Real-time Java: Difference between revisions

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{{more footnotes|date=June 2017}}

'''Real time Java''' is a catch-all term for a combination of technologies that allows programmers to write [[Computer program|program]]s that meet the demands of [[Real time]] [[systems]] in the [[Java (programming language)|Java programming language]].

{{primary sources|date=June 2017}}

'''Real -time Java''' is a catch-all term for a combination of technologies that allowsenables programmers to write [[Computercomputer program|program]]s that meet the demands of [[Realreal-time computing|real-time]] [[systems]] in the [[Java (programming language)|Java programming language]].

Java's sophisticated [[memory management]], native support for [[Threadthread (computer sciencecomputing)|threading]] and concurrency, [[type safety]], and relative simplicity have created a demand for its use in many domains. Unfortunately,Its severalcapabilities propertieshave preventbeen itenhanced fromto beingsupport directlyreal-time suitable for use in [[Real time]]computational systemsneeds:

* Real-time Java does not supportsupports a strict [[Preemptionpreemption (computing)|priority -based]] [[Threadthread (computer sciencecomputing)|threading]] model. Early suggestions that it support such a model were abandoned because they could not be implemented without native bindings on the target [[Microsoft Windows|Windows]] and [[Solaris Operating System|Solaris]] platforms.,

* Becausebecause Java threads do not support priorities, Java [[Locklock (softwarecomputer engineeringscience)|locking]] mechanisms do not support [[priority inversion]] avoidance techniques, such as [[priority inheritance]] or the [[priority ceiling protocol]]., and

* event handling.

The initial proposal<ref>{{Cite web| title=Issues in the Design and Implementation of Real-Time Java | url=https://www.cs.cornell.edu/courses/cs614/1999sp/papers/rtji.pdf | archive-url=https://web.archive.org/web/20170809011950/http://www.cs.cornell.edu/courses/cs614/1999sp/papers/rtji.pdf | archive-date=2017-08-09}}</ref> for an open standard for real-time Java was put forth by Kelvin Nilsen, then serving as a research faculty member at Iowa State University. A follow-on overview paper was published in the ''[[Communications of the ACM]]''.<ref>{{cite journal | url=https://dl.acm.org/doi/abs/10.1145/276609.276619 | doi=10.1145/276609.276619 | title=Adding real-time capabilities to Java | date=1998 | last1=Nilsen | first1=Kelvin | journal=Communications of the ACM | volume=41 | issue=6 | pages=49–56 }}</ref> The overwhelmingly positive response to these early proposals resulted in a series of meetings hosted by the National Institute of Standards and Technology in an effort to establish an open standard for real-time Java. NIST was ultimately told that they were not the appropriate body to establish standards related to the Java language, as Java was trademarked, and the technologies were owned by Sun Microsystems. Therefore, NIST ended their efforts with publication of consensus requirements.<ref>{{cite journal | url=https://www.itl.nist.gov/div897/ctg/real-time/rtj-final-draft.pdf | title=Information Technology Laboratory | journal=NIST | date=28 April 2015 }}</ref> that could be considered by future standardization efforts to be hosted by Sun Microsystems.

* Because Java threads do not support priorities, Java [[Lock (software engineering)|locking]] mechanisms do not support [[priority inversion]] avoidance techniques, such as [[priority inheritance]] or the [[priority ceiling protocol]].

To overcome these difficulties,When the [[Java Community Process|Java Community]] introducedwas aformed, the very first effort was the specification for real-time Java, JSR001. As of 2006, aA number of implementations of the resulting ''[[Real-time specification for Java|Real-Time Specification for Java]]'' (''RTSJ'') have emerged, including a [[Referencereference implementation (computing)|reference implementation]] from [[TimeSys|Timesys]], and[[IBM]]'s WebSphere Real Time, [[Sun Microsystems]]'s Java SE Real-Time Systems,<ref>{{Cite web|url=http://java.sun.com/javase/technologies/realtime/index.jsp|title=Sun Java Real-Time System|website=java.sun.com}}</ref> PTC Perc from [[PTC, Inc.]],<ref>{{Cite web|url=http://www.ptc.com/developer-tools/perc|title=Real-Time Java with PTC Perc &#124; PTC}}</ref> or [[JamaicaVM]] from aicas.

* More critically, the [[Garbage collection (computer science)|garbage collection]] behavior may introduce unbounded delays in [[computation]], immediately destroying any chance of making real-time guarantees for programs written in Java.

The RTSJ addressesaddressed the critical issues by mandating a minimum specification for the threading model (and allowing other models to be plugged into the VM) and by providing for areas of [[memory]] that are not subject to garbage collection, along with threads that are not preemptable by the garbage collector. These areas are instead managed using [[region-based memory management]]. The latest specification, 2.0, supports direct device access and deterministic garbage collection as well.

To overcome these difficulties, the [[Java Community Process|Java Community]] introduced a specification for real-time Java, JSR001. As of 2006, a number of implementations of the resulting ''[[Real-time specification for Java|Real-Time Specification for Java]]'' (RTSJ) have emerged, including a [[Reference implementation (computing)|reference implementation]] from [[Timesys]], and [[Sun Microsystems]]'s Java SE Real-Time System.

The RTSJ addresses the critical issues by mandating a minimum specification for the threading model (and allowing other models to be plugged into the VM) and by providing for areas of [[memory]] that are not subject to garbage collection, along with threads that are not preemptable by the garbage collector.

==Real-Time Specification for Java==

The ''Real-Time Specification for Java'' (RTSJ) is a set of [[Interface (computer science)|interface]]s and behavioral specificationsrefinements that allow forenable real-time [[computer programming]] in the [[Java (programming language)|Java programming language]]. RTSJ 1.0 was developed as JSR 1 under the [[Java Community Process]], which approved the new standard in November, 2001. [[As of 2006]], RTSJ 12.10 is being developed under JSR 282. A draft version is available at a JCP page.<ref>https://www.jcp.org/en/jsr/detail?id=282 JSR 282</ref> More information can be found from Aicas.<ref>{{Cite web | title=Real-Time Specification for Java {{!}} aicas.com | url=https://www.aicas.com/cms/rtsj | archive-url=https://web.archive.org/web/20150526085240/https://www.aicas.com/cms/rtsj | access-date=2025-02-17 | archive-date=2015-05-26}}</ref>

==See also==

* [[Javolution]] -– Real-TimeRTSJ Compliant Java Library ([[open-source]])

*[[Functional specification]]

==References==

*[[Javolution]] - RTSJ Compliant Java Library ([[open-source]])

{{Reflist}}

==External links==

* [https://www.cs.cornell.edu/courses/cs614/1999sp/papers/rtji.pdf Issues in the Design and Implementation of Real-Time Java]

* [https://dl.acm.org/doi/abs/10.1145/276609.276619 Adding Real-Time Capabilities to Java]

* [https://www.itl.nist.gov/div897/ctg/real-time/rtj-final-draft.pdf Requirements for Real-Time Extensions for the Java Platform]

* [http://aicas.com/cms/en/rtsj Real-Time Specification for Java 2.0 (RTSJ 2.0)]

* [http://jcp.org/en/jsr/detail?id=282 JSR-282]

* [http://www.rtsj.org/ Real-Time Specification for Java (RTSJ)]

* [http://jcp.org/en/jsr/detail?id=1 JSR-1]

* [https://web.archive.org/web/20090130041631/http://www-03.ibm.com/linux/realtime.html IBM WebSphere Real Time] a fully conformant RTSJ SE VM

* [http://www.aonix.com/ PERC] a real-time VM based on Java Standard Edition rather than RTSJ

* [http://www.aicas.com/jamaica.html JamaicaVM] {{Webarchive|url=https://web.archive.org/web/20120229051714/http://www.aicas.com/jamaica.html |date=2012-02-29 }} an RTSJ SE implementation with deterministic garbage collection

* [http://java.sun.com/javase/technologies/realtime.jsp Sun Java SE Real-Time System]

* [http://www.aonixptc.com/developer-tools/perc PTC PERCPerc] a real-time VM based on Java Standard Edition but with a patented deterministic garbage collection technology rather than RTSJ

* [http://javawww.sunoracle.com/technetwork/java/javase/technologiestech/realtime.index-jsp-139921.html Sun Java SE Real-Time System]

* [http://www.apogee.com/ Apogee real-time Java with real-time GC (discontinued)]

* [http://www.timesys.com/java/ Timesys RTSJ implementation and testing toolkit]

* [httphttps://jrate.sourceforge.net/ jRate (Java Real-Time Extension)] an open-source extension of the GNU GCJ compiler front-end and runtime system which adds support for most of the features required by the RTSJ.

* [http://www.cs.purdue.edu/homes/jv/JTRES05/index.html International Workshop on Java Technologies for Realtime and Embedded Systems (JTRES 2005)] {{Webarchive|url=https://web.archive.org/web/20130831081730/http://www.cs.purdue.edu/homes/jv/JTRES05/index.html |date=2013-08-31 }} [http://www-users.cs.york.ac.uk/~andy/JTRES06/ JTRES 2006] [http://www.vmars.tuwien.ac.at/jtres2007/ JTRES 2007] {{Webarchive|url=https://web.archive.org/web/20120206032740/http://www.vmars.tuwien.ac.at/jtres2007/ |date=2012-02-06 }} [http://jtres.java.sun.com/2008/ JTRES 2008] {{Webarchive|url=https://web.archive.org/web/20080628074409/http://jtres.java.sun.com/2008/ |date=2008-06-28 }} [http://pan.vmars.tuwien.ac.at/jtres2009/ JTRES 2009] {{Webarchive|url=https://web.archive.org/web/20150714214039/http://pan.vmars.tuwien.ac.at/jtres2009/ |date=2015-07-14 }} [http://d3s.mff.cuni.cz/conferences/jtres2010/ JTRES 2010] [http://www.artist-embedded.org/artist/JTRES-2011.html JTRES 2011] [http://jtres2013.atego.com/ JTRES 2012] {{Webarchive|url=https://web.archive.org/web/20131007110627/http://jtres2013.atego.com/ |date=2013-10-07 }} [http://jtres2013.atego.com/ JTRES 2013] {{Webarchive|url=https://web.archive.org/web/20131007110627/http://jtres2013.atego.com/ |date=2013-10-07 }} [http://jtres2014.compute.dtu.dk/ JTRES 2014] [http://jtres2015.univ-mlv.fr/ JTRES 2015]

* [http://www.aicas.com/ JamaicaVM] a Real-Time JVM

* [https://git.cs.lth.se/ljrt/ljrtcompiler LJRT Lund Java based Real-Time open source]

* [http://www.ddci.com/products_scorpion.php DDC-I Scorpion Java] real-time Java SE, with safety-critical and secure versions.

* {{usurped|1=[https://web.archive.org/web/20110106194536/http://www.ovmj.net/ Ovm]}}

* [http://www-users.cs.york.ac.uk/~andy/JTRES06/ International Workshop on Java Technologies for Real-time and Embedded Systems (JTRES 2006)] [http://www.vmars.tuwien.ac.at/jtres2007/ JTRES 2007] [http://jtres.java.sun.com/2008/ JTRES 2008]

* {{usurped|1=[https://web.archive.org/web/20090714105647/http://www.fiji-systems.com/ Fiji VM real-time Java ]}}

[[Category:Java programming language]]

* [https://rtjava.blogspot.com/2009/07/real-time-java-vms.html Real-time Java VMs ]

[[Category:Java (programming language)]]

[[Category:Real-time computing]]