CSE-5306-001 Distributed Systems Project 1 Name – Ranjith Gopal Reddy Student id – 1002028255

Introduction, This project is about the client-server architecture to handle file operations like UPLOAD, DELETE, DOWNLOAD, RENAME and 2 other operations which is ADD and SORT operations. The mentioned operations are implemented using Java RMI system. RMI provides for remote communication between programs written in the Java programming language between server and client.

Part 1 - To implement multi-threaded file server that supports UPLOAD, DOWNLOAD, DELETE, and RENAME file operations. Here we have 2 files server.java and client.java. As the name suggests server, this acts as a remote object and handles remote procedure calls requested by the client. On the client side we have a stub object which has the connection details to the server and stub is responsible for all the requests performed to the server. In this part, the server handles UPLOAD, DELETE, RENAME, DELETE file operations based on the client request. To handle these operations smoothly, create 2 directories one for client side files and one for server side files, Client directory - C:\CSE5306\Client Files Server directory - C:\CSE5306\Server Files Now let us look at how to perform these activities, Steps:

1. Open CLI is source code directory
2. Compile and run server java code, javac server.java java server.java
3. Compile and run client java code, javac .\ClientFactory.java javac .\Client.java
4. To upload file, java .\Client.java upload .
5. To download file from server, java .\Client.java download . Optionally to see, what files are available on server for download, you can run java java .\Client.java listfiles
6. To rename file on server, java .\Client.java rename <old_filename>. <new_filename>.
7. To delete file on server, java .\Client.java delete . Learnings, Introduction to RMI and understanding of client-server architecture and implementation of this architecture. Challenges faced, • When setting up the server system, when tried to restart the server. Second time execution of server failed because there was no dedicated porty assigned initially. • At first we have had dependency on rmiregistry, which we had to run on separate CLI and execute the server. We introduced createRegistry in code to fix this dependency.

Part-2 - To make the file operations transparent between client and server, we have created a helper thread which always executes and finds if there is any new file created, modified and deleted on the client side and automatically makes these changes on the server. For this we have made use of Java WatchService API, which always monitors a particular directory and notifies for changes in the directory. Based on this thread we invoke respective file operation functions Steps:

1. Compile and run helper thread javac .\Helper.java java .\Helper.java
2. Now go to the client files directory and create or delete or modify a file. And you can notice that these changes are reflected on the server. Learnings, Introduction to WatchService APi and understanding of how a service can monitor the directory and can invoke respective functions.

Part-3 - Implement add(I,j) and sort(array A), and demonstrate synchronous and asynchronous RPC calls. Add and sort functions are implemented as a part of server code, and we can invoke the add and subtract command from the client program. For example,

1. java .\Client.java adder 2 3 5

2. java .\Client.java sorter 2,1,3,4 [2, 1, 3, 4] [1, 2, 3, 4] As this part speaks about synchronous and asynchronous communication, we have created 2 programs SynchronousClient.java and AsynchronousClient.java where we can run these files without any arguments to be passed, as we hard coded the inputs as (2,3) for addition and {5, -2, 23, 7, 87, -42, 509} for the array to be sorted. For both the functions there is a 10 secs delay introduced to demonstrate the working mechanism. For both the programs we have timestamps recorded, to have a clear idea about the execution.

3. SynchronousClient execution timestamps on Client side are below, As we notice above that 10 secs after addition is executed, sorting function starts. Now let us look at Server side timestamps, We can notice the same here as well. One important thing to note is, both the functions happened to run on the same thread. main thread on client side thread 16 on server side

4. AsynchronousClient execution timestamps on Client side are below, As we notice above, even though there is 10 secs delay introduced, both the function executions happened to be in parallel as both the calls were asynchronous in nature. Server-side timestamps, On the Server side also the executions are asynchronous, which happened to start at 10:47:51 precisely. Again, if we look at the threads, Client side - Pool-worker-1 for add function Pool-worker-2 for sort function Server side - Thread 22 for add function Thread 21 for sort function Asynchronous mechanism is implemented using inbuilt Java CompletableFuture class. Learnings, Introduction to CompletableFuture class which speaks about the asynchronous mechanism implementation in Java. Along side also had an understanding of how Java evolved to implement asynchronous mechanism more productively. Right from Threads, Runnable, Callable, Futures to more evolved version CompletableFuture. References - WatchService API - WatchService (Java Platform SE 7 ) (oracle.com) RMI system - Trail: RMI (The Java™ Tutorials) (oracle.com) Completable Future(Asynchronous mechanism) - CompletableFuture (Java Platform SE 8 ) (oracle.com)