concpar22final02.md



Problem 2: Wait and Notify

Setup
Use the following commands to make a fresh clone of your repository:

git clone -b concpar22final02 git@gitlab.epfl.ch:lamp/student-repositories-s22/cs206-GASPAR.git concpar22final02


If you have issues with the IDE, try reimporting the
build,
if you still have problems, use compile in sbt instead.

Problem 2.1: Implement Barrier methods
Your first task is to implement a barrier. A barrier acts as a synchronization point between multiple threads. It is used when you want all threads to finish a task before starting the next one.
You have to complete the following two methods in the Barrier class:


awaitZero function waits for the count value to be zero.

countDown function decrements the count by one. It notifies other threads if count is less than or equal to zero.

The barrier will be implemented using these functions. When the thread finish a task, it will decrement the count by using the countDown function. Then, it will call the awaitZero function to wait for other threads.

Problem 2.2: Use the Barrier to apply filters to an image
In this part, each thread will apply an array of filters to each row of the image. Your task is to use the Barrier to act as a synchronization point while applying the filters. Each thread should wait for the other threads to complete the current filter before applying the next filter.
ImageLib.scala provides an implementation of an image processing library with different filters. Each filter has a kernel which is applied on the image. ImageLib.scala implements four different filters. It provides an applyFilter method which applies a particular filter's kernel on a particular row on the input Array and generates the output in the output Array.
The ImageLib class takes the size of an image as input. The image is a square matrix. The class has two buffers buffer1 and buffer2. The initial image will be in buffer1. For the filtering task, you will switch between these buffers as input and output. For example, for the first filter buffer1 will the input buffer and buffer2 will be the output buffer. For the second filter buffer2 will the input and buffer1 will be the output and so on for subsequent filters.
In Problem2.scala file where you will complete the imagePipeline function:

The imagePipeline function gets a array of filters and an array of row numbers. This filter needs to be applied to all the rows present in row array. After applying each filter, the thread has to wait for other threads to complete before applying the next filter. You will use barrier in this case.
The imagePipeline function will return the output buffer. Note the output buffer can change between buffer1 and buffer2 depending on the number of filters applied.

You can get partial points for solving parts of this exercise.