Want your Java fast or predictable ? Java RTS 2.1 is here
When you leave work, would you rather it be likely that you get home really quickly, or would you rather be sure you will get home by a certain time ?
If you send a birthday card, would you rather they try to get it there as soon as possible, or just know it will definitely get there on the day ?
If you order something for yourself on Amazon, do you pick the cheapest delivery option because most of the time it gets there 2 days after it ships even though it doesn’t say so ?
Fast, and Better Late than Never, but…
For many years, we have focussed in Java SE on making the runtime fast. Fast in a number of ways: fast to render graphics (in particular, in the upcoming 6u10 release), fast to execute server applications, fast to start up, for example. And if you follow Dave Dagastine’s blog you will know that we frequently hold the gold medal for various of the races laid out by the SPEC.
But one thing the HotSpot JVM is not tuned for is hard predictability. That is to say, there is no guarantee that a certain task will take no longer than a certain amount of time. The native OS may choose to schedule something ahead of the JVM process supporting your application. Classloading or performance optimizations such as just-in-time compilations may put your application thread in the backseat. Or, probably most recognizable to users of your application, a garbage collection may kick in when you least expect it. Such non-deterministic behavior is just fine for many applications. Moreover, it allows the JVM to tune for big picture performance characteristics, like overall throughput averaged over a complete run of your application, even if one or two of your application tasks unexpectedly end up taking longer than you thought. The needs of the many outweighing the needs of the few, in Vulcan.
But anyone who has been late picking up a small child from daycare will know that there are some tasks that just have to get done within a certain time period. Even if it’s at the expense of completing others you thought you might have time for.
…sometimes, Best is Never Late
So for nearly as many years as we have had been tuning performance in the JDK, Greg has been leading our real-time variant of Java SE, called the Java Real Time System (Java RTS). This implementation is at the other end of the predictability versus speed continuum, where your application may select tasks (zero to all of them) as tasks that must complete within a given time period. There is no ‘better late than never’ here: late equals failure for this implementation of Java SE.
Java RTS 2.1 is Released !
And Java RTS recently hit a new milestone with a significant upgrade to version 2.1, which you can check out here.
The main elements of Java RTS over the usual Java SE you are probably more familiar with are:-
- the javax.realtime.* APIs
In addition to the regular Java SE APIs, these APIs allow you to code
parts of your application with the real-time guarantees it needs. This
means Java RTS runs regular Java SE applications, but provides no
realtime guarantees to any of the tasks in the application unless you
adapt the application to use the javax.realtime APIs to ask for those
- a VM tuned for realtime behavior
For example, containing a garbage collector that runs at a lower
priority than real time application threads so as not to delay them.
- Bindings to the realtime aspects of the underlying OS
The realtime system is only as good as the underlying OS can guarantee
(which is why we only offer it on Solaris and some Linux
distributions). These bindings, for example, ensure that JVM threads
are properly scheduled by the OS scheduler.
Our own Paul Hohensee and Brian Goetz have been writing in detail about both the additional programming APIs and the implementation, here and here.
We’ve got folks using the Java RTS in traditional settings like industrial automation projects, an of course in robots - where the multiple processing involved in moving a complex limb have to be coordinated, even at JavaOne.. But more recently we have a lot of interest in the financial world from folks writing trading applications, where certain timing guarantees need to be met.
In a world where even driving in a circle can get crazy, its good to know you can choose Predictable if you need it.
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