Click here to close now.

Welcome!

Industrial IoT Authors: Carmen Gonzalez, Pat Romanski, JP Morgenthal, AppDynamics Blog, Elizabeth White

Related Topics: Java IoT, Industrial IoT, @MicroservicesE Blog, Eclipse, IoT User Interface, Apache

Java IoT: Article

The Disruptor Framework: A Concurrency Framework for Java

Rediscovering the Producer-Consumer Model with the Disruptor

Let's start with the basic question: What is the disruptor? The disruptor is a concurrency framework for Java that allows data sharing between threads. The age old way of coding a producer-consumer model is to use a queue as the buffer area between the producer and the consumer, where the producer adds data objects to the queue, which are in turn processed by the consumer. However, such a model does not work well at the hardware level and ends up being highly inefficient. The disruptor in its simplest form replaces the queue with a data structure known as the ‘ring buffer'. Which brings us to the next question, what is the ring buffer? The ring buffer is an array of fixed length (which must be a power of 2), it's circular and wraps. This data structure is at the core of what makes the disruptor super fast.

Let's explore a simple everyday scenario in enterprise architectures. A producer (let's call it the publisher) creates data and stores it in the queue. Two immediate consumers (let's call them fooHandler and barHandler) consume the data and make updates to it. Once these 2 processors are done with a piece of data, it is then passed on to a third consumer (let's call it fooBarHandler) for further processing. In a concurrent processing system using legacy techniques, coding this architecture would involve a crisscross of queues and numerous concurrency challenges, such as dealing with locks, CAS, write contention, etc. The disruptor on the other hand immensely simplifies such a scenario by providing a simple API for creating the producer, consumers and ring buffer, which in turn relieve the developer of all concerns surrounding handling concurrency and doing so in an efficient manner. We shall now explore how the disruptor works its magic and provides a reliable messaging framework.

Writing to the ring buffer

Looking at the figure above, we find ourselves in the middle of the action. The ring buffer is an array of length 4 and is populated with data items - 4,5,6 and 7, which in the case of the disruptor are known as events. The square above the ring buffer containing the number 7 is the current sequence number, which denotes the highest populated event in the ring buffer. The ring buffer keeps track of this sequence number and increments it as and when new events are published to it. The fooHandler, barHandler and fooBarHandler are the consumers, which in disruptor terminology are called ‘event processors'. Each of these also has a square containing a sequence number, which in the case of the event processors denotes the highest event that they have consumed/processed so far. Thus its apparent that each entity (except the publisher) tracks its own sequence number and thus does not need to rely on a third party to figure out which is the next event its after.

The publisher asks the ring buffer for the next sequence number. The ring buffer is currently at 7, so the next sequence number would be 8. However, this would also entail overwriting the event with sequence number 4 (since there are only 4 slots in the array and the oldest event gets replaced with the newest one). The ring buffer first checks the most downstream consumer (fooBarHandler) to determine whether it is done processing the event with sequence number 4. In this case, it has, so it returns the number 8 to the publisher. In case fooBarHandler was stuck at a sequence number lower than 4, the ring buffer would have waited for it to finish processing the 4th event before returning the next sequence number to the publisher. This sequence number helps the publisher identify the next available slot in the ring buffer by performing a simple mod operation. indexOfNextAvailableSlot = highestSeqNo%longthOfRingBuffer, which in this case is 0 (8%4). The publisher then claims the next slot in the ring buffer (via a customizable strategy depending on whether there is a single or multiple publishers), which is currently occupied by event 4, and publishes event 8 to it.

Reading from the ring buffer by immediate consumers

The figure above shows the state of operations after the publisher has published event 8 to the ring buffer. The ring buffer's sequence number has been updated to 8 and now contains events 5,6,7 and 8. We see that foohandler, which has processed events upto 7, has been waiting (using a customizable strategy) for the 8th event to be published. Unlike the publisher though, it does not directly communicate with the ring buffer, but uses an entity known as the ‘sequence barrier' to do so on its behalf. The sequence barrier let's fooHandler know that the highest sequence number available in the ring buffer is now 8. FooHandler may now get this event and process it.

Similarly, barHandler checks the sequence barrier to determine whether there are any more events it can process. However, rather than just telling barHandler that the next (6th) event is up for grabs, the sequence barrier returns the highest sequence number present in the ring buffer to barHandler too. This way, barHandler can grab events 6,7,8 and process them in a batch before it has to enquire about further events being published. This saves time and reduces load.

Another important thing to note here is that in the case of multiple event processors, any given field in the event object must only be written to by any one event processor. Doing so prevents write contention, and thus removes the need for locks or CAS.

Reading from the ring buffer by downstream consumers

A few moments after the set of immediate consumers grab the next set of data, the state of affairs looks like the figure above. fooHandler is done processing all 8 available events (and has accordingly updated its sequence number to 8), whereas barHandler, being the slow coach that it is, has only processed events upto number 6 (and thus has updated sequence number to 6). We now see that fooBarHandler, which was done processing events upto number 5 at the start of our examination, is still waiting for an event higher than that to process. Why did its sequence barrier not inform it once event 8 was published to the ring buffer? Well, that is because downstream consumers don't automatically get notified of the highest sequence number present in the ring buffer. Their sequence barriers on the other hand determine the next sequence number they can process by calculating the minimum sequence number that the set of event processors directly before them have processed. This helps ensure that the downstream consumers only act on an event once its processing has been completed by the entire set of upstream consumers. The sequence barrier examines the sequence number on fooHandler (which is 8) and the sequence number on barHandler (which is 6) and decides that event 6 is the highest event that fooBarHandler can process. It returns this info to fooBarHandler, which then grabs event 6 and processes it. It must be noted that even in the case of the downstream consumers, they grab the events directly from the ring buffer and not from the consumers before them.

Well, that is about all you would need to know about the working of the disruptor framework to get started. But while this is all well and good in theory, the question still remains, how would one code the above architecture using the disruptor library? The answer to that question lies below.

Coding the disruptor

public final class FooBarEvent {
private double foo=0;
private double bar=0;
public double getFoo(){
return foo;
}
public double getBar() {
return bar;
}
public void setFoo(final double foo) {
this.foo = foo;
}
public void setBar(final double bar) {
this.bar = bar;
}
public final static EventFactory<FooBarEvent> EVENT_FACTORY
= new EventFactory<FooBarEvent>() {
public FooBarEvent newInstance() {
return new FooBarEvent();
}
};
}

The class FooBarEvent, as the name suggests, acts as the event object which is published by the publisher to the ring buffer and consumed by the eventProcessors - fooHandler, barHandler and fooBarHandler. It contains two fields ‘foo' and ‘bar' of type double, along with their corresponding setters/getters. It also contains an entity ‘EVENT_FACTORY' of type EventFactory, which is used to create an instance of this event.

public class FooBarDisruptor {           
public static final int RING_SIZE=4;
public static final ExecutorService EXECUTOR
=Executors.newCachedThreadPool();

final EventTranslator<FooBarEvent> eventTranslator
=new EventTranslator<FooBarEvent>() {
public void translateTo(FooBarEvent event,
long sequence) {
double foo=event.getFoo();
double bar=event.getBar();
system.out.println("foo="+foo
+", bar="+bar
+" (sequence="+sequence+")");
}
};

final EventHandler<FooBarEvent> fooHandler
= new EventHandler<FooBarEvent>() {
public void onEvent(final FooBarEvent event,
final long sequence,
final boolean endOfBatch)
throws Exception {
double foo=Math.random();
event.setFoo(foo);
System.out.println("setting foo to "+foo
+" (sequence="+sequence+")");
}
};

final EventHandler<FooBarEvent> barHandler
= new EventHandler<FooBarEvent>() {
public void onEvent(final FooBarEvent event,
final long sequence,
final boolean endOfBatch)
throws Exception {
double bar=Math.random();
event.setBar(bar);
System.out.println("setting bar to "+bar
+" (sequence="+sequence+")");
}
};

final EventHandler<FooBarEvent> fooBarHandler
= new EventHandler<FooBarEvent>() {
public void onEvent(final FooBarEvent event,
final long sequence,
final boolean endOfBatch)
throws Exception {
double foo=event.getFoo();
double bar=event.getBar();
System.out.println("foo="+foo
+", bar="+bar
+" (sequence="+sequence+")");
}
};

public Disruptor setup() {
Disruptor<FooBarEvent> disruptor =
new Disruptor<FooBarEvent>(FooBarEvent.EVENT_FACTORY,
EXECUTOR,
new SingleThreadedClaimStrategy(RING_SIZE),
new SleepingWaitStrategy());
disruptor.handleEventsWith(fooHandler, barHandler).then(fooBarHandler);
RingBuffer<FooBarEvent> ringBuffer = disruptor.start();             
return disruptor;
}

public void publish(Disruptor<FooBarEvent> disruptor) {
for(int i=0;i<1000;i++) {
disruptor.publishEvent(eventTranslator);
}
}

public static void main(String[] args) {
FooBarDisruptor fooBarDisruptor=new FooBarDisruptor();
Disruptor disruptor=fooBarDisruptor.setup();
fooBarDisruptor.publish(disruptor);
}
}

The class FooBarDisruptor is where all the action happens. The ‘eventTranslator' is an entity which aids the publisher in publishing events to the ring buffer. It implements a method ‘translateTo' which gets invoked when the publisher is granted permission to publish the next event. fooHandler, barHandler and fooBarHandler are the event processors, and are objects of type ‘EventHandler'. Each of them implements a method ‘onEvent' which gets invoked once the event processor is granted access to a new event. The method ‘setup' is responsible for creating the disruptor, assigning the corresponding event handlers, and setting the dependency rules amongst them. The method ‘publish' is responsible for publishing a thousand events of the type ‘FooBarEvent' to the ring buffer.

In order to get the above code to work, you must download the disruptor jar file from http://code.google.com/p/disruptor/downloads/list and include the same in your classpath.

Conclusion
The disruptor is currently in use in the ultra efficient LMAX architecture, where it has proven to be a reliable model for inter thread communication and data sharing, reducing the end to end latency to a fraction of what queue based architectures provided. It does so using a variety of techniques, including replacing the array blocking queue with a ring buffer, getting rid of all locks, write contention and CAS operations (except in the scenario where one has multiple publishers), having each entity track its own progress by way of a sequence number, etc. Adopting this framework can greatly boost a developer's productivity in terms of coding a producer-consumer pattern, while at the same time aid in creating an end product far superior in terms of both design and performance to the legacy queue based architectures.

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
17th Cloud Expo, taking place Nov 3-5, 2015, 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 enterprises are using some form of XaaS – software, platform, and infrastructure as a service.
The recent trends like cloud computing, social, mobile and Internet of Things are forcing enterprises to modernize in order to compete in the competitive globalized markets. However, enterprises are approaching newer technologies with a more silo-ed way, gaining only sub optimal benefits. The Modern Enterprise model is presented as a newer way to think of enterprise IT, which takes a more holistic approach to embracing modern technologies.
The true value of the Internet of Things (IoT) lies not just in the data, but through the services that protect the data, perform the analysis and present findings in a usable way. With many IoT elements rooted in traditional IT components, Big Data and IoT isn’t just a play for enterprise. In fact, the IoT presents SMBs with the prospect of launching entirely new activities and exploring innovative areas. CompTIA research identifies several areas where IoT is expected to have the greatest impact.
There's no doubt that the Internet of Things is driving the next wave of innovation. Google has spent billions over the past few months vacuuming up companies that specialize in smart appliances and machine learning. Already, Philips light bulbs, Audi automobiles, and Samsung washers and dryers can communicate with and be controlled from mobile devices. To take advantage of the opportunities the Internet of Things brings to your business, you'll want to start preparing now.
P2P RTC will impact the landscape of communications, shifting from traditional telephony style communications models to OTT (Over-The-Top) cloud assisted & PaaS (Platform as a Service) communication services. The P2P shift will impact many areas of our lives, from mobile communication, human interactive web services, RTC and telephony infrastructure, user federation, security and privacy implications, business costs, and scalability. In his session at @ThingsExpo, Robin Raymond, Chief Architect at Hookflash, will walk through the shifting landscape of traditional telephone and voice services ...
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...
The world is at a tipping point where the technology, the device and global adoption are converging to such a point that we will see an explosion of a world where smartphone devices not only allow us to talk to each other, but allow for communication between everything – serving as a central hub from which we control our world – MediaTek is at the heart of both driving this and allowing the markets to drive this reality forward themselves. The next wave of consumer gadgets is here – smart, connected, and small. If your ambitions are big, so are ours. In his session at @ThingsExpo, Jack Hu, D...
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...
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. With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo, June 9-11, 2015, at the Javits Center in New York City. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be
SYS-CON Events announced today that MetraTech, now part of Ericsson, 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. Ericsson is the driving force behind the Networked Society- a world leader in communications infrastructure, software and services. Some 40% of the world’s mobile traffic runs through networks Ericsson has supplied, serving more than 2.5 billion subscribers.
The 4th International Internet of @ThingsExpo, co-located with the 17th International Cloud Expo - to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA - announces that its Call for Papers is open. The Internet of Things (IoT) is the biggest idea since the creation of the Worldwide Web more than 20 years ago.
SYS-CON Events announced today that O'Reilly Media has been named “Media 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 City, NY. O'Reilly Media spreads the knowledge of innovators through its books, online services, magazines, and conferences. Since 1978, O'Reilly Media has been a chronicler and catalyst of cutting-edge development, homing in on the technology trends that really matter and spurring their adoption by amplifying "faint signals" from the alpha geeks who are creating the future. An active participa...
We’re entering a new era of computing technology that many are calling the Internet of Things (IoT). Machine to machine, machine to infrastructure, machine to environment, the Internet of Everything, the Internet of Intelligent Things, intelligent systems – call it what you want, but it’s happening, and its potential is huge. IoT is comprised of smart machines interacting and communicating with other machines, objects, environments and infrastructures. As a result, huge volumes of data are being generated, and that data is being processed into useful actions that can “command and control” thi...
There will be 150 billion connected devices by 2020. New digital businesses have already disrupted value chains across every industry. APIs are at the center of the digital business. You need to understand what assets you have that can be exposed digitally, what their digital value chain is, and how to create an effective business model around that value chain to compete in this economy. No enterprise can be complacent and not engage in the digital economy. Learn how to be the disruptor and not the disruptee.
Buzzword alert: Microservices and IoT at a DevOps conference? What could possibly go wrong? In this Power Panel at DevOps Summit, moderated by Jason Bloomberg, the leading expert on architecting agility for the enterprise and president of Intellyx, panelists will peel away the buzz and discuss the important architectural principles behind implementing IoT solutions for the enterprise. As remote IoT devices and sensors become increasingly intelligent, they become part of our distributed cloud environment, and we must architect and code accordingly. At the very least, you'll have no problem fil...
There's Big Data, then there's really Big Data from the Internet of Things. IoT is evolving to include many data possibilities like new types of event, log and network data. The volumes are enormous, generating tens of billions of logs per day, which raise data challenges. Early IoT deployments are relying heavily on both the cloud and managed service providers to navigate these challenges. In her session at Big Data Expo®, Hannah Smalltree, Director at Treasure Data, discussed how IoT, Big Data and deployments are processing massive data volumes from wearables, utilities and other machines...
With major technology companies and startups seriously embracing IoT strategies, now is the perfect time to attend @ThingsExpo in Silicon Valley. Learn what is going on, contribute to the discussions, and ensure that your enterprise is as "IoT-Ready" as it can be! Internet of @ThingsExpo, taking place Nov 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, is co-located with 17th Cloud Expo and will feature technical sessions from a rock star conference faculty and the leading industry players in the world. The Internet of Things (IoT) is the most profound change in personal an...
The worldwide cellular network will be the backbone of the future IoT, and the telecom industry is clamoring to get on board as more than just a data pipe. In his session at @ThingsExpo, Evan McGee, CTO of Ring Plus, Inc., discussed what service operators can offer that would benefit IoT entrepreneurs, inventors, and consumers. Evan McGee is the CTO of RingPlus, a leading innovative U.S. MVNO and wireless enabler. His focus is on combining web technologies with traditional telecom to create a new breed of unified communication that is easily accessible to the general consumer. With over a de...
Disruptive macro trends in technology are impacting and dramatically changing the "art of the possible" relative to supply chain management practices through the innovative use of IoT, cloud, machine learning and Big Data to enable connected ecosystems of engagement. Enterprise informatics can now move beyond point solutions that merely monitor the past and implement integrated enterprise fabrics that enable end-to-end supply chain visibility to improve customer service delivery and optimize supplier management. Learn about enterprise architecture strategies for designing connected systems tha...
From telemedicine to smart cars, digital homes and industrial monitoring, the explosive growth of IoT has created exciting new business opportunities for real time calls and messaging. In his session at @ThingsExpo, Ivelin Ivanov, CEO and Co-Founder of Telestax, shared some of the new revenue sources that IoT created for Restcomm – the open source telephony platform from Telestax. Ivelin Ivanov is a technology entrepreneur who founded Mobicents, an Open Source VoIP Platform, to help create, deploy, and manage applications integrating voice, video and data. He is the co-founder of TeleStax, a...