Welcome!

Java IoT Authors: Elizabeth White, Pat Romanski, David Bermingham, Charlotte Spencer-Smith, Tim Hinds

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
With an estimated 50 billion devices connected to the Internet by 2020, several industries will begin to expand their capabilities for retaining end point data at the edge to better utilize the range of data types and sheer volume of M2M data generated by the Internet of Things. In his session at @ThingsExpo, Don DeLoach, CEO and President of Infobright, will discuss the infrastructures businesses will need to implement to handle this explosion of data by providing specific use cases for filte...
Fortunately, meaningful and tangible business cases for IoT are plentiful in a broad array of industries and vertical markets. These range from simple warranty cost reduction for capital intensive assets, to minimizing downtime for vital business tools, to creating feedback loops improving product design, to improving and enhancing enterprise customer experiences. All of these business cases, which will be briefly explored in this session, hinge on cost effectively extracting relevant data from ...
SYS-CON Events announced today that VAI, a leading ERP software provider, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. VAI (Vormittag Associates, Inc.) is a leading independent mid-market ERP software developer renowned for its flexible solutions and ability to automate critical business functions for the distribution, manufacturing, specialty retail and service sectors. An IBM Premier Business Part...
SYS-CON Events announced today that Alert Logic, Inc., the leading provider of Security-as-a-Service solutions for the cloud, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Alert Logic, Inc., provides Security-as-a-Service for on-premises, cloud, and hybrid infrastructures, delivering deep security insight and continuous protection for customers at a lower cost than traditional security solutions. Ful...
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2015 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 ad...
As enterprises work to take advantage of Big Data technologies, they frequently become distracted by product-level decisions. In most new Big Data builds this approach is completely counter-productive: it presupposes tools that may not be a fit for development teams, forces IT to take on the burden of evaluating and maintaining unfamiliar technology, and represents a major up-front expense. In his session at @BigDataExpo at @ThingsExpo, Andrew Warfield, CTO and Co-Founder of Coho Data, will dis...
SYS-CON Events announced today that Commvault, a global leader in enterprise data protection and information management, has been named “Bronze Sponsor” of SYS-CON's 18th International Cloud Expo, which will take place on June 7–9, 2016, at the Javits Center in New York City, NY, and the 19th International Cloud Expo, which will take place on November 1–3, 2016, at the Santa Clara Convention Center in Santa Clara, CA. Commvault is a leading provider of data protection and information management...
The cloud promises new levels of agility and cost-savings for Big Data, data warehousing and analytics. But it’s challenging to understand all the options – from IaaS and PaaS to newer services like HaaS (Hadoop as a Service) and BDaaS (Big Data as a Service). In her session at @BigDataExpo at @ThingsExpo, Hannah Smalltree, a director at Cazena, will provide an educational overview of emerging “as-a-service” options for Big Data in the cloud. This is critical background for IT and data profes...
With the Apple Watch making its way onto wrists all over the world, it’s only a matter of time before it becomes a staple in the workplace. In fact, Forrester reported that 68 percent of technology and business decision-makers characterize wearables as a top priority for 2015. Recognizing their business value early on, FinancialForce.com was the first to bring ERP to wearables, helping streamline communication across front and back office functions. In his session at @ThingsExpo, Kevin Roberts...
SYS-CON Events announced today that Fusion, a leading provider of cloud services, will exhibit at SYS-CON's 18th International Cloud Expo®, which will take place on June 7-9, 2016, at the Javits Center in New York City, NY. Fusion, a leading provider of integrated cloud solutions to small, medium and large businesses, is the industry's single source for the cloud. Fusion's advanced, proprietary cloud service platform enables the integration of leading edge solutions in the cloud, including clou...
Most people haven’t heard the word, “gamification,” even though they probably, and perhaps unwittingly, participate in it every day. Gamification is “the process of adding games or game-like elements to something (as a task) so as to encourage participation.” Further, gamification is about bringing game mechanics – rules, constructs, processes, and methods – into the real world in an effort to engage people. In his session at @ThingsExpo, Robert Endo, owner and engagement manager of Intrepid D...
Eighty percent of a data scientist’s time is spent gathering and cleaning up data, and 80% of all data is unstructured and almost never analyzed. Cognitive computing, in combination with Big Data, is changing the equation by creating data reservoirs and using natural language processing to enable analysis of unstructured data sources. This is impacting every aspect of the analytics profession from how data is mined (and by whom) to how it is delivered. This is not some futuristic vision: it's ha...
WebRTC has had a real tough three or four years, and so have those working with it. Only a few short years ago, the development world were excited about WebRTC and proclaiming how awesome it was. You might have played with the technology a couple of years ago, only to find the extra infrastructure requirements were painful to implement and poorly documented. This probably left a bitter taste in your mouth, especially when things went wrong.
Learn how IoT, cloud, social networks and last but not least, humans, can be integrated into a seamless integration of cooperative organisms both cybernetic and biological. This has been enabled by recent advances in IoT device capabilities, messaging frameworks, presence and collaboration services, where devices can share information and make independent and human assisted decisions based upon social status from other entities. In his session at @ThingsExpo, Michael Heydt, founder of Seamless...
The IoT's basic concept of collecting data from as many sources possible to drive better decision making, create process innovation and realize additional revenue has been in use at large enterprises with deep pockets for decades. So what has changed? In his session at @ThingsExpo, Prasanna Sivaramakrishnan, Solutions Architect at Red Hat, discussed the impact commodity hardware, ubiquitous connectivity, and innovations in open source software are having on the connected universe of people, thi...
WebRTC: together these advances have created a perfect storm of technologies that are disrupting and transforming classic communications models and ecosystems. In his session at WebRTC Summit, Cary Bran, VP of Innovation and New Ventures at Plantronics and PLT Labs, provided an overview of this technological shift, including associated business and consumer communications impacts, and opportunities it may enable, complement or entirely transform.
There are so many tools and techniques for data analytics that even for a data scientist the choices, possible systems, and even the types of data can be daunting. In his session at @ThingsExpo, Chris Harrold, Global CTO for Big Data Solutions for EMC Corporation, showed how to perform a simple, but meaningful analysis of social sentiment data using freely available tools that take only minutes to download and install. Participants received the download information, scripts, and complete end-t...
For manufacturers, the Internet of Things (IoT) represents a jumping-off point for innovation, jobs, and revenue creation. But to adequately seize the opportunity, manufacturers must design devices that are interconnected, can continually sense their environment and process huge amounts of data. As a first step, manufacturers must embrace a new product development ecosystem in order to support these products.
Manufacturing connected IoT versions of traditional products requires more than multiple deep technology skills. It also requires a shift in mindset, to realize that connected, sensor-enabled “things” act more like services than what we usually think of as products. In his session at @ThingsExpo, David Friedman, CEO and co-founder of Ayla Networks, discussed how when sensors start generating detailed real-world data about products and how they’re being used, smart manufacturers can use the dat...
When it comes to IoT in the enterprise, namely the commercial building and hospitality markets, a benefit not getting the attention it deserves is energy efficiency, and IoT’s direct impact on a cleaner, greener environment when installed in smart buildings. Until now clean technology was offered piecemeal and led with point solutions that require significant systems integration to orchestrate and deploy. There didn't exist a 'top down' approach that can manage and monitor the way a Smart Buildi...