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

Java's sophisticated [[Memory management|memory management]], native support for [[Thread (computing)|threading]] and concurrency, [[Type safety|type safety]], and relative simplicity have created a demand for its use in many domains.  Its capabilities have been enhanced to support real-time computational needs:

* Real-time Java supports a strict [[Preemption (computing)|priority-based]] [[Thread (computing)|threading]] model,
* because Java threads support priorities, Java [[Lock (computer science)|locking]] mechanisms support [[Priority inversion|priority inversion]] avoidance techniques, such as [[Priority inheritance|priority inheritance]] or the [[Priority ceiling protocol|priority ceiling protocol]], and
* event handling.

The initial proposal<ref>http://www.cs.cornell.edu/courses/cs614/1999sp/papers/rtji.pdf</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>https://dl.acm.org/doi/abs/10.1145/276609.276619</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>https://www.itl.nist.gov/div897/ctg/real-time/rtj-final-draft.pdf</ref> that could be considered by future standardization efforts to be hosted by Sun Microsystems.

When the [[Java Community Process|Java Community]] was formed, the very first effort was the specification for real-time Java, JSR001. A number of implementations of the resulting ''Real-time specification for Java'' (''RTSJ'') have emerged, including a reference implementation from [[Company:TimeSys|Timesys]], [[Company:IBM|IBM]]'s WebSphere Real Time, [[Company:Sun Microsystems|Sun Microsystems]]'s Java SE Real-Time Systems,<ref>[http://java.sun.com/javase/technologies/realtime/index.jsp Java SE Real-Time Systems]</ref> PTC Perc from PTC, Inc.,<ref>[http://www.ptc.com/developer-tools/perc PTC Perc]</ref> or [[JamaicaVM]] from aicas.

The RTSJ addressed 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|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|region-based memory management]].  The latest specification, 2.0, supports direct device access and deterministic garbage collection as well.

==Real-Time Specification for Java==
The ''Real-Time Specification for Java'' (RTSJ) is a set of interfaces and behavioral refinements that enable real-time [[Computer programming|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.  RTSJ 2.0 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>https://www.aicas.com/cms/rtsj</ref>

==See also==
* [[Software:Javolution|Javolution]] – RTSJ Compliant Java Library

==References==
{{Reflist}}

==External links==
* [http://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]
* [http://www-03.ibm.com/linux/realtime.html IBM WebSphere Real Time] a fully conformant RTSJ SE VM
* [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://www.ptc.com/developer-tools/perc PTC Perc] a real-time VM based on Java Standard Edition but with a patented deterministic garbage collection technology rather than RTSJ
* [http://www.oracle.com/technetwork/java/javase/tech/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]
* [http://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)] [http://www-users.cs.york.ac.uk/~andy/JTRES06/ JTRES 2006] [http://www.vmars.tuwien.ac.at/jtres2007/ JTRES 2007] [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] [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] [http://jtres2013.atego.com/ JTRES 2013] [http://jtres2014.compute.dtu.dk/ JTRES 2014] [http://jtres2015.univ-mlv.fr/ JTRES 2015]
* [https://git.cs.lth.se/ljrt/ljrtcompiler LJRT Lund Java based Real-Time open source]
* [http://www.ovmj.net/ Ovm]
* [http://www.fiji-systems.com/ Fiji VM real-time Java ]
* [http://rtjava.blogspot.com/2009/07/real-time-java-vms.html Real-time Java VMs ]

[[Category:Java (programming language)]]
[[Category:Real-time computing]]

{{Sourceattribution|Real-time Java}}