Welcome!

Java IoT Authors: Ed Featherston, Elizabeth White, Liz McMillan, Yeshim Deniz, Pat Romanski

Related Topics: Java IoT

Java IoT: Article

Next-Gen Concurrency in Java: The Actor Model

Multiple concurrent processes can communicate with each other without needing to use shared state variables

At a time where the clock speeds of processors have been stable over the past couple of years, and Moore's Law is instead being applied by increasing the number of processor cores, it is getting more important for applications to use concurrent processing to reduce run/response times, as the time slicing routine via increased clock speed will no longer be available to bail out slow running programs.

Carl Hewitt proposed the Actor Model in 1973 as a way to implement unbounded nondeterminism in concurrent processing. In many ways this model was influenced by the packet switching mechanism, for example, no synchronous handshake between sender and receiver, inherently concurrent message passing, messages may not arrive in the order they were sent, addresses are stored in messages, etc.

The main difference between this model and most other parallel processing systems is that it uses message passing instead of shared variables for communication between concurrent processes. Using shared memory to communicate between concurrent processes requires the application of some form of locking mechanism to coordinate between threads, which may give rise to live locks, deadlocks, race conditions and starvation.

Actors are the location transparent primitives that form the basis of the actor model. Each actor is associated with a mailbox (which is a queue with multiple producers and a single consumer) where it receives and buffers messages, and a behavior that is executed as a reaction to a message received. The messages are immutable and may be passed between actors synchronously or asynchronously depending on the type of operation being invoked. In response to a message that it receives, an actor can make local decisions, create more actors, send more messages, and designate how to respond to the next message received. Actors never share state and thus don't need to compete for locks for access to shared data.

The actor model first rose to fame in the language Erlang, designed by Ericcson in 1986. It has since been implemented in many next-generation languages on the JVM such as Scala, Groovy and Fantom. It is the simplicity of usage provided via a higher level of abstraction that makes the actor model easier to implement and reason about.

It's now possible to implement the actor model in Java, thanks to the growing number of third-party concurrency libraries advertising this feature. Akka is one such library, written in Scala, that uses the Actor model to simplify writing fault-tolerant, highly scalable applications in both Java and Scala.

Implementation
Using Akka, we shall attempt to create a concurrent processing system for loan request processing in a bank as can be seen in the Figure 1.

Figure 1

The system consists of four actors:

  1. The front desk - which shall receive loan requests from the customers and send them to the back office for processing. It shall also maintain the statistics of the number of loans accepted/rejected and print a report detailing the same on being asked to do so.
  2. The back office - which shall sort the loan requests into personal loans and home loans, and send them to the corresponding accountant for approval/rejection.
  3. The personal loan accountant - who shall process personal loan requests, including approving/rejecting the requests, carrying out credit history checks and calculating the rate of interest.
  4. The home loan accountant - who shall process home loan requests, including approving/rejecting the requests, carrying out credit history checks and calculating the rate of interest.

To get started, download the version 2.0 of Akka for Java from http://akka.io/downloads and add the jars present in ‘akka-2.0-RC4\lib' to the classpath.

Next, create a new Java class "Bank.java" and add the following import statements :

import akka.actor.ActorRef;

import akka.actor.ActorSystem;

import akka.actor.Props;

import akka.actor.UntypedActor;

import akka.routing.RoundRobinRouter;

Now, create a few static nested classes under ‘Bank' that will act as messages (DTOs) and be passed to actors.

1. ‘LoanRequest' will contain the following elements and their corresponding getters/setters:

int requestedLoan;
int
accountBalance;

2. ‘PersonalLoanRequest' will extend ‘LoanRequest' and contain the following element and its corresponding getter:

final static String type="Personal";

3. ‘HomeLoanRequest' will extend ‘LoanRequest' and contain the following element and its corresponding getter:

final static String type="Home";

4. ‘LoanReply' will contain the following elements and their corresponding getters/setters:

String type;
boolean
approved;
int
rate;

Next, create a static nested class ‘PersonalLoanAccountant' under ‘Bank'.

public static class PersonalLoanAccountant extends UntypedActor {
public
int rateCaluclation(int requestedLoan, int accountBalance) {
if
(accountBalance/requestedLoan>=2)
return
5;
else

return
6;
}

public
void checkCreditHistory() {
for
(int i=0; i<1000; i++) {
continue
;
}
}
public
void onReceive(Object message) {
if
(message instanceof PersonalLoanRequest) {
PersonalLoanRequest request=PersonalLoanRequest.class.cast(message);
LoanReply reply = new LoanReply();
reply.setType(request.getType());
if
(request.getRequestedLoan()<request.getaccountBalance()) {
reply.setApproved(true);
reply.setRate(rateCaluclation(request.getRequestedLoan(), request.getaccountBalance()));
checkCreditHistory();
}
getSender().tell(reply);
} else {
unhandled(message);
}
}
}

The above class  serves as an actor in the system. It extends the ‘UntypedActor' base class provided by Akka and must define its ‘onReceive‘ method. This method acts as the mailbox and receives messages from other actors (or non-actors) in the system. If the message received is of type 'PersonalLoanRequest', then it can be processed by approving/rejecting the loan request, setting the rate of interest and checking the requestor's credit history. Once the processing is complete, the requestor uses the sender's reference (which is embedded in the message) to send the reply (LoanReply) to the requestor via the ‘getSender().tell()' method.

Now, create a similar static nested class ‘HomeLoanAccountant' under ‘Bank'

public static class HomeLoanAccountant extends UntypedActor {
public
int rateCaluclation(int requestedLoan, int accountBalance) {
if
(accountBalance/requestedLoan>=2)
return
7;
else

return
8;
}

public
void checkCreditHistory() {
for
(int i=0; i<2000; i++) {
continue
;
}
}
public
void onReceive(Object message) {
if
(message instanceof HomeLoanRequest) {
HomeLoanRequest request=HomeLoanRequest.class.cast(message);
LoanReply reply = new LoanReply();
reply.setType(request.getType());
if
(request.getRequestedLoan()<request.getaccountBalance()) {
reply.setApproved(true);
reply.setRate(rateCaluclation(request.getRequestedLoan(), request.getaccountBalance()));
checkCreditHistory();
}
getSender().tell(reply);
} else {
unhandled(message);
}
}
}

Now, create a static nested class ‘BackOffice' under ‘Bank':

public static class BackOffice extends UntypedActor {

ActorRef personalLoanAccountant=getContext().actorOf(new Props(PersonalLoanAccountant.class).withRouter(new RoundRobinRouter(2)));
ActorRef homeLoanAccountant=getContext().actorOf(new Props(HomeLoanAccountant.class).withRouter(new RoundRobinRouter(2)));

public void onReceive(Object message) {
if
(message instanceof PersonalLoanRequest) {
personalLoanAccountant.forward(message, getContext());
} else if (message instanceof HomeLoanRequest) {
homeLoanAccountant.forward(message, getContext());
} else {
unhandled(message);
}
}

}

The above class serves as an actor in the system and is purely used to route the incoming messages to PersonalLoanAccountant or HomeLoanAccountant, based on the type of message received. It defines actor references ‘personalLoanAccountant' and ‘homeLoanAccountant' to ‘PersonalLoanAccountant.class' and ‘HomeLoanAccountant.class', respectively. Each of these references initiates two instances of the actor it refers to and attaches a round-robin router to cycle through the actor instances. The ‘onReceive' method checks the type of the message received and forwards the message to either ‘PersonalLoanAccountant' or ‘HomeLoanAccountant' based on the message type. The ‘forward()' method helps ensure that the reference of the original sender is maintained in the message, so the receiver of the message (‘PersonalLoanAccountant' or ‘HomeLoanAccountant') can directly reply back to the message's original sender.

Now, create a static nested class ‘FrontDesk' under ‘Bank':

public static class FrontDesk extends UntypedActor {
int
approvedPersonalLoans=0;
int
approvedHomeLoans=0;
int
rejectedPersonalLoans=0;
int
rejectedHomeLoans=0;

ActorRef backOffice=getContext().actorOf(
new Props(BackOffice.class), "backOffice");

public
void maintainLoanApprovalStats(Object message) {
LoanReply reply = LoanReply.class.cast(message);
if
(reply.isApproved()) {
System.out.println(reply.getType()+" Loan Approved"+" at "+reply.getRate()+"% interest.");
if
(reply.getType().equals("Personal"))
++approvedPersonalLoans;
else
if(reply.getType().equals("Home"))
++approvedHomeLoans;
} else {
System.out.println(reply.getType()+" Loan Rejected");
if
(reply.getType().equals("Personal"))
++rejectedPersonalLoans;
else
if(reply.getType().equals("Home"))
++rejectedHomeLoans;
}
}

public void printLoanApprovalStats() {
System.out.println("--- REPORT ---");
System.out.println("Personal Loans Approved : "+approvedPersonalLoans);
System.out.println("Home Loans Approved : "+approvedHomeLoans);
System.out.println("Personal Loans Rejected : "+rejectedPersonalLoans);
System.out.println("Home Loans Rejected : "+rejectedHomeLoans);
}
public
void onReceive(Object message) {
if
(message instanceof LoanRequest) {
backOffice.tell(message, getSelf());
} else if (message instanceof LoanReply) {
maintainLoanApprovalStats(message);
} else if(message instanceof String && message.equals("printLoanApprovalStats")) {
printLoanApprovalStats();
getContext().stop(getSelf());
} else {
unhandled(message);
}
}
}

The above class serves as the final actor in the system. It creates a reference ‘backOffice' to the actor ‘BackOffice.class'. If the message received is of type ‘LoanRequest', it sends the message to ‘BackOffice' via the method ‘backOffice.tell()', which takes a message and the reference to the sender (acquired through the method ‘getSelf()') as arguments. If the message received is of type ‘LoanReply', it updates the counters to maintain the approved/rejected counts. If the message received is "printLoanApprovalStats", it prints the stats stored in the counters, and then proceeds to stop itself via the method ‘getContext().stop(getSelf())'. The actors follow a pattern of supervisor hierarchy, and thus this command trickles down the hierarchy chain and stops all four actors in the system.

Finally, write a few methods under ‘Bank' to submit requests to the ‘FrontOffice':

public static void main(String[] args) throws InterruptedException {
ActorSystem system = ActorSystem.create("bankSystem");
ActorRef frontDesk = system.actorOf(new Props(FrontDesk.class), "frontDesk");
submitLoanRequests
(frontDesk);
Thread.sleep(1000);
printLoanApprovalStats
(frontDesk);
system.shutdown();
}

public
static PersonalLoanRequest getPersonalLoanRequest() {
int
min=10000; int max=50000;
int
amount=min + (int)(Math.random() * ((max - min) + 1));
int
balance=min + (int)(Math.random() * ((max - min) + 1));
return
(new Bank()).new PersonalLoanRequest(amount, balance);
}

public
static HomeLoanRequest getHomeLoanRequest() {
int
min=50000; int max=90000;
int
amount=min + (int)(Math.random() * ((max - min) + 1));
int
balance=min + (int)(Math.random() * ((max - min) + 1));
return
(new Bank()).new HomeLoanRequest(amount, balance);
}

public static void submitLoanRequests(ActorRef frontDesk) {
for
(int i=0;i<1000;i++) {
frontDesk.tell(getPersonalLoanRequest());
frontDesk.tell(getHomeLoanRequest());
}
}

public static void printLoanApprovalStats(ActorRef frontDesk) {
frontDesk.tell("printLoanApprovalStats");
}

The method ‘main' creates an actor system ‘system' using the method ‘ActorSystem.create()'. It then creates a reference ‘frontDesk' to the actor ‘FrontDesk.class'. It uses this reference to send a 1000 requests each of types ‘PersonalLoanRequest' and ‘HomeLoanRequest' to ‘FrontDesk'. It then sleeps for a second, following which it sends the message "printLoanApprovalStats" to ‘FrontDesk'. Once done, it shuts down the actor system via the method ‘system.shutdown()'.

Conclusion
Running the above code will create a loan request processing system with concurrent processing capabilities, and all this without using a single synchronize/lock pattern. Moreover, the code doesn't need one to go into the low-level semantics of the JVM threading mechanism or use the complex ‘java.util.concurrent' package. This mechanism of concurrent processing using the Actor Model is truly more robust as multiple concurrent processes can communicate with each other without needing to use shared state variables.

More Stories By Sanat Vij

Sanat Vij is a professional software engineer currently working at CenturyLink. He has vast experience in developing high availability applications, configuring application servers, JVM profiling and memory management. He specializes in performance tuning of applications, reducing response times, and increasing stability.

Comments (0)

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


@ThingsExpo Stories
One of biggest questions about Big Data is “How do we harness all that information for business use quickly and effectively?” Geographic Information Systems (GIS) or spatial technology is about more than making maps, but adding critical context and meaning to data of all types, coming from all different channels – even sensors. In his session at @ThingsExpo, William (Bill) Meehan, director of utility solutions for Esri, will take a closer look at the current state of spatial technology and ar...
According to Forrester Research, every business will become either a digital predator or digital prey by 2020. To avoid demise, organizations must rapidly create new sources of value in their end-to-end customer experiences. True digital predators also must break down information and process silos and extend digital transformation initiatives to empower employees with the digital resources needed to win, serve, and retain customers.
A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, wh...
Complete Internet of Things (IoT) embedded device security is not just about the device but involves the entire product’s identity, data and control integrity, and services traversing the cloud. A device can no longer be looked at as an island; it is a part of a system. In fact, given the cross-domain interactions enabled by IoT it could be a part of many systems. Also, depending on where the device is deployed, for example, in the office building versus a factory floor or oil field, security ha...
Businesses are struggling to manage the information flow and interactions between all of these new devices and things jumping on their network, and the apps and IT systems they control. The data businesses gather is only helpful if they can do something with it. In his session at @ThingsExpo, Chris Witeck, Principal Technology Strategist at Citrix, will discuss how different the impact of IoT will be for large businesses, expanding how IoT will allow large organizations to make their legacy ap...
19th Cloud Expo, taking place November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy. Meanwhile, 94% of enterpri...
Ask someone to architect an Internet of Things (IoT) solution and you are guaranteed to see a reference to the cloud. This would lead you to believe that IoT requires the cloud to exist. However, there are many IoT use cases where the cloud is not feasible or desirable. In his session at @ThingsExpo, Dave McCarthy, Director of Products at Bsquare Corporation, will discuss the strategies that exist to extend intelligence directly to IoT devices and sensors, freeing them from the constraints of ...
In this strange new world where more and more power is drawn from business technology, companies are effectively straddling two paths on the road to innovation and transformation into digital enterprises. The first path is the heritage trail – with “legacy” technology forming the background. Here, extant technologies are transformed by core IT teams to provide more API-driven approaches. Legacy systems can restrict companies that are transitioning into digital enterprises. To truly become a lea...
24Notion is full-service global creative digital marketing, technology and lifestyle agency that combines strategic ideas with customized tactical execution. With a broad understand of the art of traditional marketing, new media, communications and social influence, 24Notion uniquely understands how to connect your brand strategy with the right consumer. 24Notion ranked #12 on Corporate Social Responsibility - Book of List.
Why do your mobile transformations need to happen today? Mobile is the strategy that enterprise transformation centers on to drive customer engagement. In his general session at @ThingsExpo, Roger Woods, Director, Mobile Product & Strategy – Adobe Marketing Cloud, covered key IoT and mobile trends that are forcing mobile transformation, key components of a solid mobile strategy and explored how brands are effectively driving mobile change throughout the enterprise.
SYS-CON Events announced today that CDS Global Cloud, an Infrastructure as a Service provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. CDS Global Cloud is an IaaS (Infrastructure as a Service) provider specializing in solutions for e-commerce, internet gaming, online education and other internet applications. With a growing number of data centers and network points around the world, ...
SYS-CON Events announced today that LeaseWeb USA, a cloud Infrastructure-as-a-Service (IaaS) provider, will exhibit at the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. LeaseWeb is one of the world's largest hosting brands. The company helps customers define, develop and deploy IT infrastructure tailored to their exact business needs, by combining various kinds cloud solutions.
Technology vendors and analysts are eager to paint a rosy picture of how wonderful IoT is and why your deployment will be great with the use of their products and services. While it is easy to showcase successful IoT solutions, identifying IoT systems that missed the mark or failed can often provide more in the way of key lessons learned. In his session at @ThingsExpo, Peter Vanderminden, Principal Industry Analyst for IoT & Digital Supply Chain to Flatiron Strategies, will focus on how IoT de...
WebRTC is bringing significant change to the communications landscape that will bridge the worlds of web and telephony, making the Internet the new standard for communications. Cloud9 took the road less traveled and used WebRTC to create a downloadable enterprise-grade communications platform that is changing the communication dynamic in the financial sector. In his session at @ThingsExpo, Leo Papadopoulos, CTO of Cloud9, discussed the importance of WebRTC and how it enables companies to focus...
There is little doubt that Big Data solutions will have an increasing role in the Enterprise IT mainstream over time. Big Data at Cloud Expo - to be held November 1-3, 2016, at the Santa Clara Convention Center in Santa Clara, CA - has announced its Call for Papers is open. Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is...
The Internet of Things can drive efficiency for airlines and airports. In their session at @ThingsExpo, Shyam Varan Nath, Principal Architect with GE, and Sudip Majumder, senior director of development at Oracle, will discuss the technical details of the connected airline baggage and related social media solutions. These IoT applications will enhance travelers' journey experience and drive efficiency for the airlines and the airports. The session will include a working demo and a technical d...
Big Data has been changing the world. IoT fuels the further transformation recently. How are Big Data and IoT related? In his session at @BigDataExpo, Tony Shan, a renowned visionary and thought leader, will explore the interplay of Big Data and IoT. He will anatomize Big Data and IoT separately in terms of what, which, why, where, when, who, how and how much. He will then analyze the relationship between IoT and Big Data, specifically the drilldown of how the 4Vs of Big Data (Volume, Variety,...
Cloud computing is being adopted in one form or another by 94% of enterprises today. Tens of billions of new devices are being connected to The Internet of Things. And Big Data is driving this bus. An exponential increase is expected in the amount of information being processed, managed, analyzed, and acted upon by enterprise IT. This amazing is not part of some distant future - it is happening today. One report shows a 650% increase in enterprise data by 2020. Other estimates are even higher....
For basic one-to-one voice or video calling solutions, WebRTC has proven to be a very powerful technology. Although WebRTC’s core functionality is to provide secure, real-time p2p media streaming, leveraging native platform features and server-side components brings up new communication capabilities for web and native mobile applications, allowing for advanced multi-user use cases such as video broadcasting, conferencing, and media recording.
Adobe is changing the world though digital experiences. Adobe helps customers develop and deliver high-impact experiences that differentiate brands, build loyalty, and drive revenue across every screen, including smartphones, computers, tablets and TVs. Adobe content solutions are used daily by millions of companies worldwide-from publishers and broadcasters, to enterprises, marketing agencies and household-name brands. Building on its established design leadership, Adobe enables customers not o...