Click here to close now.

Welcome!

Java IoT Authors: Lori MacVittie, Elizabeth White, Liz McMillan, Dinko Eror, Gregor Petri

Related Topics: IoT User Interface

IoT User Interface: Article

Enterprise Comet: Awaken the Grizzly!

The real deal

There's a common misconception among many end users, consumers, and developers that AJAX is the ultimate solution for the Web and that it can provide all the same functionality as a rich desktop solution. Sure, AJAX can cover most of our expectations for a rich client, mimicking functionality provided by a desktop application, but there's still one area that has yet to be fully integrated ­ scalable server-initiated message delivery.

With server-initiated message delivery, all end users of a particular application are simultaneously notified of any changes to the application state, e.g., at the stock exchange a stock is dropping fast and the trading application has to inform all traders about the sudden change in price.

Server-Initiated Message Delivery
Let's use the trading application as an example for server-initiated message delivery. Each broker has his own preferences in stocks and bonds and requires instant notification of changes in the market. A desktop client for a distributed enterprise application typically registers interest in specific kinds of server messages so the server can notify the desktop client when they occur. This lets the desktop application efficiently use the network on a need-to-know basis instead of having the client actively ask for information.

This approach won't work for a traditional Web-based AJAX application since the server can't initiate a direct connection to the browser because of browser security, firewalls, and Web proxies.

Sure, it's possible with AJAX to "notify" a Web client that a change has occurred on the server using a technique called "polling." By creating a Web application that polls every now and then the end user believes that he's been notified by the server, when in fact it's repeatedly asking for updates like any child asking for candy ­ Can I get it now? Can I get it now? Can I get it now? You get the picture.

Of course, this impacts network bandwidth since there's traffic for each polling request even when no updates are available from the server. We need a way for Web clients to register interest in certain types of messages and then let the server initiate delivery of those messages, pushing them to each browser.

There's a Twist
OK, OK, OK, there is a twist ­ you can't actually "push" messages to a Web-based AJAX application unless you maintain an open connection from the client to the server. However, a thread is kept alive on the server for each open connection so messages can be delivered to the browser immediately.

The fact that you'd even try to maintain an open connection per user to a server would have heads rolling down the corridors in most IT departments. Just imagine thousands, or even hundreds of thousands of connections, using the thread and process pooling models provided by most Web Servers today, keeping each thread alive on the server just to be able to send a message to the client ­ it doesn't scale! Let's come back to that one later.

HTTP Connection Limitations
Today most frameworks leveraging AJAX are using the XMLHttpRequest object, which allocates an HTTP connection for the duration of the request. The HTTP 1.1 specification recommends that browsers support a maximum of two open connections to the hosting server. This presents a problem for highly interactive AJAX Web applications, especially on Microsoft Internet Explorer, which enforces this recommendation.

If there are more than two AJAX frameworks or components using the XMLHttpRequest on the same Web page then there will probably be contention for the two open connections, causing requests to queue. The result will be blocked and ineffective communication, defeating the main purpose of having AJAX on the Web page. There's a need to share server communications over two HTTP connections at most.

Next-Generation Web Communication
The main reason a Web server allocates one thread per connection is because it expects the request to be highly active and short-lived. However, maintaining an open connection to the server is extremely long-lived and activity is mostly dormant. We also need a way to meaningfully share server communications to address the browser connection limit. Thankfully, there are several projects in process addressing the limitations of traditional AJAX Web applications. Let's have a look at some of these projects.

Comet - The Never-Ending Request
First we need a way to create message-driven Web applications that require the server to notify the client about server-side events. This is where Comet comes in as described by Wikipedia:
Comet is a programming technique that enables Web servers to send data to the client without having any need for the client to request it.

Comet provides the means for the server to initiate a response to a client request, and later send a message to that client using the same response ­ for example, in the browser a message will "just" appear. Comet also provides clients with a way to register interest in specific types of messages. When the server publishes a message, it's delivered only to clients that previously registered interest in that kind of message.

Comet doesn't solve everything; in fact it creates some new problems. Using Comet means lots of outstanding requests, ideally one per client, and introduces similar scalability issues at the server as the AJAX polling technique. Keeping a separate thread allocated for each open request will exhaust the server's resources, so for this model to work properly, the Web server has to handle multiple requests without allocating one thread per request.

Asynchronous Request Processing
The idea behind Asynchronous Request Processing (ARP) is to manage incoming servlet requests asynchronously. Rather than committing a separate Java thread to synchronously process each servlet request, a single thread leverages Java NIO to detect when new information needs to be written to the response of any outstanding request. This technique provides a huge scalability win for the Comet use case, giving excellent performance even when there are a large number of outstanding, mostly dormant, requests at the server.

Although there's no standard defined for ARP several teams and projects are providing ARP solutions, such as Jetty Continuations and Grizzly. We take our hats off to these visionary teams providing everyday developers with ARP and Comet solutions.

Note: There's hope that ARP will be standard in the Servlet 3.0 and Java EE 6 specifications.

The Comet Messaging Protocol
With Comet and ARP we now have the means to build message-driven Web applications but, as mentioned earlier, W3C recommends at most two active connections from the browser to the Web server at any one time. Therefore, we'd prefer to have a single active connection being used for Comet notifications, leaving the other connection free to download images, CSS, and JavaScript or communicate with the server. This requires a way to manage multiple logical channels of information over a single shared Comet notification response.


More Stories By Jonas Jacobi

Jonas has 21 years of experience leading the development of innovative technology products and services. Together with Kaazing’s Co-Founder & CTO John Fallows, he pioneered and championed the groundbreaking HTML5 WebSocket standard. Prior to co-founding Kaazing he served as VP of Product Management for Brane Corporation, a Silicon Valley startup dedicated to developing a market-leading enterprise platform for building model-driven apps. Before Brane, he spent 8+ years at Oracle where he served as a Java EE and open source Evangelist, and was Product Manager in the Oracle Application Server division for JavaServer Faces, Oracle ADF Faces, and Oracle ADF Faces Rich Client. He is a frequent speaker at international conferences on accelerating and scaling secure enterprise-grade WebComms (Web Communications).

More Stories By John Fallows

John brings to Kaazing his 17 years’ experience in technology development and software design, and is considered a pioneer in the field of rich and highly interactive user interfaces. As CTO he formulates Kaazing Corporation’s vision of enabling mobile users, marketplaces and machines to connect and communicate in real-time, more reliably and at unprecedented scale. He defines the architecture of the Kaazing product suite and oversees its development. Prior to co-founding Kaazing, John served as Architect for Brane Corporation, a startup company based in Redwood City, California. Before joining Brane, he was a Consulting Member of Technical Staff for Server Technologies at Oracle Corporation. During his last five years at Oracle, he focused on designing, developing, and evolving Oracle ADF Faces to fully integrate Ajax technologies. Originally from Northern Ireland, he received his MA in Computer Science from Cambridge University in the United Kingdom and has written several articles for leading IT magazines such as Java Developer’s Journal, AjaxWorld Magazine, and JavaMagazine (DE), and is a popular speaker at international conferences. He is co-author of the bestselling book Pro JSF and Ajax: Building Rich Internet Components (Apress).

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
Internet of Things (IoT) will be a hybrid ecosystem of diverse devices and sensors collaborating with operational and enterprise systems to create the next big application. In their session at @ThingsExpo, Bramh Gupta, founder and CEO of robomq.io, and Fred Yatzeck, principal architect leading product development at robomq.io, discussed how choosing the right middleware and integration strategy from the get-go will enable IoT solution developers to adapt and grow with the industry, while at the same time reduce Time to Market (TTM) by using plug and play capabilities offered by a robust IoT ...
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists addressed this very serious issue of profound change in the industry.
SYS-CON Events announced today that BMC 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. BMC delivers software solutions that help IT transform digital enterprises for the ultimate competitive business advantage. BMC has worked with thousands of leading companies to create and deliver powerful IT management services. From mainframe to cloud to mobile, BMC pairs high-speed digital innovation with robust IT industrialization – allowing customers to provide amazing user experiences with optimized IT per...
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.
Internet of Things is moving from being a hype to a reality. Experts estimate that internet connected cars will grow to 152 million, while over 100 million internet connected wireless light bulbs and lamps will be operational by 2020. These and many other intriguing statistics highlight the importance of Internet powered devices and how market penetration is going to multiply many times over in the next few years.
It is one thing to build single industrial IoT applications, but what will it take to build the Smart Cities and truly society-changing applications of the future? The technology won’t be the problem, it will be the number of parties that need to work together and be aligned in their motivation to succeed. In his session at @ThingsExpo, Jason Mondanaro, Director, Product Management at Metanga, discussed how you can plan to cooperate, partner, and form lasting all-star teams to change the world and it starts with business models and monetization strategies.
The Internet of Things is not only adding billions of sensors and billions of terabytes to the Internet. It is also forcing a fundamental change in the way we envision Information Technology. For the first time, more data is being created by devices at the edge of the Internet rather than from centralized systems. What does this mean for today's IT professional? In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will addresses this very serious issue of profound change in the industry.
Business as usual for IT is evolving into a "Make or Buy" decision on a service-by-service conversation with input from the LOBs. How does your organization move forward with cloud? In his general session at 16th Cloud Expo, Paul Maravei, Regional Sales Manager, Hybrid Cloud and Managed Services at Cisco, discusses how Cisco and its partners offer a market-leading portfolio and ecosystem of cloud infrastructure and application services that allow you to uniquely and securely combine cloud business applications and services across multiple cloud delivery models.
In his General Session at 16th Cloud Expo, David Shacochis, host of The Hybrid IT Files podcast and Vice President at CenturyLink, investigated three key trends of the “gigabit economy" though the story of a Fortune 500 communications company in transformation. Narrating how multi-modal hybrid IT, service automation, and agile delivery all intersect, he will cover the role of storytelling and empathy in achieving strategic alignment between the enterprise and its information technology.
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 peeled 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 fillin...
Growth hacking is common for startups to make unheard-of progress in building their business. Career Hacks can help Geek Girls and those who support them (yes, that's you too, Dad!) to excel in this typically male-dominated world. Get ready to learn the facts: Is there a bias against women in the tech / developer communities? Why are women 50% of the workforce, but hold only 24% of the STEM or IT positions? Some beginnings of what to do about it! In her Opening Keynote at 16th Cloud Expo, Sandy Carter, IBM General Manager Cloud Ecosystem and Developers, and a Social Business Evangelist, d...
Converging digital disruptions is creating a major sea change - Cisco calls this the Internet of Everything (IoE). IoE is the network connection of People, Process, Data and Things, fueled by Cloud, Mobile, Social, Analytics and Security, and it represents a $19Trillion value-at-stake over the next 10 years. In her keynote at @ThingsExpo, Manjula Talreja, VP of Cisco Consulting Services, discussed IoE and the enormous opportunities it provides to public and private firms alike. She will share what businesses must do to thrive in the IoE economy, citing examples from several industry sectors.
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discussed the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
SYS-CON Events announced today that the "Second Containers & Microservices Conference" will take place November 3-5, 2015, at the Santa Clara Convention Center, Santa Clara, CA, and the “Third Containers & Microservices Conference” will take place June 7-9, 2016, at Javits Center in New York City. Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities.
SYS-CON Events announced today that the "First Containers & Microservices Conference" will take place June 9-11, 2015, at the Javits Center in New York City. The “Second Containers & Microservices Conference” will take place November 3-5, 2015, at Santa Clara Convention Center, Santa Clara, CA. Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities.
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...
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 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal today!
In his keynote at 16th Cloud Expo, Rodney Rogers, CEO of Virtustream, discusses the evolution of the company from inception to its recent acquisition by EMC – including personal insights, lessons learned (and some WTF moments) along the way. Learn how Virtustream’s unique approach of combining the economics and elasticity of the consumer cloud model with proper performance, application automation and security into a platform became a breakout success with enterprise customers and a natural fit for the EMC Federation.
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.