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COMP30023 Project 1
Lock, Lock, …, Deadlock
Out date: March 14, 2022
Due date: No later than 14:59 March 29, 2022 AEDT
Weight: 15% of the final mark
Background
In this project you will familiarise yourself with detection of deadlocks in a multi-process environment.
Please note that you do not need to lock any files to implement this project.
We strongly advise you to start working on the project as soon as possible and read the whole spec before
beginning implementation.
1 Detecting and breaking locks
You will be given a description of running processes and the files they need to execute, where each process
is associated with two files. The first one is the file that the process has locked and the second one is
the file that it is waiting to lock. The goal of your program is to determine whether given the current
resource allocation and requests there is a deadlock or not. Please see Week 2 Lecture 2 on deadlocks
for more information.
If there is no deadlock, you are asked to compute the minimum execution time required for all processes
to finish given the following specification. If a process locked a file, it takes 1 time unit to operate on
this file and release it. If a process requested a file, after a process is given this file, it takes 1 time
unit to operate on this file and release it. Hence, any process takes at least 2 time units to finish. If k
processes have requested the same file, it will take k time units for the processes to finish, where k ≥ 1.
Processes that have locked or requested distinct files can operate in parallel. That is, if two processes
have requested two different files then it will take a total of 1 time unit for the processes to operate on
these files if both files are not locked by other processes.
If there is a deadlock, you are asked to return process(es) that have to be terminated in order to resolve
the deadlock.
2 Program Specification
Your program will be invoked via the command line. It must be called detect and take the following
command line arguments. The arguments can be passed in any order but you can assume that they
will be passed exactly once.
-f filename specifies the path to the file describing requests.
-e is an optional parameter, which when provided requires your code to compute execution time. If this
option is not given, your code should identify presence or absence of deadlocks and which processes
need to be terminated to resolve deadlock(s).
-c is an optional parameter, which when provided invokes your file per process allocation from Section 4.
The file specified by filename contains the processes and their locked and requested resources in the
following format.
Each line of the file corresponds to a process and consists of a space-separated tuple:
process-id space file-id space file-id
1
where the first file-id is the file that the process has locked and the second file-id is the file requested by
the process. You can assume that all process-ids will be distinct integers in the domain of [0, 2
32). You
can assume that all file-ids will be integers in the domain of [0, 2
32).
Example: ./detect -f resources.txt
The detection program is required to determine if there is a deadlock in the current resource allocation.
For example resources.txt with the following information:
0 1 3
1 2 7
describes a system where process 0 has locked file 1 and is waiting for file 3 while process 1 has locked
file 2 and waiting for file 7.
If resources.txt has the following information:
0 1 2
1 2 1
then the system has processes 0 and 1, with locks on files 1 and 2, respectively. In addition, process 0
requested file 2 while process 1 requested file 1. Hence, there is a deadlock.
Each line (including the last) will be terminated with a LF (ASCII 0x0a) control character.
We will not give malformed input (e.g., negative ids for processes and files, non-space delimiters, situations
where more than one process locked the same file).
3 Expected Output
In order for us to verify that your code meets the specification, it should print to standard output (stderr
will be ignored) the following information. You should print each line of the expected output followed
by new line.
To get full marks you will be required to print the whole transcript as described below. However, you
can get marks for each task individually as long as your output for that specific task is correct. For
example, you can get full marks for Task 1 and 2 without having implemented later tasks.
Task 1. Systems statistics You are asked to print the total number of processes and files in the
system (both locked and requested).
Task 2. Execution time (No deadlock) You can assume that there is no deadlock in the file
allocation for this task only. You are asked to print minimum execution time required for all processes
to finish given the specification in Section 1.
Task 3. Deadlock detection Your program should print No deadlocks if there are no deadlocks, or
Deadlock detected if there is at least one deadlock.
Tasks 4,5. Breaking deadlocks If your program returns Deadlock detected, you are also asked to
return a list of processes that need to be terminated to break the deadlock. You should print them on
a separate line, separated by spaces. If there are many processes which can be terminated to break a
particular deadlock, choose the process with the smallest ID.
You will need to print the minimum number of processes that need to be terminated to remove all
deadlocks. If there is more than one process that need to be terminated, separate them by space and
print them in ascending order, sorted by process ID.
Sample output 1
Given resources.txt with the following information:
0 1 2
1 2 1
2
On ./detect -f resources.txt your program should print:
Processes 2\n
Files 2\n
Deadlock detected\n
Terminate 0\n
Sample output 2
Given resources.txt with the following information:
0 1 3
1 2 4
On ./detect -e -f resources.txt your program should print:
Processes 2\n
Files 4\n
Execution time 2\n
since processes can proceed in parallel with each other, with each process taking 2 time units as each is
operating on 2 files sequentially.
4 Challenge task
If a deadlock was detected, you are asked to come up with a transcript that allocates files to processes
in such a way that a deadlock is avoided. That is, you can assume that all resources are available and
no files have been locked yet. Instead, the two file-ids associated with a process in the input file are two
files required for the process to execute. A process can only execute if it obtains both files at the same
time. Once it obtains the files, it locks them and releases at the next time unit. Hence, a file cannot be
allocated to more than one process at any given time. A naive way of allocating files to processes would
be to allocate both files to a process, then, once this process releases them (i.e., at the next time unit),
proceed to allocating files to the next process. This would however lead to a slow execution that does
not have any parallelism. Your task is instead to allocate files to separate processes at the same time
while avoiding deadlocks.
In order for us to evaluate whether your allocation avoids deadlocks, you are asked to print an allocation
transcript in the following format. If a process is allocated its two files, print on a separate line
time space process-id space file-id comma file-id
The order in which the file-ids appear above is up to you. You can assume that the process will
automatically release the files allocated to it at the next time unit, so you do not have to print anything
to release the files. You are also asked to print the total simulation time, i.e., the time when all processes
have been given all the files and released them. Time should start at 0, that is the first line of your
transcript will have 0 as time.
You will be required to explain how your algorithm is more efficient than naive sequential allocation in
a short report.
Sample output 3
Given resources.txt with the following information:
0 1 2
1 2 3
2 3 4
3 4 1
./detect -f resources.txt -c could print:
0 0 1,2\n
0 2 3,4\n
1 1 2,3\n
1 3 4,1\n
Simulation time 2\n
3
Note that with -c your program should not print the output required in Section 3.
5 Marking Criteria
The marks are broken down as follows:
Task # and description Marks
- System statistics 1
- Execution time 3
- Deadlock detection 2
- Breaking deadlocks (1 deadlock) 3
- Breaking deadlocks (> 1 deadlock) 2
- Challenge task (Section 4) 2
- Quality of software practices 1
- Build quality 1
Tasks 1-5. We will run all baseline algorithms against our test cases. You will be given access to half
of these test cases and their expected outputs. Half of your mark for the first 5 tasks will be based on
these known test cases. Hence, we strongly recommend you to test your code against them.
Task 6. The challenge task, as described in Section 4, will be evaluated based on a set of 3 test cases
provided to you and your report. We will use these test cases to compare the Simulation time of
your algorithm (with -c option) with the sequential execution. A scheduling algorithm that results in
a shorter Simulation time over the sequential algorithm on all 3 test cases will be awarded 1.5 marks, - mark for improving on 2/3 test cases and 0.5 marks for improving on 1/3 test cases. We may use a
verification algorithm on your transcript to verify that your allocation is sound (e.g., that same file is not
given to two different processes at the same time and that your simulation time is computed correctly).
You will not be provided with expected outputs for test cases in this task.
Please submit a report explaining your scheduling algorithm and why it performs better than the sequential
one. Reports longer than 50 words will automatically get 0 marks. Hence, ensure that you get - or less words when you run wc -w report.txt. The report should be in ASCII format. The report
will be marked only if your algorithm improves simulation time on at least one test case.
Task 7. Quality of software practices Factors considered include quality of code, based on the
choice of variable names, comments, indentation, abstraction, modularity, and proper use of version
control, based on the regularity of commit and push events, their content and associated commit
messages (e.g., repositories with a single commit and push, non-informative commit messages will lose
0.5 mark).
Task 8. Build quality Running make clean && make -B && ./detect <command line arguments>
should execute the submission. If this fails for any reason, you will be told the reason, and be allowed
to resubmit (with the usual late penalty).
A 0.5 mark penalty will be applied if compiling using“-Wall”yields a warning or if your final commit
contains detect, any other executable or .o files (see Practical 2). Executable scripts (with .sh
extension) are excepted.
The automated test script expects detect to exit/return with status code of 0 (i.e., it successfully runs
and terminates).
We will not give partial marks or allow code edits for either known or hidden cases without applying
late penalty (calculated from the deadline).
4 - Submission
All code must be written in C (e.g., it should not be a C-wrapper over non C-code) and cannot use
any external libraries. Your code will likely rely on data structures for managing processes and memory.
You will be expected to write your own versions of these data structures. You can reuse the code that
you wrote for your other individual projects if you clearly specify when and for what purpose you have
written it (e.g., the code and the name of the subject, project description and the date, that can be
verified if needed). You may use standard libraries (e.g., to print, read files, sort, parse command line
arguments1
etc.). Your code must compile and run on the provided VMs and produce deterministic
output.
The repository must contain a Makefile which produces an executable named“detect”, along with all
source files required to compile the executable. Place the Makefile at the root of your repository, and
ensure that running make places the executable there too. Make sure that all source code is committed
and pushed. Executable files (that is, all files with the executable bit which are in your repository)
will be removed before marking. Hence, ensure that none of your source files have the executable bit.
For your own protection, it is advisable to commit your code to git at least once per day. Be sure to
push after you commit. The git history may be considered for matters such as special consideration,
extensions and potential plagiarism. Your commit messages should be a short-hand chronicle of your
implementation progress and will be used for evaluation in the Quality of Software Practices criterion.
You must submit the full 40-digit SHA1 hash of your chosen commit to the Project 1 Assignment
on LMS. You must also push your submission to the repository named comp30023-2022-project-1
in the subgroup with your username of the group comp30023-2022-projects on gitlab.eng.unimelb.
edu.au. You will be allowed to update your chosen commit. However, only the last commit hash
submitted to LMS before the deadline will be marked without late penalty.
You should ensure that the commit which you submitted is accessible from a fresh clone of your repository.
For example (below … are added for aesthetic purposes to break the line):
git clone https://gitlab.eng.unimelb.ed…<username>/ …
… comp30023-2022-project-1
cd comp30023-2022-project-1
git checkout <commit-hash-submitted-to-lms>
Late submissions will incur a deduction of 2 mark per day (or part thereof).
Extension policy: If you believe you have a valid reason to require an extension, please fill in the form
accessible on Project 1 Assignment on LMS. Extensions will not be considered otherwise. Requests for
extensions are not automatic and are considered on a case by case basis. - Testing
You have access to several test cases and their expected outputs. However, these test cases are not
exhaustive and will not cover all edge cases. Hence, you are also encouraged to write more tests to
further test your own implementation.
Testing Locally: You can clone the sample test cases to test locally, from:
comp30023-2022-projects/project-1.
Continuous Integration Testing: To provide you with feedback on your progress before the deadline,
we have set up a Continuous Integration (CI) pipeline on Gitlab. Though you are strongly encouraged
to use this service, the usage of CI is not assessed, i.e., we do not require CI tasks to complete for a
submission to be considered for marking.
Note that the test cases which are available on Gitlab are the same as the set described above.
The requisite .gitlab-ci.yml file has been provisioned and placed in your repository, but is also available
from the project-1 repository linked above. Please clone, commit and push to trigger.
1https://www.gnu.org/software/…
5 - Getting help
Please see Project 1 Help module on LMS. - Collaboration and Plagiarism
You may discuss this project abstractly with your classmates but what gets typed into your program
must be individual work, not copied from anyone else. Do not share your code and do not ask others
to give you their programs. Do not post your code on subject’s discussion board Ed. The best way to
help your friends in this regard is to say a very firm“no”if they ask to see your program, pointing out
that your“no”, and their acceptance of that decision, are the only way to preserve your friendship. See
https://academicintegrity.uni… for more information.
Note also that solicitation of solutions via posts to online forums, whether or not there is payment
involved, is also Academic Misconduct. You should not post your code to any public location (e.g.,
github) until final subject marks are released.
If you use any code not written by you, you must attribute that code to the source you got it from (e.g.,
a book or Stack Exchange).
Plagiarism policy: You are reminded that all submitted project work in this subject is to be your
own individual work. Automated similarity checking software may be used to compare submissions. It
is University policy that cheating by students in any form is not permitted, and that work submitted for
assessment purposes must be the independent work of the student concerned.
Using git is an important step in the verification of authorship.
