Problem 1. Matrix multiplication (50 points)
In this exercise we will continue to work on the matrix ADT.
An implementation of matrix ADT (abstract data type) is given in matrix.c. The API (application programming interface) functions that operates on the matrices are listed in matrix.h. One of the functions,
mulMatrix(), performs matrix multiplication, which is implemented in matrix.c.
In this assignment, we implement mulMatrix thread() in mmul.c, which has the same interface as mulMatrix(),
but performs matrix multiplication with two threads. We only need to change mmul.c.
test-mmul.c is provided to test our implementation. The program takes the following arguments from the
command line: the number of rows in the first matrix, the number of columns in the first matrix, and the
number of columns in the second matrix. Then it fills two matrices with random numbers, and compares
the result of mulMatrix() and mulMatrix thread(). If no argument is specified, the program works on two
matrices of size 6 Ã— 6. In addition, if a command line option -t<n> is present, test-mmul prints the time (in
seconds) spent on matrix multiplications, using the average of <n> calls.
Here are some sample sessions running test-mmul. The first command multiplies a matrix of 1000 by 500
with a matrix of 500 by 800. The resulting matrix is 1000 by 800. The second command also shows the
timing information, the average of calling each multiplication function 3 times. time1 is the average time
on mulMatrix() and time2 is the average time on mulMatrix thread(). The numbers are likely to change
in different runs.
$./test-mmul 1000 500 800
$./test-mmul 100 500 300 -t3
num_runs=3 time1=0.0652 time2=0.0341 speedup=1.9132
Problem 2. Printing (50 points)
Suppose p printers need to get j print jobs done. The print jobs are already placed in a queue. The starter
code printing.c defines a type job_queue_t for the queue and provides functions to operate on the queue.
A printer performs the following operations in a loop.
the job takes
amounts of time to complete.
The function printer_single() in the starter code printing.c shows how a single printer completes all
The tasks in this problem are to use threads to simulate the process of multiple printers completing the print
jobs. Each thread is a printer and performs similar operations as printer_single(). Apparently, threads
need to coordinate their operations on the queue, which is shared by all printers. A mutex is defined in the
job_queue_t structure for this purpose.
The program printing takes optional arguments from the command line. An argument can be one of the
â€¢ -p <n>. Specify the number of printers. The default value is 2.
â€¢ -j <n>. Specify the number of jobs. The default value is 20.
â€¢ -d. Call the demo function showing the operations of a single printer and exit.
Checking results. A script check-printing.py is provided to check the output of printing. Below is an
example of how to use check-printing.py.
$./printing -p 5 -j 1000 | python3 ./check-printing.py
If you have made check-printing.py executable by command "chmod +x ./check-printing.py", you can
run it directly.
$./printing -p 5 -j 1000 | ./check-printing.py
Note that it is not guaranteed that a program that passes the check is correct. We should also examine the
output manually sometimes. Some synchronization errors may manifest themselves only for some values of
the parameters. And even for the same parameters, errors may happen non-deterministically due to different
timing and scheduling orders of the threads. You may run the program multiple times even with the same
parameters. For example, the following bash command runs the above example for 10 times. (Yes, it looks
like a loop in C! and it may not work in other shells.)
for ((n=0;n<10;n++)); do ./printing -p 5 -j 1000 | python3 check-printing.py; done
Debugging. gdb supports multithreading. Run your code in gdb until it stops at a breakpoint or appears
to stop making progress. If threads are not making progress, interrupt the execution with Ctrl-C to get to
the gdb prompt. Here are some commonly used thread commands.
â€¢ info threads See what threads are running.
â€¢ thread n Switch to thread n, where n is a thread number.
â€¢ thread apply [threadno] [all] args Apply commands to one or more threads.
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