Exercise $3$: Using High and Low Priority Queues:

Background information:

Computing devices like laptops and smartphones may have multiple computing cores, which allow us to run multiple programs at once. But what happens when the number of programs that we want to run is more than the number of cores in our device? For example, what if we want to run $8$ programs on a device with only $2$ CPU cores? Job scheduling helps the device to run the most important programs first. Imagine that each program we want to run submits a job request to the operating system before it is actually run. Those jobs are stored in either a high$-$priority queue or a low$-$priority queue, depending on how important the program is$.$ For example, processes that are fundamental to how the device operates $($e$.$g$.$ displaying things to the screen, dealing with system input and output$)$ have a higher priority than user$-$installed applications $($e$.$g$.$ web browsers, music playing app, calculator app$).$ At any given time, jobs waiting in the high$-$priority queue will be executed first, in the order that they were requested in$.$ If there are no high$-$priority jobs waiting to be executed, then the jobs in the low$-$priority queue can be executed.

Problem:

Download lab$6\_$priority.py from eClass, and save in the same folder as your other lab files. This file contains a Job class definition, as well as two functions that have already been completed for you $($get$\_$job$(),$ and process$\_$complete$()).$ Read the comments for this code to understand what it does Add code to the main$()$ function in this file so that every time a new job is created $($i$.$e$.$ every time get$\_$job$()$ is called$),$ that job object is enqueued to the appropriate queue:

high$\_$priority$\_$queue or low$\_$priority$\_$queue.

Complete the main$()$ function so that whenever a process has finished $($indicated when

process$\_$complete$()$ returns True$),$ a new process is started by dequeuing a job from the

appropriate queue. i$.$e$.$ If there is at least one job in the high$-$priority queue, it should be dequeued and assigned to the current$\_$job variable. However, if the high$-$priority queue is empty and there is at least one job in the low$-$priority queue, then it should be dequeued and assigned to the current$\_$job variable. If a job has been successfully dequeued from either queue, the process$\_$running variable should be set to True.

lab$6\_$priority.py

import random

from queues import CircularQueue

class Job:

def $\_\_$init$\_\_($self$,$ priority $=0,$ process$\_$name $=$ None$)$:

$\text{'}\text{'}\text{'}$

Object for job description of various types

:param priority: $0$ for low and $1$ for high priority

:param process$\_$name: Description of the process $($optional$)$

$\text{'}\text{'}\text{'}$

self.$\_\_$id $=$ random.randint$(1,1000)$

self.$\_\_$priority $=$ priority

if process$\_$name is None:

if self.high$\_$priority$()$:

self.$\_\_$process$\_$name $=$ random.choice$([\text{'}[$OS$]$ File Write', $\text{'}[$OS$]$ File Read', $\text{'}[$OS$]$ Display'$])$

else:

self.$\_\_$process$\_$name $=$ random.choice$([\text{'}[$USER$]$ Browser', $\text{'}[$USER$]$ Music', $\text{'}[$USER$]$ Calculator'$])$

def high$\_$priority$($self$)$:

$\text{'}\text{'}\text{'}$

Priority of the job

:return: True if process of high priority

$\text{'}\text{'}\text{'}$

return self.$\_\_$priority $==1$

def process$\_$name$($self$)$:

$\text{'}\text{'}\text{'}$

Process name of the job

:return: returns the process name for the job

$\text{'}\text{'}\text{'}$

return self.$\_\_$process$\_$name

def $\_\_$str$\_\_($self$)$:

return $\text{'}\{$:$<mn\; id="EditorElement\_191062">1</mn><mn\; id="EditorElement\_191063">5</mn><mi\; id="EditorElement\_191064">\}</mi>$ : $\{$:$<mn\; id="EditorElement\_191071">2</mn><mn\; id="EditorElement\_191072">0</mn><mi\; id="EditorElement\_191073">\}</mi>$

$\{$:$<mn\; id="EditorElement\_191078">1</mn><mn\; id="EditorElement\_191079">5</mn><mi\; id="EditorElement\_191080">\}</mi>$ : $\{$:$<mn\; id="EditorElement\_191087">2</mn><mn\; id="EditorElement\_191088">0</mn><mi\; id="EditorElement\_191089">\}</mi>$

$\{$:$<mn\; id="EditorElement\_191094">1</mn><mn\; id="EditorElement\_191095">5</mn><mi\; id="EditorElement\_191096">\}</mi>$ : $\{$:format$(\text{'}$ID$\text{'},$self.$\_\_$id$,$ 'Process Name',self.$\_\_$process$\_$name, 'Priority','HIGH' if self.$\_\_$priority $==1$ else 'LOW' $)$

def get$\_$job$()$:

$\text{'}\text{'}\text{'}$

Return a job type $,$ trying to simulate a queueing process for the CPU

:return: Returns the Job Object or none

$\text{'}\text{'}\text{'}$

if random.random$()<mtext\; id="EditorElement\_191395"></mtext><mn\; id="EditorElement\_191396">.</mn><mn\; id="EditorElement\_191397">5</mn>$:

return Job$($priority$=1)$

if random.random$()<mtext\; id="EditorElement\_191455"></mtext><mn\; id="EditorElement\_191456">.</mn><mn\; id="EditorElement\_191457">9</mn>$:

return Job$($priority$=0)$

return None # the no job

def process$\_$complete$()$:

$\text{'}\text{'}\text{'}$

Returns a boolean value telling if the current process is complete executing or not

:return: True$/$False depending the process is complete or not

$\text{'}\text{'}\text{'}$

if random.random$()<mtext\; id="EditorElement\_191739"></mtext><mn\; id="EditorElement\_191740">0</mn><mn\; id="EditorElement\_191741">.</mn><mn\; id="EditorElement\_191742">5</mn>$:

return True

return False

def main$()$:

process$\_$running $=$ False # tells the state of the processor True if a process is running

current$\_$job $=$ None

high$\_$priority$\_$queue $=$ CircularQueue$(1000)$

low$\_$priority$\_$queue $=$ CircularQueue$(1000)$

# we will run our computer for $10$ time steps

time$\_$steps $=10$

for t in range$($time$\_$steps$)$:

print$("$######## RUN : $\{\}$ ########

$".$format$($t$+1))$

job $=$ get$\_$job$()$ # get a job

if job:

print$("$Job $\{\}$ generated

$".$format$($job$.$process$\_$name$()))$

# Put the job in the appropriate queue

########################

### ENTER YOUR CODE ####

########################

########################

#### END OF CODE ######

########################print$("$Jobs waiting in High Priority Queue :$\{\}".$format$($high$\_$priority$\_$queue.size$()))$