Lab 0: Ping Server Overview

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Questions and Answers

What does the PingClient do when it receives a Ping command?

It sends a PingRequest and sets a PingTimer. (correct)

It waits for a signal before sending the command.

It sends a PongReply to the server immediately.

It ignores the command and waits for a Pong reply.

Under what condition does the PingClient re-send a PingRequest?

When a PongReply is received with an incorrect value.

When the PingTimer elapses and Pong has not been received. (correct)

When the server is busy with another request.

When the PingClient is initialized.

What does the hasResult() method in PingClient indicate?

Whether the next PingRequest has been sent.

If a Pong reply has been stored. (correct)

Whether the PingClient is ready for a new command.

If the PingTimer has expired.

What exception is thrown if the PingClient receives a command that is not a Ping?

IllegalArgumentException Signup and view all the answers

What role does the PingRequest class serve in the communication process?

It encapsulates the data for the Ping to be sent. Signup and view all the answers

What does the PingTimer class facilitate in the PingClient?

It determines the maximum wait time for a Pong reply. Signup and view all the answers

What is a critical function of the handlePongReply() method in PingClient?

To check if the Pong reply matches the sent Ping value. Signup and view all the answers

What is the purpose of implementing the Client interface in PingClient?

To enforce a correct implementation of client-specific methods. Signup and view all the answers

What is the primary function of the PingApplication class?

To respond to Ping commands with corresponding Pong results. Signup and view all the answers

What type of object does the PingApplication expect as its command in the execute method?

Ping Signup and view all the answers

What role does the PingServer play in the distributed system?

It is the basic unit of computation that manages the PingApplication. Signup and view all the answers

What exception is thrown if an invalid command is passed to the PingApplication's execute method?

IllegalArgumentException Signup and view all the answers

Which class is responsible for handling PingRequest messages in the PingServer?

handlePingRequest Signup and view all the answers

What does the Pong class represent within the PingApplication framework?

The response sent back to a Ping command. Signup and view all the answers

What happens when a PingRequest is received by the PingServer?

The Ping command is passed to the PingApplication for a result. Signup and view all the answers

What does the PingServer's init method indicate?

No initialization is necessary for the server. Signup and view all the answers

Study Notes

Overview of Distributed System

Involves a Ping Server that responds to Ping requests from clients.
Clients send Ping commands, which the server processes and returns Pong results.

PingApplication Class

Acts as a simple state machine consisting of Commands and Results.
Contains the Ping command class that includes a non-null string value.
Contains the Pong result class that returns the same string value as the Ping.
Executes by checking if the command instance is Ping; otherwise, it throws an IllegalArgumentException.
Returns a Pong object containing the same value from the received Ping.

PingServer Class

Inherits from Node, comprising the main computing unit of a distributed system.
Initializes a PingApplication instance and has a message handler for Ping requests.
The handler processes PingRequest messages, invokes the PingApplication’s execute method, and sends back a PongReply.

Message Classes

PingRequest: Encapsulates a Ping command for sending to the server.
PongReply: Encapsulates a Pong result for sending back to the client.

PingClient Class

Inherits from Node and implements the Client interface.
Holds a reference to the server address for communication.
Manages Ping and Pong states with synchronized methods for thread safety.
On sending a Ping command, it issues a PingRequest to the server and sets a PingTimer.
Implements hasResult() to check if a Pong has been received and getResult() to return the Pong.
Handles received Pong replies through handlePongReply, notifying when the response matches the original Ping value.
Resends requests if Pong is not received before the PingTimer expires, ensuring reliable communication.

PingTimer Class

Contains a constant RETRY_MILLIS, set at 10 milliseconds for retrying Ping requests.
Triggers re-delivery of the Ping to the server if no response is received within the timer period.

Important Concepts

The structure encourages separation of commands and results for clarity and scalability.
Resilience is integrated via the PingClient which persistently retries until a Pong response is acquired.
Clear communication protocols defined by message classes facilitate interaction between client and server.

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Description

This lab introduces the Ping Server application and its role in a simple distributed system. Participants will explore how clients ping the server and understand the basic interface and testing infrastructure involved. Gain insights into state machines and how they interact within this framework.