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 code provided reads the content of file for you and populate the threads information in a dynamic
array of type struct thread. This list of threads is populated for you in the threads. Also, you
have threadCount variable available to see the number of threads that are populated from the input
file. You may add some more members to this data structure if required. If you want to initialize
those additional members, then you can possibly do that during the file read.
2. The main() already contains the code to read threads from input file. However, there is no code to
initialize, execute and synchronize threads. You have to 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.
3. 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.
4. You will need to create and use POSIX pthreads and semaphore(s) to implement the required logic.
5. 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: