LE/EECS **21 – Operating System Fundamentals
Winter 2024—Section N
Programming Assignment 2
Submission Deadline: March 28, 2024 before 16:59
Objectives
In this assignment we will try to practice the concepts such as: multithreading, synchronization with
semaphores, deadlocks and starvation.
Permitted similarity threshold for this assignment is 70%.
General Assignment Notes
When writing and submitting your assignments follow these requirements:
• Name your source code file as: your YorkU student number, an underscore, 'a' (for 'assignment',
then the assignment number in two digits. For example, if the user 100131001 submits Assignment
2, the name should be: 100131001_a02.c.txt. No other file name format will be accepted. We
require the .txt extension in the end because eClass does not allow .c extension.
• Use the same naming scheme for the assignment title when submitting the assignment to the
eClass; do not add “.c.txt” in the title.
• For this assignment you must use C99 language syntax. Your code must compile using make
without errors and warnings. You are provided with a makefile and instructions on how to use
it. If you use that makefile to compile the code, then you don’t have to do anything special to select
C99. The makefile that we have provided doesn’t let your program compile if there are warnings;
hence, make sure no warnings or errors at all.
• Test your program thoroughly with the gcc compiler in a Linux environment. Make you’re
your gcc version is at least the same as university red servers. This can be verified by running the
command “gcc --version” in Linux shell.
• If your code does not compile, then you will get zero. Therefore, make sure that you have removed
all syntax errors from your code.
Marks will be deducted from any question(s) where these requirements are not met.
WARNING
Follow the assignment instructions to the letter in terms of the file names and function names, as
this assignment will be auto graded. If anything is not as per description, the auto grading will fail, and
your assignment will be given a mark of 0.
You program must terminate normally on the provided test case; if it does not terminate normally then
auto-grader will get empty output and it will be awarded zero.
Synopsis
In this assignment, our process will create multiple threads at different times. These threads may have
different start_time but there is no lifetime. Each thread after its creation runs a small critical section
and then terminates. All threads perform same action/code. Most of the code such as reading the input
file, creating the threads etc. is provided. Your task is to implement following synchronization logic with
the help of POSIX pthreads and semaphores:
• Only one thread can be in its critical section at any time in this process.
• The first thread, in terms of creation time, enters first in its critical section.
• After that threads are permitted to perform their critical section based on their ID.
o Threads are given IDs in the format txy where x and y are digits (0-9). Thread IDs are
unique. Threads may have same or different start_time. Thread entries in the input file can
be in any order.
o The “y” in thread IDs thus will either be an even digit or odd digit.
o After the first thread, the next thread that will be permitted to perform its critical section
must be the one in which “y” is different i.e. if “y” was even in first thread then in the next
it must be odd or vice versa.
o For the rest of the process, you must follow the same scheme i.e. two threads with odd “y”
or even “y” can not perform critical section simultaneously.
• Since synchronization may lead to deadlock or starvation, you have to make sure that your solution
is deadlock free i.e. your program must terminate successfully, and all the threads must perform
their critical section.
• One extended form of starvation will be that towards the end, we have all odd or all even processes
left, and they are all locked because there are no other type (odd/even) of threads left. Once the
process reaches to that stage, you must let them perform their critical section to avoid starvation
and progress towards the end of the process. In the screen shot on the next page, you will notice
that t07, t05 and t01 perform their critical section without any even number thread separating them
because there are no more even number threads left. However, you must make sure that there
are no other threads coming in future which could help avoid this situation. If there is chance
for more threads coming, then you will hold this till then. For example, in the screenshot on
the next page, this started happening at t=20 which is the creation time of the last thread in
our input file.
Description
For this assignment, you are provided a skeleton code in the file student_code.c. Some functions are
completely implemented, and some are partially implemented. Additionally, you can write your own
functions if required. Complete the program as per following details so that we can have functionality as
described in the Synopsis above. Write all the code in single C file. DO NOT forget to rename your C
code file appropriately when submitting:
1. The readFile(), if called with filename and struct thread pointer as arguments, can read the
content of file for you and populate the threads’ information in a dynamic array of type struct
thread. Such a pointer threads is provided there in main() and you can use it. readFile()returns
the number of threads read from the file and you must connect it with the threadCount variable
provided in the main().
2. You may add some more members to struct thread if required. If you want to initialize those
additional members, then you can possibly do that in readFile().
3. The main() already contains some code and hints to guide you. However, there is no call to
readFile() or code to initialize, execute and synchronize threads. You must perform these tasks in
a suitable way there. startClock() invocation as given in main() is required to initiate the
program’s internal clock, so do not remove it.
4. The threadRun() function also contains the code that a thread must run. However, the
synchronization logic (entry/exit section) is missing. Add the suitable code before and after the
critical section.
5. You will need to create and use POSIX pthreads and semaphore(s) to implement the required logic.
6. The image below shows the expected output for the sample input file (sample2_in.txt) provided with
this assignment. In this output when there are multiple threads finishing (or may be starting) at the
same time, e.g. at t=5 both t02 and t07 are finished, then their order may switch and may be different
than their critical section order, because start/finish is out of critical section and unsynchronized.
However, the critical section order, e.g. in t=5 both t02 and t07 perform their critical section, must
always be as per our synchronization requirement. Also, you have to make sure that a thread must
be started at its creation time as per the input file i.e. “is started” message of thread must have the
same time stamp as mentioned in the input file:
7. Do not change the code in the functions: logStart(), logFinish(), startClock(),
getCurrentTime(). Also, do not change the signature of any of the functions that are given in the
code provided.

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