Welcome!

Java Authors: Patrick Carey, Jack Newton, ChandraShekar Dattatreya, Brian Vandegrift, Gil Allouche

Related Topics: Java

Java: 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
Bit6 today issued a challenge to the technology community implementing Web Real Time Communication (WebRTC). To leap beyond WebRTC’s significant limitations and fully leverage its underlying value to accelerate innovation, application developers need to consider the entire communications ecosystem.
The definition of IoT is not new, in fact it’s been around for over a decade. What has changed is the public's awareness that the technology we use on a daily basis has caught up on the vision of an always on, always connected world. If you look into the details of what comprises the IoT, you’ll see that it includes everything from cloud computing, Big Data analytics, “Things,” Web communication, applications, network, storage, etc. It is essentially including everything connected online from hardware to software, or as we like to say, it’s an Internet of many different things. The difference ...
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world.
SYS-CON Events announced today that Windstream, a leading provider of advanced network and cloud communications, has been named “Silver Sponsor” of SYS-CON's 16th International Cloud Expo®, which will take place on June 9–11, 2015, at the Javits Center in New York, NY. Windstream (Nasdaq: WIN), a FORTUNE 500 and S&P 500 company, is a leading provider of advanced network communications, including cloud computing and managed services, to businesses nationwide. The company also offers broadband, phone and digital TV services to consumers primarily in rural areas.
"There is a natural synchronization between the business models, the IoT is there to support ,” explained Brendan O'Brien, Co-founder and Chief Architect of Aria Systems, in this SYS-CON.tv interview at the 15th International Cloud Expo®, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
The major cloud platforms defy a simple, side-by-side analysis. Each of the major IaaS public-cloud platforms offers their own unique strengths and functionality. Options for on-site private cloud are diverse as well, and must be designed and deployed while taking existing legacy architecture and infrastructure into account. Then the reality is that most enterprises are embarking on a hybrid cloud strategy and programs. In this Power Panel at 15th Cloud Expo (http://www.CloudComputingExpo.com), moderated by Ashar Baig, Research Director, Cloud, at Gigaom Research, Nate Gordon, Director of T...
An entirely new security model is needed for the Internet of Things, or is it? Can we save some old and tested controls for this new and different environment? In his session at @ThingsExpo, New York's at the Javits Center, Davi Ottenheimer, EMC Senior Director of Trust, reviewed hands-on lessons with IoT devices and reveal a new risk balance you might not expect. Davi Ottenheimer, EMC Senior Director of Trust, has more than nineteen years' experience managing global security operations and assessments, including a decade of leading incident response and digital forensics. He is co-author of t...

ARMONK, N.Y., Nov. 20, 2014 /PRNewswire/ --  IBM (NYSE: IBM) today announced that it is bringing a greater level of control, security and flexibility to cloud-based application development and delivery with a single-tenant version of Bluemix, IBM's platform-as-a-service. The new platform enables developers to build ap...

Explosive growth in connected devices. Enormous amounts of data for collection and analysis. Critical use of data for split-second decision making and actionable information. All three are factors in making the Internet of Things a reality. Yet, any one factor would have an IT organization pondering its infrastructure strategy. How should your organization enhance its IT framework to enable an Internet of Things implementation? In his session at Internet of @ThingsExpo, James Kirkland, Chief Architect for the Internet of Things and Intelligent Systems at Red Hat, described how to revolutioniz...
Technology is enabling a new approach to collecting and using data. This approach, commonly referred to as the "Internet of Things" (IoT), enables businesses to use real-time data from all sorts of things including machines, devices and sensors to make better decisions, improve customer service, and lower the risk in the creation of new revenue opportunities. In his General Session at Internet of @ThingsExpo, Dave Wagstaff, Vice President and Chief Architect at BSQUARE Corporation, discuss the real benefits to focus on, how to understand the requirements of a successful solution, the flow of ...
The security devil is always in the details of the attack: the ones you've endured, the ones you prepare yourself to fend off, and the ones that, you fear, will catch you completely unaware and defenseless. The Internet of Things (IoT) is nothing if not an endless proliferation of details. It's the vision of a world in which continuous Internet connectivity and addressability is embedded into a growing range of human artifacts, into the natural world, and even into our smartphones, appliances, and physical persons. In the IoT vision, every new "thing" - sensor, actuator, data source, data con...
"BSQUARE is in the business of selling software solutions for smart connected devices. It's obvious that IoT has moved from being a technology to being a fundamental part of business, and in the last 18 months people have said let's figure out how to do it and let's put some focus on it, " explained Dave Wagstaff, VP & Chief Architect, at BSQUARE Corporation, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4-6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Focused on this fast-growing market’s needs, Vitesse Semiconductor Corporation (Nasdaq: VTSS), a leading provider of IC solutions to advance "Ethernet Everywhere" in Carrier, Enterprise and Internet of Things (IoT) networks, introduced its IStaX™ software (VSC6815SDK), a robust protocol stack to simplify deployment and management of Industrial-IoT network applications such as Industrial Ethernet switching, surveillance, video distribution, LCD signage, intelligent sensors, and metering equipment. Leveraging technologies proven in the Carrier and Enterprise markets, IStaX is designed to work ac...
C-Labs LLC, a leading provider of remote and mobile access for the Internet of Things (IoT), announced the appointment of John Traynor to the position of chief operating officer. Previously a strategic advisor to the firm, Mr. Traynor will now oversee sales, marketing, finance, and operations. Mr. Traynor is based out of the C-Labs office in Redmond, Washington. He reports to Chris Muench, Chief Executive Officer. Mr. Traynor brings valuable business leadership and technology industry expertise to C-Labs. With over 30 years' experience in the high-tech sector, John Traynor has held numerous...
The 3rd International @ThingsExpo, co-located with the 16th International Cloud Expo - to be held June 9-11, 2015, at the Javits Center in New York City, NY - announces that it is now accepting Keynote Proposals. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago. All major researchers estimate there will be tens of billions devices - computers, smartphones, tablets, and sensors - connected to the Internet by 2020. This number will continue to grow at a rapid pace for the next several decades.
The Internet of Things is not new. Historically, smart businesses have used its basic concept of leveraging data to drive better decision making and have capitalized on those insights to realize additional revenue opportunities. So, what has changed to make the Internet of Things one of the hottest topics in tech? In his session at @ThingsExpo, Chris Gray, Director, Embedded and Internet of Things, discussed the underlying factors that are driving the economics of intelligent systems. Discover how hardware commoditization, the ubiquitous nature of connectivity, and the emergence of Big Data a...
Almost everyone sees the potential of Internet of Things but how can businesses truly unlock that potential. The key will be in the ability to discover business insight in the midst of an ocean of Big Data generated from billions of embedded devices via Systems of Discover. Businesses will also need to ensure that they can sustain that insight by leveraging the cloud for global reach, scale and elasticity.
SYS-CON Events announced today that IDenticard will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. IDenticard™ is the security division of Brady Corp (NYSE: BRC), a $1.5 billion manufacturer of identification products. We have small-company values with the strength and stability of a major corporation. IDenticard offers local sales, support and service to our customers across the United States and Canada. Our partner network encompasses some 300 of the world's leading systems integrators and security s...
IoT is still a vague buzzword for many people. In his session at @ThingsExpo, Mike Kavis, Vice President & Principal Cloud Architect at Cloud Technology Partners, discussed the business value of IoT that goes far beyond the general public's perception that IoT is all about wearables and home consumer services. He also discussed how IoT is perceived by investors and how venture capitalist access this space. Other topics discussed were barriers to success, what is new, what is old, and what the future may hold. Mike Kavis is Vice President & Principal Cloud Architect at Cloud Technology Pa...
Cloud Expo 2014 TV commercials will feature @ThingsExpo, which was launched in June, 2014 at New York City's Javits Center as the largest 'Internet of Things' event in the world. The next @ThingsExpo will take place November 4-6, 2014, at the Santa Clara Convention Center, in Santa Clara, California. Since its launch in 2008, Cloud Expo TV commercials have been aired and CNBC, Fox News Network, and Bloomberg TV. Please enjoy our 2014 commercial.