Project 02: Process Queue Shell

Overview

The second project is to build a basic shell that serves as a multi-core process queue called pqsh. This program allows the user to enter in a series of commands and then schedules the specified jobs to run on multiple CPU cores as separate processes.

As shown above, the process queue shell has a queue of running jobs (ie. tasks that are actively assigned CPU time), and a queue of waiting jobs (ie. tasks that haven't started yet or have been preempted). Its purpose is to schedule as many running jobs as there are CPU cores using either the FIFO or Round Robin scheduling policies.

Unlike a regular shell, commands in pqsh are not executed right away. Instead, new jobs are added to a waiting queue, where they will be processed by an internal scheduling policy such as FIFO or Round Robin. When there are available resouces (ie. CPUs), the scheduler will move the job from the waiting queue to the running queue. When the job terminates, it will then move to the finished queue.

Working individually, you are to utilize low-level system calls to create this pqsh shell by noon on Saturday, September 28, 2019. More details about this project and your deliverables are described below.

Commands

To interact with the shell, the user has access to two commands:

1. add COMMAND: This command adds the specified COMMAND as a job to the shell's internal waiting queue.

2. status [QUEUE]: This command displays metrics from the internal scheduler (ie. number of jobs in each queue, average turnaround time, and average response time), including the jobs in each of the internal running, waiting, and finished queues (if a QUEUE is specified then only that queue is displayed, otherwise all queues are shown).

Scheduling

The order in which jobs should be executed is determined by one of the following scheduling policies:

1. FIFO: Execute jobs in the order in each they arrival in the process queue.

2. Round Robin: Execute jobs in a round robin fashion.

You must implement both scheduling disciplines along with any accounting and preemption mechanisms required to build these algorithms.

Usage

The full set of pqsh command-line options are shown below:

$ bin/pqsh -h
Usage: ./bin/pqsh [options]

Options:
    -n CORES           Number of CPU cores to utilize
    -p POLICY          Scheduling policy (fifo, rdrn)
    -t MICROSECONDS    Timer interrupt interval
    -h                 Print this help message

The number of CPU CORES and the scheduling POLICY can be specified by the user when the shell is started, but cannot change once it is active. By default, the shell assumes one core and the FIFO scheduling policy.

Here is an example of pqsh running one command using the FIFO scheduler on one CORE:

$ bin/pqsh

PQSH> help
Commands:
  add    command    Add command to waiting queue.
  status [queue]    Display status of specified queue (default is all).
  help              Display help message.
  exit|quit         Exit shell.

PQSH> add bin/worksim 10
Added process "bin/worksim 10" to waiting queue.

PQSH> status
Running =    1, Waiting =    0, Finished =    0, Turnaround =  -nan, Response =  -nan

Running Queue:
  PID COMMAND                        ARRIVAL       START         END
10071 bin/worksim 10                 1568055878.75 1568055878.95          0.00

PQSH> status
Running =    0, Waiting =    0, Finished =    1, Turnaround = 10.00, Response = 00.00

Finished Queue:
  PID COMMAND                        ARRIVAL       START         END
10071 bin/worksim 10                 1568055878.75 1568055878.95 1568055889.19

Here is a video example using of pqsh and the output of its test programs:

Reference Implementation

You can find a reference implementation of pqsh in the following location on the student machines:

/escnfs/home/pbui/pub/bin/pqsh

Feel free to play around with this in order to explore how pqsh should behave.

Deliverables

As noted above, you are to work individually to implement pqsh. You must use (C99) (not C++) as the implementation language for pqsh itself, while any test scripts are to be written in any reasonable scripting language.

Timeline

Here is a timeline of events related to this project:

Repository

To start this project, you must fork the Project 02 repository on GitLab:

https://gitlab.com/nd-cse-30341-fa19/cse-30341-fa19-project02

Once this repository has been forked, follow the instructions from Reading 00 to:

1. Make the repository private.

2. Configure access to the repository.

   Make sure you add all the members of the team in addition to the instructional staff.

Note: Do your work in a separate git branch that can be later merged into the master branch (ie. make a pqsh branch, DO NOT COMMIT OR MERGE TO MASTER).

Documentation

The Project 02 repository includes a README.md file with the following sections:

1. Student: This should be your name and email address.

2. Brainstorming: This should contain your responses to the provided brainstorming questions (optional for this project).

3. Reflection: This should contain your responses to the provided reflection questions.

4. Errata: This should contain a description of any known errors or deficiencies in your implementation.

5. Extra Credit: This should contain a description of any extra credit you attempted or completed.

You must complete this document report as part of your project.

Source Code

As you can see, the base Project 02 repository contains a README.md file and the following folder hierarchy:

project02
    \_ Makefile     # This is the project Makefile
    \_ bin          # This contains the executables
    \_ include      # This contains the header files
    \_ lib          # This contains the libraries
    \_ src          # This contains the C99 source code
    \_ tests        # This contains test scripts and source code

You must maintain this folder structure for your project and place files in their appropriate place.

Compiling

To help you get started, we have provided a Makefile that will build the pq application for you:

$ make                      # Build pq executable
Compiling src/pqsh.o
Compiling src/options.o
Compiling src/process.o
Compiling src/queue.o
Compiling src/signal.o
Compiling src/scheduler.o
Compiling src/scheduler_fifo.o
Compiling src/scheduler_rdrn.o
Compiling src/timestamp.o
Linking lib/libpqsh.a
Linking bin/pqsh

Running

Once you have the pqsh executable, you can run the shell with different number of CORES or with a different scheduling POLICY:

$ ./bin/pqsh -p fifo        # Run shell with FIFO policy

$ ./bin/pqsh -p rdrn -n 2   # Run shell with Round Robin policy and two cores

To help you test your process queue, the bin/worksim script is provided to you. This script is a workload simulator and uou can use it to create a job that simulates a job that runs for a specified duration. For example, to create a job that runs for 10 seconds:

$ ./bin/worksim 10

This script will be useful for testing the different scheduling policies.

Implementation

All of the C99 header files are in the include/pq folder while the C99 source code is contained in the src directory. To help you get started, parts of the project are already implemented:

[x] options.c               # PQSH parsing options (implemented)
[~] pqsh.c                  # PQSH main executable (partially implemented)
[ ] process.c               # PQSH process structure (not implemented)
[ ] queue.c                 # PQSH queue structure (not implemented)
[ ] scheduler.c             # PQSH scheduler structure (not implemented)
[ ] scheduler_fifo.c        # PQSH FIFO scheduler policy (not implemented)
[ ] scheduler_rdrn.c        # PQSH Round Robin scheduler policy (not implemented)
[~] signal.c                # PQSH signal handlers (partially implemented)
[ ] timestamp.c             # PQSH timerstamp (not implemented)

Basically, some of pqsh shell code, signal utilities, and command-line parsing functions are provided to you, but the scheduling and process management functions are not. Each of the functions in the incomplete files above have comments that describe what needs to be done.

You will need to examine these source files and complete the implementation of the shell. To do so, you will first need to implement a basic Process structure and a corresponding Queue structure:

• process.c: This structure is used to keep track of a process in the system (reference at include/pqsh/process.h).

• queue.c: This structure is used to track a list or queue or Process structures. To enable efficient operations to the front and back of the list, the structure maintains pointers to both the head and tail of the queue. Additionally, it has a size attribute that records the number of items in the queue at all times.

• scheduler.c: This contains the main functions required for the shell include the internal operations and command handlers.

• scheduler_{fifo,rdrn}.c: These contain the implementations to the corresponding scheduling policies.

• timestamp.c: This contains the implementation of a function that returns the current time in the form of a double

Testing

To verify the correctness of the Process, Queue, and timestamp functions, three test programs are provided:

$ make test-units

Testing test_process

Testing test_queue

Testing test_timestamp

Likewise, to verify the behavior of your pqsh shell, we have provided you a series of test scripts:

$ make test-scripts

Testing test_fifo_checklist ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Testing test_fifo_multicore ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Testing test_fifo ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Testing test_rdrn_checklist ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Testing test_rdrn_multicore ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Testing test_rdrn ...
Running PQSH commands ... SUCCESS
Verifying PQSH output ... SUCCESS
Verifying PQSH memory ... SUCCESS

Note, you can always run a specific test directory:

$ ./tests/test_fifo.sh      # Run FIFO test script

If necessary, you should not hesitate in create your own additional test programs or scripts to facilitate verification and debugging.

Extra credit

Once you have completed your project, you many extend your implementation of pqsh by performing either (or both) of the following modifications:

1. Readline: Currently, pqsh does not have shell niceties such as tab-completion or history. Use GNU Readline to implement these quality of life improvements.

2. Cleanup: Currently, pqsh does not have a method of clearing a queue. Add a clear command that removes and terminates all processes in a specified queue (ie. clear running removes all processes in the running queue, terminates each process, and frees the allocated memory).

Each of these modifications is worth 1 Point of extra credit each.

Note: Do your work in a separate git branch that can be later merged into the master branch (ie. make a ec-readline or ec-clear branch, DO NOT COMMIT OR MERGE TO MASTER).

Grading

Your project will be graded on the following metrics: