Orders

Problem

Create a real-time system that emulates the fulfillment of delivery orders for a kitchen.

• The kitchen should receive 2 delivery orders per second.
• The kitchen should instantly cook the order upon receiving it
• Place the order on the best-availible shelf to await pick up by a courier

Receive the order, dispatch a courier to pick up and deliver that specific order
The courier should arrive randomly between 2-6 seconds later. The courier should instantly pick up the order upon arrival.The courier should instantly deliver it.

Orders

Orders must be parse from the file and ingested into your system 2 orders per second.

{
"id": "0ff534a7-a7c4-48ad-b6ec-7632e36af950",
"name": "Cheese Pizza",
"temp": "hot", // Preferred shelf storage temperature
"shelfLife": 300, // Shelf wait max duration (seconds)
"decayRate": 0.45 // Value deterioration modifier
}

Shelves

The kitchen pick-up area has multiple shelves to hold cooked at different temperatures.
Each order should be placed on a shelf that matches the order's temperature. If the shelf is full the an order can be placed on the overflow shelf.
If the overflow shelf is full, a random order should be discarded as waste from the overflow shelf.

Hot shelf :10
Cold shelf :10
Frozen shelf :10
Generic shelf :15

Shelf Life

Orders have an inherent value that will deteriorate over time, based on the order's shelfLife and decayRate fields. Orders that have reached a value of zero are considered wasted.
sh = shelfLife - orderAge - decayRate * orderAge * shelfDecayModifier / shelfLife.
shelfDecayModifier 1 for simple temp and 2 for the overflow shelf.

Calculate usage

The requests/ orders per second will be 2 per second so:
1 request per second = 2.5 million requests per month
2 request per second = 5 million requests per month

Analysis

As the problems consists in simulate a real time system delivering orders and the traffic will be heavy after I analyzed and
I decided to use a Event driven architecture so all the orders will be deliver asynchronously.

Architecture and Patterns

I decided to use an event based architecture because this architecture fits well the requirements. I am using the library called RX-JAVA to help me to implement this pattern using non-blocking asynchronous programming also using the observable pattern.

Concurrency Model

Functional programming is the process of building software by composing pure functions, avoiding shared state, mutable data, and side-effects
with this components we can avoid another problems when we are using blocking programming and share state in concurrency such data race or race contitions.
Also I decided to use it because although I am not an expert in concurrency I know that dealing with share state in concurrency is difficult when we need to scale and trace bugs.

The key part I analyzed to user rx-java was that it could help to get the following features out of the box:

• Responsive: The systems should respond in a timely manner.
• Message Driven: Systems should use async message-passing between components to ensure loose coupling.
• Elastic: Systems should stay responsive under high load.
• Resilient: Systems should stay responsive when some components fail.

Application Components:

The application consists in 4 components:
Kitchen --> Subject
Hot Shelf --> FlowableProcessor
Cold Shelf --> FlowableProcessor
Frozen Shelf --> FlowableProcessor
Generic Shelf --> FlowableProcessor

The subject and FlowableProcessor both are components provided by rx-java and both functionality is almost the same receive and send events the only difference is flowableProcessor can support BackPressure.
The flow is in that way: the Kitchen receive the initial orders from the json file, then the kitchen sends the orders by temperature to the especific shelf the shelf's size for each element is 10 and the generic's size is 15. When the shelf is full sends the order to the generic shelf and when the generic shelf is full discard the order from the generic shelf.

As each elements receive and emit orders there are 4 couriers.

Diagram

Technologies

• Java 8 and Maven
• Intellij Idea, Windows 10 Home
• RxJava 3
• Jackson and Log4j

Execute the project

The project is a maven project so in the root folder where the pom.xml execute:

mvn package

This will create the .jar but is a little bit slow because of the tests.

Execute the project with dependencies

If you want to create the jar with dependencies to execute from command-line, execute the next command:

mvn compile assembly:single

Go to the folder inside target , the file orders.json should be in the same folder, please copy it.

and in cmd or console execute the following command:

java -jar "Orders-1".jar 2 10 15

The first parameter is ELEMENTS_PER_SECOND
The second parameter is BUFFER_SIZE_SHELF
The third parameter is ELEMENTS_PER_SECOND

These variables already are defined by default with the same value, so you can change it if you want.