Welcome!

Java Authors: Elizabeth White, Torben Andersen, Liz McMillan, Patrick Carey, Srinivasan Sundara Rajan

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
The BPM world is going through some evolution or changes where traditional business process management solutions really have nowhere to go in terms of development of the road map. In this demo at 15th Cloud Expo, Kyle Hansen, Director of Professional Services at AgilePoint, shows AgilePoint’s unique approach to dealing with this market circumstance by developing a rapid application composition or development framework.
“In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, 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...
"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.
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.
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...

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...

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...
DevOps Summit 2015 New York, 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 widespread success of cloud computing is driving the DevOps revolution in enterprise IT. Now as never before, development teams must communicate and collaborate in a dynamic, 24/7/365 environment. There is no time to wait for long development cycles that produce software that is obsolete at launch. DevOps may be disruptive, but it is essential.
"People are a lot more knowledgeable about APIs now. There are two types of people who work with APIs - IT people who want to use APIs for something internal and the product managers who want to do something outside APIs for people to connect to them," explained Roberto Medrano, Executive Vice President at SOA Software, in this SYS-CON.tv interview at Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
Nigeria has the largest economy in Africa, at more than US$500 billion, and ranks 23rd in the world. A recent re-evaluation of Nigeria's true economic size doubled the previous estimate, and brought it well ahead of South Africa, which is a member (unlike Nigeria) of the G20 club for political as well as economic reasons. Nigeria's economy can be said to be quite diverse from one point of view, but heavily dependent on oil and gas at the same time. Oil and natural gas account for about 15% of Nigera's overall economy, but traditionally represent more than 90% of the country's exports and as...
The Internet of Things is a misnomer. That implies that everything is on the Internet, and that simply should not be - especially for things that are blurring the line between medical devices that stimulate like a pacemaker and quantified self-sensors like a pedometer or pulse tracker. The mesh of things that we manage must be segmented into zones of trust for sensing data, transmitting data, receiving command and control administrative changes, and peer-to-peer mesh messaging. In his session at @ThingsExpo, Ryan Bagnulo, Solution Architect / Software Engineer at SOA Software, focused on desi...
"At our booth we are showing how to provide trust in the Internet of Things. Trust is where everything starts to become secure and trustworthy. Now with the scaling of the Internet of Things it becomes an interesting question – I've heard numbers from 200 billion devices next year up to a trillion in the next 10 to 15 years," explained Johannes Lintzen, Vice President of Sales at Utimaco, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
"For over 25 years we have been working with a lot of enterprise customers and we have seen how companies create applications. And now that we have moved to cloud computing, mobile, social and the Internet of Things, we see that the market needs a new way of creating applications," stated Jesse Shiah, CEO, President and Co-Founder of AgilePoint Inc., in this SYS-CON.tv interview at 15th Cloud Expo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
SYS-CON Events announced today that Gridstore™, the leader in hyper-converged infrastructure purpose-built to optimize Microsoft workloads, 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. Gridstore™ is the leader in hyper-converged infrastructure purpose-built for Microsoft workloads and designed to accelerate applications in virtualized environments. Gridstore’s hyper-converged infrastructure is the industry’s first all flash version of HyperConverged Appliances that include both compute and storag...
Today’s enterprise is being driven by disruptive competitive and human capital requirements to provide enterprise application access through not only desktops, but also mobile devices. To retrofit existing programs across all these devices using traditional programming methods is very costly and time consuming – often prohibitively so. In his session at @ThingsExpo, Jesse Shiah, CEO, President, and Co-Founder of AgilePoint Inc., discussed how you can create applications that run on all mobile devices as well as laptops and desktops using a visual drag-and-drop application – and eForms-buildi...
We certainly live in interesting technological times. And no more interesting than the current competing IoT standards for connectivity. Various standards bodies, approaches, and ecosystems are vying for mindshare and positioning for a competitive edge. It is clear that when the dust settles, we will have new protocols, evolved protocols, that will change the way we interact with devices and infrastructure. We will also have evolved web protocols, like HTTP/2, that will be changing the very core of our infrastructures. At the same time, we have old approaches made new again like micro-services...
Code Halos - aka "digital fingerprints" - are the key organizing principle to understand a) how dumb things become smart and b) how to monetize this dynamic. In his session at @ThingsExpo, Robert Brown, AVP, Center for the Future of Work at Cognizant Technology Solutions, outlined research, analysis and recommendations from his recently published book on this phenomena on the way leading edge organizations like GE and Disney are unlocking the Internet of Things opportunity and what steps your organization should be taking to position itself for the next platform of digital competition.
The 3rd International Internet of @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 its Call for Papers is now open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
As the Internet of Things unfolds, mobile and wearable devices are blurring the line between physical and digital, integrating ever more closely with our interests, our routines, our daily lives. Contextual computing and smart, sensor-equipped spaces bring the potential to walk through a world that recognizes us and responds accordingly. We become continuous transmitters and receivers of data. In his session at @ThingsExpo, Andrew Bolwell, Director of Innovation for HP's Printing and Personal Systems Group, discussed how key attributes of mobile technology – touch input, sensors, social, and ...