CS204 Take Home Exam 5 – Waiting for the Worms Solution

DISCLAIMER:
Your program should be a robust one such that you have to consider all relevant user mistakes and extreme cases; you are expected to take actions accordingly!
Introduction
The aim of this assignment is to practice on multithreaded operations and particularly producer-consumer patterns. In this assignment, you will simulate a system where encrypted files are supplied by two producer threads to a main queue and three consumer threads dequeue these file names and decrypt these files of given names. Let’s see if cryptography is fun!
Input to Your Program
Input to your program will be several encrypted files, which are given in the assignment bundle. Before launching your producer and consumer threads, your main function will read the names of all files the program will use. Typing only a dash “-” will stop receiving file names. Your program will not immediately check whether the file names are correct or not; your consumer threads will check it when they dequeue a file name from the main queue.
Format of the Input Files
Threads and what they do
After that, you need to launch 2 producer and 3 consumer threads from the main thread. Do not forget that producer threads need access to the file names.
Producer threads: These threads have one simple duty: They need to get a file name from the structure of your choice and place it into the main queue. Make sure that you understand that the file name structure and the main queue are shared by multiple threads so you need to take some precautions before and after using each of them :) We all know that this precaution is called a “mutex”. Make sure to delete file names from your structure so that they are not placed into the queue multiple times.
Producer threads need to sleep before doing some work. This sleep time will be randomly calculated each time by your program. You can use the RandGen library given to you for picking a random integer between 1000 and 4000, in milliseconds. The producer threads will terminate when there are no more files left to enqueue to the main queue.
Consumer threads: These threads love sleeping as well, as we all do. They sleep for a random time between 2500 to 3500 milliseconds before trying to do anything.
These threads will first try to dequeue a file name from the main queue. Bear in mind that trying to dequeue an empty queue will result in a crash. So, always check its emptiness beforewards.
If the dequeuing is successful (i.e, the queue is not empty), the thread will open the file, decrypt it and write the result to another file. Details of the decryption algorithm are discussed in the following sections. If the file name is not valid, then the thread will print an error message and will not dequeue another item immediately (i.e, it will repeat the process which starts with sleeping)
All the actions that your threads could or could not take should be written to the console. Sample runs provide examples for the outputs that you should produce. Do not forget that cout is an object that you share between threads, hence you should use it with care, as well :)
A very basic string queue implementation is given to you with this THE bundle. You must use it, without changing anything. Note that this queue is of unlimited size.
Caesar’s Cipher

Caesar’s Cipher pattern with shift = +3
In cryptography, Caesar’s cipher is one of the simplest and most widely known encryption techniques. It is a type of substitution cipher in which each letter in the plaintext is replaced by a letter some fixed number of positions up or down the alphabet.
This method is circular, which means that ‘z’ encrypted with a shift of +5 would become ‘e’ and
‘c’ encrypted with a shift of -4 would become ‘y’.
In this assignment, you are given 15 encrypted files. The original files (also the encrypted versions that you have) do not contain any uppercase letters and only the lowercase letters are ciphered with Caesar's method. The files contain whitespaces and other characters such as punctuations, but these characters are not encrypted and copied as they are, so no need to deal with them.
You need to hack the files and produce their originals. The problem is: We do not know what
other might be -20. So, we need a way to guess the shift of the encrypted file :/
Disclaimer: The originals of all files given to you have the most common letter as ‘e’ :)
I see Mutexes
Critical information accessed by threads always has the problem of validation faults. What do you think will happen if your thread K is stopped by the operating system when K had read an item from the queue but had not deleted it yet? Two consumer threads would read the same item and do the decryption multiple times. This is not the worst case. Afterwards, they would try to delete the same node twice and crash the program :/ Now, you got the spirit!
Any resource that can be reached by threads and cannot be used in an atomic way should be restricted with mutexes. Examples of such situations in this assignment are: (i) access to the file name structure, (ii) access to the main queue, (iii) printing to the console.
In order not to have inefficiencies, use seperate mutexes for each resource. Making another thread wait for the dequeuing just because you are printing something is not fair!
Another important point is that, make sure you lock the minimum amount of necessary operations with mutexes. Lock the mutexes right before your thread starts accessing a mentioned resource and unlock it as soon as it is done dealing with that resource.
Output Files
Input files are given to you with .txt extension. The output files should contain the decrypted version of the corresponding input file and should end with “_decrypted.txt”. As an example: a decrypted version of “file1.txt” should be written to a file named “file1_decrypted.txt”.
Sample Runs
Below, we provide some sample runs of the program that you will develop. The italic and bold phrases are the standard inputs (cin) taken from the user (i.e., like this). You have to display the required information with the same words as here.
We are not giving you the resulting output files. You can immediately understand that you are doing it right once you see some English text as the result (although they are meaningless :D)
The shift amounts are removed from the outputs (--), apart from the one of file3.txt . Those shift amounts should be found by your program using the most common letter property mentioned above. Do not try to hardcode anything as your programs will be tested with different files.
Sample Run 1
Please enter a file name: file3.txt
Please enter a file name: file4.txt
Please enter a file name: file5.txt
Please enter a file name: asdasd
Please enter a file name: --
Please enter a file name: *
Please enter a file name: -
Producer Thread - 1 starts sleeping for 1715 milliseconds
Producer Thread - 2 starts sleeping for 1003 milliseconds
Consumer Thread - 1 starts sleeping for 2501 milliseconds
Consumer Thread - 2 starts sleeping for 2501 milliseconds
Consumer Thread - 3 starts sleeping for 2501 milliseconds
Producer Thread - 2 is now enqueuing "*"
Producer Thread - 2 starts sleeping for 2691 milliseconds
Producer Thread - 1 is now enqueuing "--"
Producer Thread - 1 starts sleeping for 2865 milliseconds
Consumer Thread - 1 is now handling "*"
Consumer Thread - 2 is now handling "--"
Consumer Thread - 1 cannot process "*", there is no such file!
Consumer Thread - 3 cannot find any file to dequeue for now.
Consumer Thread - 2 cannot process "--", there is no such file!
Consumer Thread - 1 starts sleeping for 3064 milliseconds
Consumer Thread - 3 starts sleeping for 3064 milliseconds
Consumer Thread - 2 starts sleeping for 3064 milliseconds
Producer Thread - 2 is now enqueuing "asdasd"
Producer Thread - 2 starts sleeping for 1580 milliseconds
Producer Thread - 1 is now enqueuing "file5.txt"
Producer Thread - 1 starts sleeping for 1783 milliseconds
Producer Thread - 2 is now enqueuing "file4.txt"
Producer Thread - 2 starts sleeping for 3426 milliseconds
Consumer Thread - 1 is now handling "asdasd"
Consumer Thread - 3 is now handling "file5.txt"
Consumer Thread - 2 is now handling "file4.txt"
Consumer Thread - 1 cannot process "asdasd", there is no such file!
Consumer Thread - 2 is done handling "file4.txt" with a shift of -- and written the result to
"file4_decrypted.txt"
Consumer Thread - 1 starts sleeping for 2693 milliseconds
Consumer Thread - 3 is done handling "file5.txt" with a shift of -- and written the result to
"file5_decrypted.txt"
Consumer Thread - 2 starts sleeping for 2693 milliseconds
Consumer Thread - 3 starts sleeping for 2693 milliseconds
Producer Thread - 1 is now enqueuing "file3.txt" Producer Thread - 1 starts sleeping for 1695 milliseconds Producer Thread - 1 cannot find any file to enqueue, joining...
Consumer Thread - 1 is now handling "file3.txt"
Consumer Thread - 1 is done handling "file3.txt" with a shift of 13 and written the result to
"file3_decrypted.txt"
Consumer Thread - 2 cannot find any file to dequeue, joining...
Consumer Thread - 1 starts sleeping for 3309 milliseconds Consumer Thread - 3 cannot find any file to dequeue, joining... Producer Thread - 2 cannot find any file to enqueue, joining...
Consumer Thread - 1 cannot find any file to dequeue, joining...
All threads have joined with main, exiting... Press any key to continue . . .
Sample Run 2
Please enter a file name: -
Producer Thread - 1 starts sleeping for 2692 milliseconds
Producer Thread - 2 starts sleeping for 1003 milliseconds
Consumer Thread - 1 starts sleeping for 2501 milliseconds
Consumer Thread - 2 starts sleeping for 2501 milliseconds
Consumer Thread - 3 starts sleeping for 2501 milliseconds
Producer Thread - 2 cannot find any file to enqueue, joining...
Consumer Thread - 1 cannot find any file to dequeue, joining...
Consumer Thread - 2 cannot find any file to dequeue, joining...
Consumer Thread - 3 cannot find any file to dequeue, joining...
Producer Thread - 1 cannot find any file to enqueue, joining...
All threads have joined with main, exiting... Press any key to continue . . .
Sample Run 3
Please enter a file name: file1.txt
Please enter a file name: file2.txt
Please enter a file name: file3.txt
Please enter a file name: file4.txt
Please enter a file name: file5.txt
Please enter a file name: file6.txt
Please enter a file name: file7.txt
Please enter a file name: file8.txt
Please enter a file name: file9.txt
Please enter a file name: file10.txt
Please enter a file name: file11.txt
Please enter a file name: file12.txt
Please enter a file name: file13.txt
Please enter a file name: file14.txt
Please enter a file name: file15.txt
Please enter a file name: file16.txt
Please enter a file name: -
Producer Thread - 1 starts sleeping for 1727 milliseconds
Producer Thread - 2 starts sleeping for 1003 milliseconds
Consumer Thread - 1 starts sleeping for 2501 milliseconds
Consumer Thread - 2 starts sleeping for 2501 milliseconds
Consumer Thread - 3 starts sleeping for 2501 milliseconds
Producer Thread - 2 is now enqueuing "file16.txt"
Producer Thread - 2 starts sleeping for 2691 milliseconds
Producer Thread - 1 is now enqueuing "file15.txt"
Producer Thread - 1 starts sleeping for 2592 milliseconds
Consumer Thread - 1 is now handling "file16.txt"
Consumer Thread - 1 cannot process "file16.txt", there is no such file!
Consumer Thread - 2 is now handling "file15.txt" Consumer Thread - 1 starts sleeping for 3064 milliseconds Consumer Thread - 3 cannot find any file to dequeue for now.
Consumer Thread - 3 starts sleeping for 3064 milliseconds
Consumer Thread - 2 is done handling "file15.txt" with a shift of -- and written the result to "file15_decrypted.txt"
Consumer Thread - 2 starts sleeping for 3064 milliseconds
Producer Thread - 2 is now enqueuing "file14.txt"
Producer Thread - 2 starts sleeping for 1580 milliseconds
Producer Thread - 1 is now enqueuing "file13.txt"
Producer Thread - 1 starts sleeping for 2458 milliseconds
Producer Thread - 2 is now enqueuing "file12.txt"
Producer Thread - 2 starts sleeping for 3426 milliseconds
Consumer Thread - 1 is now handling "file14.txt"
Consumer Thread - 3 is now handling "file13.txt"
Consumer Thread - 1 is done handling "file14.txt" with a shift of -- and written the result to
"file14_decrypted.txt"
Consumer Thread - 3 is done handling "file13.txt" with a shift of -- and written the result to "file13_decrypted.txt"
Consumer Thread - 1 starts sleeping for 2693 milliseconds
Consumer Thread - 3 starts sleeping for 2693 milliseconds
Consumer Thread - 2 is now handling "file12.txt"
Consumer Thread - 2 is done handling "file12.txt" with a shift of -- and written the result to "file12_decrypted.txt"
Consumer Thread - 2 starts sleeping for 2693 milliseconds
Producer Thread - 1 is now enqueuing "file11.txt"
Producer Thread - 1 starts sleeping for 1161 milliseconds
Producer Thread - 1 is now enqueuing "file10.txt"
Producer Thread - 1 starts sleeping for 3601 milliseconds
Consumer Thread - 1 is now handling "file11.txt"
Consumer Thread - 3 is now handling "file10.txt"
Consumer Thread - 1 is done handling "file11.txt" with a shift of -- and written the result to "file11_decrypted.txt"
Consumer Thread - 1 starts sleeping for 3309 milliseconds
Consumer Thread - 3 is done handling "file10.txt" with a shift of -- and written the result to "file10_decrypted.txt"
Consumer Thread - 3 starts sleeping for 3309 milliseconds Consumer Thread - 2 cannot find any file to dequeue for now.
Consumer Thread - 2 starts sleeping for 3309 milliseconds
Producer Thread - 2 is now enqueuing "file9.txt"
Producer Thread - 2 starts sleeping for 2755 milliseconds
Producer Thread - 2 is now enqueuing "file8.txt"
Producer Thread - 2 starts sleeping for 2440 milliseconds
Producer Thread - 1 is now enqueuing "file7.txt"
Producer Thread - 1 starts sleeping for 3771 milliseconds
Consumer Thread - 1 is now handling "file9.txt"
Consumer Thread - 3 is now handling "file8.txt"
Consumer Thread - 2 is now handling "file7.txt"
Consumer Thread - 1 is done handling "file9.txt" with a shift of -- and written the result to
"file9_decrypted.txt"
Consumer Thread - 3 is done handling "file8.txt" with a shift of -- and written the result to
"file8_decrypted.txt"
Consumer Thread - 2 is done handling "file7.txt" with a shift of -- and written the result to
"file7_decrypted.txt"
Consumer Thread - 1 starts sleeping for 3085 milliseconds
Consumer Thread - 3 starts sleeping for 3085 milliseconds
Consumer Thread - 2 starts sleeping for 3085 milliseconds
Producer Thread - 2 is now enqueuing "file6.txt"
Producer Thread - 2 starts sleeping for 2051 milliseconds
Consumer Thread - 1 is now handling "file6.txt"
Consumer Thread - 3 cannot find any file to dequeue for now.
Consumer Thread - 3 starts sleeping for 2980 milliseconds Consumer Thread - 2 cannot find any file to dequeue for now.
Consumer Thread - 1 is done handling "file6.txt" with a shift of -- and written the result to
"file6_decrypted.txt"
Consumer Thread - 2 starts sleeping for 2980 milliseconds
Consumer Thread - 1 starts sleeping for 2980 milliseconds
Producer Thread - 1 is now enqueuing "file5.txt"
Producer Thread - 1 starts sleeping for 2881 milliseconds
Producer Thread - 2 is now enqueuing "file4.txt"
Producer Thread - 2 starts sleeping for 3688 milliseconds
Consumer Thread - 3 is now handling "file5.txt"
Consumer Thread - 3 is done handling "file5.txt" with a shift of -- and written the result to
"file5_decrypted.txt"
Consumer Thread - 2 is now handling "file4.txt"
Consumer Thread - 3 starts sleeping for 2850 milliseconds Consumer Thread - 1 cannot find any file to dequeue for now.
Consumer Thread - 1 starts sleeping for 2850 milliseconds
Consumer Thread - 2 is done handling "file4.txt" with a shift of -- and written the result to
"file4_decrypted.txt"
Consumer Thread - 2 starts sleeping for 2850 milliseconds
Producer Thread - 1 is now enqueuing "file3.txt"
Producer Thread - 1 starts sleeping for 1942 milliseconds
Producer Thread - 2 is now enqueuing "file2.txt"
Producer Thread - 2 starts sleeping for 3469 milliseconds
Producer Thread - 1 is now enqueuing "file1.txt"
Producer Thread - 1 starts sleeping for 1327 milliseconds
Consumer Thread - 3 is now handling "file3.txt"
Consumer Thread - 1 is now handling "file2.txt"
Consumer Thread - 3 is done handling "file3.txt" with a shift of 13 and written the result to
"file3_decrypted.txt"
Consumer Thread - 3 starts sleeping for 3396 milliseconds
Consumer Thread - 1 is done handling "file2.txt" with a shift of -- and written the result to
"file2_decrypted.txt"
Consumer Thread - 2 is now handling "file1.txt"
Consumer Thread - 1 starts sleeping for 3396 milliseconds
Consumer Thread - 2 is done handling "file1.txt" with a shift of -- and written the result to
"file1_decrypted.txt"
Consumer Thread - 2 starts sleeping for 3396 milliseconds
Producer Thread - 1 cannot find any file to enqueue, joining...
Producer Thread - 2 cannot find any file to enqueue, joining...
Consumer Thread - 3 cannot find any file to dequeue, joining...
Consumer Thread - 1 cannot find any file to dequeue, joining...
Consumer Thread - 2 cannot find any file to dequeue, joining...
All threads have joined with main, exiting... Press any key to continue . . .
Some Important Rules
Although some of the information is given below, please also read the assignment submission and grading policies from the lecture notes of the first week. In order to get a full credit, your program must be efficient, modular (with the use of functions), well commented and indented. Besides, you also have to use understandable identifier names. Presence of any redundant computation, bad indentation, meaningless identifiers, function names, or missing/irrelevant comments will decrease your grade in case that we detect them.
How to get help?
WE WILL NOT USE CODE RUNNER FOR THIS ASSIGNMENT!
Because of the multithreaded nature of the assignment, we will not use CodeRunner for this THE. 15 text files are given for you to test your implementation and you can create more files yourselves for testing, as well ( https://cryptii.com/caesar-cipher ). We will not use the same input files during grading. But you must still submit these text files along with your implementation.
Submit via SUCourse ONLY! Paper, e-mail or any other methods are not acceptable.
The internal clock of SUCourse might be a couple of minutes skewed, so make sure you do not leave the submission to the last minute. In the case of failing to submit your work on time: "No successful submission on SUCourse on time = A grade of 0 directly."
What and where to submit (PLEASE READ, IMPORTANT)
You should prepare your program using MS Visual Studio 2012, as we will use it while testing your submission this time.
It'd be a good idea to write your name and lastname in the program (as a comment line of course). Do not use any Turkish characters anywhere in your code (not even in comment parts). If your full name is "Duygu Karaoğlan Altop", and if you want to write it as comment; then you must type it as follows:
// Duygu Karaoglan Altop
Submission guidelines are below. Since the grading process will be semi-automatic, you are expected to strictly follow these guidelines. If you do not follow these guidelines, your grade will be zero. The lack of even one space character in the output will result in your grade being zero, so please test your programs yourself.
● Name the main.cpp into:
"SUCourseUserName_THE5.cpp"
Your SUCourse user name is actually your SUNet username which is used for checking sabanciuniv e-mails. Do NOT use any spaces, non-ASCII and Turkish characters in the file name. For example, if your SU e-mail address is duygukaltop@sabanciuniv.edu, then the file name must be: "duygukaltop_hw5.cpp".
● Please make sure that the files are the latest versions of your assignment program.
● You should upload the sample txt files, header and cpp files of the classes given to you (randgen and queue) and your main cpp file.
● Do not zip any of the documents but upload them as separate files only.
● Submit your work through SUCourse only!
Good Luck!
Ahmed Salem, Duygu K. Altop