Introduction to the Real-Time Specification for Java
- Guiding Principles
- Overview of the Seven Enhanced Areas
This book is a preliminary release of The Real-Time Specification for Java (RTSJ). The final version will be available with the release of the reference implementation.
The Real-Time for Java Expert Group (RTJEG), convened under the Java Community Process and JSR-000001, has been given the responsibility of producing a specification for extending The Java Language Specification and The Java Virtual Machine Specification and of providing an Application Programming Interface that will enable the creation, verification, analysis, execution, and management of Java threads whose correctness conditions include timeliness constraints (also known as real-time threads). This introduction describes the guiding principles that the RTJEG created and used during our work, a description of the real-time Java requirements developed under the auspices of The National Institute for Standards and Technology (NIST), and a brief, high-level description of each of the seven areas we identified as requiring enhancements to accomplish our goal.
The guiding principles are high-level statements that delimit the scope of the work of the RTJEG and introduce compatibility requirements for The Real-Time Specification for Java.
Applicability to Particular Java Environments: The RTSJ shall not include specifications that restrict its use to particular Java environments, such as a particular version of the Java Development Kit, the Embedded Java Application Environment, or the Java 2 Platform, Micro Edition (J2ME).
Backward Compatibility: The RTSJ shall not prevent existing, properly written, non-real-time Java programs from executing on implementations of the RTSJ.
Write Once, Run Anywhere: The RTSJ should recognize the importance of "Write Once, Run Anywhere," but it should also recognize the difficulty of achieving WORA for real-time programs and not attempt to increase or maintain binary portability at the expense of predictability.
Current Practice vs. Advanced Features: The RTSJ should address current real-time system practice as well as allow future implementations to include advanced features.
Predictable Execution: The RTSJ shall hold predictable execution as first priority in all tradeoffs; this may sometimes be at the expense of typical general-purpose computing performance measures.
No Syntactic Extension: In order to facilitate the job of tool developers, and thus to increase the likelihood of timely implementations, the RTSJ shall not introduce new keywords or make other syntactic extensions to the Java language.
Allow Variation in Implementation Decisions: The RTJEG recognizes that implementations of the RTSJ may vary in a number of implementation decisions, such as the use of efficient or inefficient algorithms, tradeoffs between time and space efficiency, inclusion of scheduling algorithms not required in the minimum implementation, and variation in code path length for the execution of byte codes. The RTSJ should not mandate algorithms or specific time constants for such, but require that the semantics of the implementation be met. The RTSJ offers implementers the flexibility to create implementations suited to meet the requirements of their customers.