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ReplacementPolicies.h
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ReplacementPolicies.h
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#pragma once
#include <bits/stdc++.h>
#include "globalVariables.h"
using namespace std;
template <typename T>
pair<T*, int> tryFillingTable(vector<T*> &table, T* new_entry){
typename vector<T*>::iterator repl=table.begin();
int old_index = -1;
//check the table for the earliest empty space
int i = 0;
for(typename vector<T*>::iterator it=table.begin();it!=table.end();it++)
{
if((*it) == NULL)
{
repl=it;
old_index = i;
break;
}
i++;
}
if(old_index != -1){
// We have identified the empty space
*repl = new_entry;
}
return {NULL, old_index};
}
/*
policy_type::
0 : FIFO
1 : LRU
2 : Optimal
*/
template <typename T>
pair<T*, int> replacement(int policy_type, vector<T*> &table, T* new_entry, int access_index=0)
{
// First lets check if there is empty space available, hence no replacement needed;
pair<T*, int> old = tryFillingTable(table, new_entry);
if(old.second != -1){
return old;
}
T* old_entry = NULL; // will return this after modifying the table;
int old_index = -1;
//for FIFO replacement
if(policy_type==0)
{
int min_arrival_time=INT_MAX;
typename vector<T*>::iterator repl=table.begin();
//check the table for the earliest/first entry
int i = 0;
for(typename vector<T*>::iterator it=table.begin();it!=table.end();it++)
{
if((*it)->arrival_time_stamp<min_arrival_time)
{
min_arrival_time=(*it)->arrival_time_stamp;
repl=it;
old_index = i;
}
i++;
}
old_entry = *repl;
*repl=new_entry; //replace the old entry with the new entry
}
//for LRU replacement
else if(policy_type==1)
{
int min_recent_usage=INT_MAX;
typename vector<T*>::iterator repl=table.begin();
//check the table for the least recently used entry
int i = 0;
for(typename vector<T*>::iterator it=table.begin();it!=table.end();it++)
{
if((*it)->recent_usage_time_stamp<min_recent_usage)
{
min_recent_usage=(*it)->recent_usage_time_stamp;
repl=it;
old_index = i;
}
i++;
}
old_entry = *repl;
*repl=new_entry; //replace the old entry with the new entry
}
//for optimal replacement
else if(policy_type==2)
{
ifstream access_list("access_list.txt");
int max_offset=pow(2, page_size) - 1;
if(access_list.is_open())
{
string line;
int search_index = 0; //time_stamp of the memory accesses
std::vector<int> next_access(table.size(),INT_MAX); //stores when will the tlb/ram entry be next accessed
while(getline(access_list, line))
{
search_index++;
stringstream ss(line);
int search_PID, search_address;
ss >> search_PID;
ss >> search_address;
search_PID = pid_mapping[search_PID];
//Checking memory accesses that will be made after current access
if(search_index>access_index)
{
bool foundall_nextaccesses=true;
for(int i=0;i<table.size();i++)
{
bool found=false;
//if the memory accessed searched/read from file is found in tlb/ram
//update the value of its next access
if(table[i]->pid==search_PID&&(table[i]->virtual_address<=search_address&&table[i]->virtual_address+max_offset>=search_address))
{
found=true;
if(next_access[i]==INT_MAX)
{
next_access[i]=search_index;
}
}
//Next accesses of all the tlb/ram entries have not been found yet
if(next_access[i]==INT_MAX)
foundall_nextaccesses=false;
//If current search found in tlb/ram and next accesses of all tlb/ram entries have not been found yet
if(!foundall_nextaccesses&&found)
break;
}
//Next accesses of all tlb/ram entries found: no more seacrhing needed!
if(foundall_nextaccesses)
break;
}
}
//replace the tlb/ram entry which will be accessed last(after the most time)
int max_next_access=-1,pos=0;
for(int i=0;i<next_access.size();i++)
{
if(max_next_access<next_access[i])
{
pos=i;
max_next_access=next_access[i];
}
}
old_index=pos;
old_entry=table[pos];
table[pos]=new_entry;
}
else
{
printf("Unable to read memory accesses file\n");
}
}
else
{
printf("Undefined replacement strategy\n");
}
return {old_entry, old_index};
}