordered_map<int, std::list<int>::iterator>
pageMap; ///< Hash map containing pages and their addresses
int hits = 0; ///< Total number of hits, or total number of times a page was found in cache.
int pageFault = 0; ///< Total number of miss/page fault, or total number of times a page was not found in cache
int hits = 0; ///< Total number of hits, or total number of times a page
///< was found in cache.
int pageFault = 0; ///< Total number of miss/page fault, or total number of
///< times a page was not found in cache
public:
/**
* @brief Constructor, Initialize thee LRU class with page frame.
* @param pf Page frame or total size of cache.
* */
explicit LRUCache(int pf) {
pageFrame = pf;
}
explicit LRUCache(int pf) { pageFrame = pf; }
/**
* @brief Refer to a page, or request a page from memory.
@ -77,7 +89,6 @@ namespace lru_cache {
// Check if the cache is full
if (cache.size() == pageFrame) {
// delete the last page from cache
int lastPage = cache.back();
cache.pop_back();
@ -90,7 +101,8 @@ namespace lru_cache {
// present in cache, erase from current position to bring in front
cache.erase(pageMap[page]);
}
// Push it in the front of the cache and update the page reference in page map.
// Push it in the front of the cache and update the page reference in
// page map.
cache.push_front(page);
pageMap[page] = cache.begin();
}
@ -109,17 +121,12 @@ namespace lru_cache {
* @brief A function to get page hits
* @returns int
* */
int getHits() const{
return hits;
}
int getHits() const { return hits; }
/**
* @brief A function to get page fault
* @returns int
* */
int getPageFault() const{
return pageFault;
}
int getPageFault() const { return pageFault; }
};
} // namespace lru_cache
@ -138,7 +145,8 @@ namespace lru_tests {
/**
* @brief A simple test case
* The assert statement will check expected hist and miss to resultant hits and miss
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_1() {
@ -156,14 +164,16 @@ namespace lru_tests {
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits && cache.getPageFault() == expected_pageFault);
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-1 complete!");
}
/**
* @brief A test case contains hits more than cache size
* The assert statement will check expected hist and miss to resultant hits and miss
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_2() {
@ -181,14 +191,16 @@ namespace lru_tests {
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits && cache.getPageFault() == expected_pageFault);
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-2 complete!");
}
/**
* @brief A simple test case
* The assert statement will check expected hist and miss to resultant hits and miss
* The assert statement will check expected hist and miss to resultant hits and
* miss
* @returns void
* */
static void test_3() {
@ -206,7 +218,8 @@ namespace lru_tests {
cache.refer(5);
log("Checking assert statement...");
assert(cache.getHits() == expected_hits && cache.getPageFault() == expected_pageFault);
assert(cache.getHits() == expected_hits &&
cache.getPageFault() == expected_pageFault);
log("Assert successful!");
log("Test-3 complete!");
}
@ -244,7 +257,7 @@ int main() {
cache.display();
std::cout<<"Hits: "<< cache.getHits() << " Miss: " << cache.getPageFault();
std::cout << "Hits: " << cache.getHits()
<< " Miss: " << cache.getPageFault();
return 0;
}