class OptimalPageReplacement:
# Default constructor
def __init__(self, page_sequence, num_of_frames):
# Initializing a list attribute containing the sequence of pages
self.sequence = []
self.sequence = page_sequence
# Initializing the variable holding the number of page faults
self.page_fault = 0
# Initializing the variable telling us the number of frames to use
self.frame_size = num_of_frames
# Creating the queue data structure to be used
self.queue = Queue()
# Function used to execute the logic for optimal page replacement
def run(self):
# Iterating through pages getting the values indexes of those values
for position, i in enumerate(self.sequence):
# Checking to see if there is place to insert a page in a frame
# If there is space
if self.queue.size() < int(self.frame_size):
# Next we check if the page is already present in the frames
try:
position = self.queue.find(i)
# If the page is present, just display the status of the frames and the pages in them
self.display(i)
except ValueError:
# We insert the page into the queue since there is place
self.queue.enqueue(i)
# Display the current status fo the frames
self.display(i)
# Incrementing page fault as we are inserting an page into the frame
self.page_fault += 1
# If there is no space
else:
# Next we check if the page is already present in the frames or not
try:
position = self.queue.find(i)
# if the page is already present then, just display the current status of the frames and the pages
self.display(i)
except ValueError:
# We get the position of the page in the list
page_position = position
# We call the check future use function to check for the page that is used the least in the future
self.check_future_page_use(page_position)
# Then we insert the new page to the frames
self.queue.enqueue(i)
# Display the current status of the frames
self.display(i)
# Incrementing the number of page faults because we are inserting a page into the frames
self.page_fault += 1
# Function used to display the current status of the frames and their values
def display(self, page):
# Initializing the status string variable
status_string = page + ": <"
# Iterating through the frames
for i in range(int(self.frame_size)):
# Checking if there is a value at the frame
try:
# If there is a value then the status string is updated
value = self.queue.get(i)
status_string += value + ", "
# if there isn't a value then an index error is thrown and the status string is updated
except IndexError:
status_string += " " + ", "
# Finally we remove the last comma from status string and adding the closing angular bracket instead
status_string = status_string[0:len(status_string) - 2]
status_string += ">"
# Printing the status string
print(status_string)
# Function to used to check for pages that aren't used in the future as much
def check_future_page_use(self, page_index):
# Creating a dictionary to hold the details of the pages and their future usage
page_usage_details = dict()
# Using the page_index + 1 we convert the rest of the list into a string
temp_string_one = str(self.sequence[page_index + 1:len(self.sequence)])
for i in self.queue.items:
# Finding the first occurrence of the page already present in the queue
position = temp_string_one.find(i)
# If it not found then you store the page and and the position as zero
if position == -1:
position = None
page_usage_details[i] = position
# If it found then you store the page and the position that is returned
else:
page_usage_details[i] = position
print("future pages and their positions ", page_usage_details)
# Counter to keep track of how locations we have found
counter = 0
# Iterating through the dictionary
for key, value in page_usage_details.items():
# If we have found a location
if value is not None:
counter += 1
# Checking the counter to see if type of situation we have got
# if we have the position of all the pages already in the frame
if counter == self.queue.size():
# Then we get the furthest position in the string
max_key = max(page_usage_details.keys(),
key=(lambda key: page_usage_details[key]))[0]
# remove the page with the furthest position value
self.queue.remove(max_key)
# if we have found one page that is not used in the future
elif counter == self.queue.size() - 1:
# find the page with the none value and then remove it
for key, value in page_usage_details.items():
if value is None:
self.queue.remove(key)
break
# if there are two or more pages that cannot be found use FIFO
elif counter >= self.queue.size() - 2:
# Creating a temporary dictionary
temp_dict = dict()
# we take the first half of the sequence from teh new value found for this condition
temp_string_two = str(self.sequence[0:page_index])
# among the none values we see has the lowest occurrence
for key, value in page_usage_details.items():
# if the value is none find its position in the temp string two
if value is None:
# finding the position of the value
position = temp_string_two.rfind(key)
# adding the page and its position to the temporary dictionary
temp_dict[key] = position
# After deciding which page to replace using FIFO we replace the page
self.queue.remove(
min(temp_dict.keys(), key=lambda key: temp_dict[key]))
class FirstInFirstOut:
# Default constructor
def __init__(self, page_sequence, num_of_frames):
# Initializing a list attribute of page sequences
self.sequence = page_sequence
# Initializing the number of page faults
self.page_fault = 0
# Initializing the number off frames
self.frame_size = num_of_frames
# Creating a queue to use
self.queue = Queue()
# Function used to execute the logic of fifo
def run(self):
# Iterating through the page sequence
for i in self.sequence:
# Next we check if the queue is full or not
if self.queue.size() < int(self.frame_size):
# Checking if the page is present in the queue or not
try:
position = self.queue.find(i)
# Display the status of the queue
self.display(i)
except ValueError:
# if queue is not full add the page to the queue
self.queue.enqueue(i)
# display the current status of the queue
self.display(i)
# If it is not present then increment the page fault
self.page_fault += 1
# If the queue is full pop the first page and add new page at the end
else:
# Checking if the page is present in the queue or not
try:
position = self.queue.find(i)
# Display the status of the queue
self.display(i)
except ValueError:
# Pop the page in front of the queue
self.queue.dequeue()
# Insert the new page to the queue
self.queue.enqueue(i)
# Display the status of the queue
self.display(i)
# If it is not present then increment the page fault
self.page_fault += 1
# function used to display the frame and the pages in them
def display(self, page):
# Initializing the status string
status_string = page + ": <"
# Iterating through the frames
for i in range(int(self.frame_size)):
# Checking if there is a value at the frame
try:
# If there is a value then the status string is updated
value = self.queue.get(i)
status_string += value + ", "
# if there isn't a value then an index error is thrown and the status string is updated
except IndexError:
status_string += " " + ", "
# Finally we remove the last comma from status string
status_string = status_string[0:len(status_string)-2]
status_string += ">"
# Printing the status string
print(status_string)
