lru_cache.cpp File Reference

An implementation of LRU Cache. Lru is a part of cache algorithms (also frequently called cache replacement algorithms or cache replacement policies). More...

#include <cassert>
#include <cstdint>
#include <iostream>
#include <list>
#include <unordered_map>

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Classes
class	others::lru_cache::LRUCache
	LRU cache class. More...

Namespaces
namespace	others
	for vector
namespace	lru_cache
	Implementation of the LRU caching algorithm

Functions
template<typename T >
void	lru_tests::log (T msg)
	A function to print given message on console.
static void	lru_tests::test_1 ()
	A simple test case The assert statement will check expected hist and miss to resultant hits and miss.
static void	lru_tests::test_2 ()
	A test case contains hits more than cache size The assert statement will check expected hist and miss to resultant hits and miss.
static void	lru_tests::test_3 ()
	A simple test case The assert statement will check expected hist and miss to resultant hits and miss.
static void	lru_tests::run_tests ()
	A function to invoke all test cases.
int	main ()
	Main function.

Detailed Description

An implementation of LRU Cache. 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

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.

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.

Author

Nitin Sharma

Function Documentation

log()

template<typename T >

void lru_tests::log

(

T

msg

)

A function to print given message on console.

Template Parameters

T	Type of the given message.

Returns

void

                {
    // It's just to avoid writing cout and endl
    std::cout << "[TESTS] : ---> " << msg << std::endl;
}

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main()

int main

(

void

)

Main function.

Returns

0 on exit

           {
    lru_tests::run_tests();
 
    // Usage
    others::lru_cache::LRUCache cache(4);
    cache.refer(1);
    cache.refer(2);
    cache.refer(3);
    cache.refer(4);
    cache.refer(5);
    cache.refer(5);
 
    cache.display();
 
    std::cout << "Hits: " << cache.getHits()
              << " Miss: " << cache.getPageFault() << std::endl;
    return 0;
}

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run_tests()

static void lru_tests::run_tests ( )

static

A function to invoke all test cases.

Returns

void

                        {
    test_1();
    test_2();
    test_3();
    log("");
    log("TESTS COMPLETED!");
}

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test_1()

static void lru_tests::test_1 ( )

static

A simple test case The assert statement will check expected hist and miss to resultant hits and miss.

Returns

void

                     {
    uint64_t expected_hits = 2;
    uint64_t expected_pageFault = 4;
 
    log("Running Test-1...");
 
    others::lru_cache::LRUCache cache(4);
    cache.refer(1);
    cache.refer(2);
    cache.refer(5);
    cache.refer(1);
    cache.refer(4);
    cache.refer(5);
 
    log("Checking assert statement...");
    assert(cache.getHits() == expected_hits &&
           cache.getPageFault() == expected_pageFault);
    log("Assert successful!");
    log("Test-1 complete!");
}

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test_2()

static void lru_tests::test_2 ( )

static

A test case contains hits more than cache size The assert statement will check expected hist and miss to resultant hits and miss.

Returns

void

                     {
    uint64_t expected_hits = 4;
    uint64_t expected_pageFault = 2;
 
    log("Running Test-2...");
 
    others::lru_cache::LRUCache cache(4);
    cache.refer(1);
    cache.refer(1);
    cache.refer(1);
    cache.refer(1);
    cache.refer(1);
    cache.refer(5);
 
    log("Checking assert statement...");
    assert(cache.getHits() == expected_hits &&
           cache.getPageFault() == expected_pageFault);
    log("Assert successful!");
    log("Test-2 complete!");
}

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test_3()

static void lru_tests::test_3 ( )

static

A simple test case The assert statement will check expected hist and miss to resultant hits and miss.

Returns

void

                     {
    uint64_t expected_hits = 1;
    uint64_t expected_pageFault = 5;
 
    log("Running Test-3...");
 
    others::lru_cache::LRUCache cache(4);
    cache.refer(1);
    cache.refer(2);
    cache.refer(3);
    cache.refer(4);
    cache.refer(5);
    cache.refer(5);
 
    log("Checking assert statement...");
    assert(cache.getHits() == expected_hits &&
           cache.getPageFault() == expected_pageFault);
    log("Assert successful!");
    log("Test-3 complete!");
}

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