Lab #5: Threads (DRAFT) Solution

Concurrency and Locks




In Lab 5, you will convert a single-threaded application into a multithreaded one. The libraries you will be introduced to are ncurses and pthreads. You will not be required to actually code any ncurses APIs.




Learning Objectives




Install the ncurses library and documentation



Modify a small program to use threads and the resulting program "thread-safe"



Assignment




Begin by installing the tools you will need for this assignment:




mkdir -p ~/cs3100/lab5




cd ~/cs3100/lab5




sudo apt-get update




sudo apt-get install ncurses-dev ncurses-doc




scp USER@icarus.cs.weber.edu:/var/classes/cs3100/lab5/lab5.tar . tar xvf lab5.tar




The file lab5.tar file will create, when extracted, a folder called template which will contain these files:




window.c




Makefile




You are to modify window.c and enable it to be a multi-threaded application. Window.c creates two tiled windows with a horizontal line between them, and continuously writes to both screens simultaneously until the user hit a key on the keyboard. You will create a separate thread for each of the two windows but keep in mind that ncurses is NOT thread-safe, meaning it is not reentrant. You are required to use a mutex to prevent multiple simultaneous calls to any ncurses function. To find out which functions are ncurses, use the man command for every function called in the program. As delivered, window.c just creates the two windows and the horizontal bar, then exits. It is your job to get it to display the counts.




What you must do to window.c to make it multi-threaded:




Make these changes to window.c:




Locate the code in window.c that initializes ncurses, creates the top and bottom windows and initialize color support. Just after the color support, create a mutex for controlling access to ncurses. Name your mutex variable "ncurses".



Locate for two functions called countUp() and countDown() that prints to the appropriate window and performs the counting. These two functions should be identical except for the direction they count and the window they use for output. In countUp() and countDown() you should surround all of the calls to any ncurses function with your mutex, creating a critical section.



Page !1 of !3
Just after the comment "// Thread code goes here!", create two threads with the pthreads API, one for each window, calling countUp() and countDown() as appropriate. There are examples in the text and also in Advanced Programming in the Unix Environment. Of course, you may also research this on the Internet.
Also add code to wait for each of the two threads to terminate.



Compile and test. If one of your windows seems to lock up, look to see if you are forgetting to unlock the mutex. If the horizontal line disappears and it seems as if the threads are writing into the wrong window, look to see if you properly protected all of the ncurses function calls.



Sample Output










Your output should look something like this. The top window should always be green on black, the bottom red on black. There is a blue line between the two windows. There should never be any window corruption, the blue line should never disappear or change and it should take TWO keystrokes to end the program. We will discuss why in class.







Let your program run for a minute or so to ensure your solution is completely thread-safe. You will know almost immediately if it is not.



















Files




Here is a list of the files created or modified in this lab.




window.c




Please add your name, lab # (5) and class # (CS 3100) as comments at the top of window.c.








Additional Requirements




Please modify this program as simply as possible. Do not add any prompts, output or any file I/O except as specified for each program. Do not remove or rearrange any code from window.c.



Do not modify countUp() or countDown() except to add the critical sections as required, along with any local variables you may need.



Do not modify main() except for the thread creation and synchronization code and any local or global variables you may need.
Upload only window.c to Canvas for grading as you turn in this assignment.



Page !2 of !3
Grading




This assignment is a bit too complex for cucumber grading. I will compile and run your window.c, review your source code and give you points based on my observation.




Upload your window.c file for this assignment to Canvas when you are ready for me to grade your work.
It is not necessary to upload any files to icarus for this assignment.



As always, you are free to deviate from the requirements for this assignment and you agree that if you do, you will receive a zero for the assignment.



Here is how you earn points for this assignment:




FEATURES
POINTS




Must-Have Features






Only the following file is uploaded to Canvas:
10
window.c


window.c compiles without errors or warnings
10
window implements pthread APIs to create two threads, one executing


countUP(), the other countDown() and waits for both threads to complete.


window correctly creates two equally sized windows and immediately begins
10
counting up in the top window in green and counting down in the bottom window,


with a dashed line between the two windows






window causes one of the two windows to stop counting on a single keystroke
10
window causes the other window to stop counting on the second keystroke and
10
terminates the program after a three second pause.






window runs without creating any screen artifacts, corrupting or removing the
50
dashed line during execution or crashing during or at the end of execution










Grand Total
100

















































Page !3 of !3