COMP3520 Assignment 1 2023
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COMP3520 Operating Systems Internals
Assignment 1 – Synchronization
General Instructions
This assignment is about synchronization. It consists of two compulsory tasks:
1. Write a multithreaded Pthread program to solve the synchronization problem as
described in the section “Stylish Hairdressing Salon”; and
2. Answer the assigned discussion document questions (which are provided in a
separate document).
This assignment is an individual assignment. Whilst you are permitted to discuss this
assignment with other students, the work that you submit must be your own work. You
should not incorporate the work of other students (past or present) or Artificial
Intelligence (AI) tools into your source code or discussion document.
You will be required to submit your discussion document to Turnitin for similarity
checking as part of assignment submission. The examiner may use other similarity
checking tools in addition to Turnitin. Your source code may also be checked.
Submit your source code and report to the appropriate submission inboxes in the
COMP3520 Canvas website.
The Problem: Stylish Hairdressing Salon
In Stylish Hairdressing Salon, there are K barbers. Each time, a barber takes a minimum
of T1 units of time and a maximum of T2 units of time to service one customer.
The salon has N waiting chairs. When a customer arrives and if there are free waiting
chairs, he/she takes a ticket and then sits on a waiting chair, waiting for their ticket
number to be called. If all the waiting chairs are occupied, however, the newly arrived
customer simply leaves (and vanishes). The tickets are numbered from 1 to N and
initially placed in ascending order. Customers always take a ticket from one end and
return the ticket to the other end after being called. In this way, the ticket numbers are
always maintained in a perfect cyclic order.
There is one shop assistant looking after the customers. When a barber becomes
available, the assistant will call one waiting customer to get haircut by that barber.
Customers will be called in a first-come-first-served order. Note that customers are not
allowed to choose barbers in this salon.
This is a synchronization problem. To solve this problem, you need to consider various
situations. For example,
• when there are no customers and all barbers are waiting;
• when all barbers are busy and customers are waiting; and
• how to assign customers to a specific barber when that barber is available.
In your implementation, only barbers determine how long it takes to service each
customer. The program will terminate only after all barbers have done their work. You
need to write three routines, i.e., customer, barber and assistant, in addition to main.
COMP3520 Assignment 1 2023
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To implement synchronization between various threads, you may use Pthread mutexes,
and condition variables. However, you must not use any other type of
synchronization mechanism.
Your program needs to ask the user to enter the following parameters:
• M: the total number of customers;
• K: the number of barbers working in the salon;
• N: the total number of waiting chairs in the salon;
• T1: the minimum number of units of time for a barber to service a customer;
• T2: the maximum number of units of time for a barber to service a customer;
• T3: the minimum number of units of time between two customer arrivals; and
• T4: the maximum number of units of time between two customer arrivals.
To check whether your program functions properly, your program must print the
statements described below.
Each Customer thread must print the following status messages wherever appropriate:
• “Customer [id]: I have arrived at the barber shop." – New customer with
customer id arrives
• "Customer [id]: Oh no! All seats have been taken and I'll leave now!" – All
waiting chairs are occupied and the customer leaves
• "Customer [id]: I'm lucky to get a free seat and a ticket numbered n" – Take a
ticket numbered n and sit on a free waiting chair
• “Customer [id]: My ticket number n has been called. Hello, Barber [id].” – To
get haircut next by Barber [id]
• “Customer [id]: Well done. Thanks Barber [id]. Bye!” – Get haircut done and
leave
Each Barber thread must print the following status messages wherever appropriate:
• “Barber [id]: I’m now ready to accept a customer.” – Wait for a new customer
• “Barber [id]: Hello, Customer n.” – To service the assigned customer with a
ticket number n
• “Barber [id]: Finished cutting. Good bye Customer n.” – Finished servicing
Customer n
• “Barber [id]: Thanks Assistant. See you tomorrow!” – Finished working for
the day and leaves
The Assistant thread must print the following status messages wherever appropriate:
• “Assistant: I’m waiting for customers.” – Wait for customers
• “Assistant: I’m waiting for a barber to become available.” – Wait for barber
• “Assistant: Assign Customer n to Barber [id].” – Assign Customer n to Barber
[id]
• “Assistant: Hi barbers. We’ve finished the work for the day. See you all
tomorrow!” – Call for all barbers to finish and leave
Note that in the above messages, Customer n is the customer with a ticket numbered n,
and the ticket number n may not be equal to the customer’s [id].
When all customers have been serviced, the main thread must print the following status
message and then terminate:
• “Main thread: All customers have now been served. Salon is closed now.”
COMP3520 Assignment 1 2023
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Additional Requirements
Source Code
Your solution must be implemented in the C language.
Your source code needs to be properly commented and appropriately structured to
allow another programmer who has a working knowledge of C to understand and easily
maintain your code.
You need to include a well-structured and properly commented makefile that allows for
the compilation of your source code using the make command on the School of
Computer Science servers.
Testing and Debugging
You are responsible for testing and debugging your source code.
It is crucial that you ensure that the source code you submit compiles correctly on the
School of Computer Science servers and that the resulting binary functions as intended.
If you submit source code that cannot be compiled on the School servers, marks will be
heavily deducted.
Discussion Document
You are required to answer all assigned questions in a separate written document. The
questions and requirements specific to the discussion document will be provided in a
separate document.
Other Matters
Marking criteria for the source code and discussion document will be provided
separately.
To maximize your chances of realizing your full potential in COMP3520, please start
work on this assignment promptly.