WebSphere Real Time

Traditional real-time systems require significant application programming skills. Typically, the marketplace has relied on application programming languages such as ADA, C, and C++. Skills in these languages are becoming scarce and in great demand. Further, applications written in these languages are difficult to port from one platform to another. In contrast, applications written in the Java programming language are relatively easy to port to other vendors' platforms and programming skills are readily available. However, commercial Java Runtime Environments (JRE) are not able to deliver real-time behavior because of the unpredictability of application execution time. Two areas that can give rise to such unpredictability are:

WebSphere Real Time V3.0 is a Java Runtime Environment and development kit designed to provide more consistent performance for Java applications, enabling customers to develop applications with low latency and highly predictable response times. WebSphere Real Time V3.0 can be used in servers or other Java applications that want to deliver consistent performance and service quality (soft real-time for Linux and for IBM AIX) and it can also be used to build real-time Java systems that can meet aggressive and stringent timing constraints (hard real-time for real-time Linux).

The key advantage to WebSphere Real Time is that it is designed to reduce or eliminate the primary source of unpredictable application pauses via its “Metronome” Garbage Collection technology while preserving the benefits of using the Java language.

When using WebSphere Real Time, typical applications can expect average garbage collection pauses less than 1ms on Red Hat MRG / Novell SLERT real-time operating systems and configurable pause time target (1ms and up) on other supported operating systems, defaulting to under 3ms. By preserving the garbage collection model, memory management remains transparent to developers, unlike an alternative approach called "scoped memory." Scoped memory can be extremely difficult to use, introducing complexities in programming and forcing developers to determine their memory requirements prior to runtime. Further, by utilizing existing Java class libraries, WebSphere Real Time retains the productivity and reusability aspects that make Java so attractive.

WebSphere Real Time reduces the problem with class loading through the use of the shared class cache to store classes in an internal format close to that used by its virtual machine at runtime. Ahead-of-time (AOT) and just-in-time (JIT) compilation can be further used to optimize the execution environment. In particular, AOT code can be stored into a shared class cache before program runtime and can be loaded into the virtual machine as classes are loaded, to provide the highest level of deterministic performance. The JIT compiler runs asynchronously on a low-priority thread so that it can dynamically improve the performance of an application while giving system designers a simple way to prevent the compiler from interfering with higher-priority application tasks.

For applications that require even lower latency than provided by the real-time garbage collection, WebSphere Real Time supports the Real Time specification for Java (RTSJ). Programmers can use the many standard features, including priority-based thread scheduling, high-resolution timers, and asynchronous event handlers.

The RTSJ, also known as Java Specification Request 1 (JSR-1), extends the Java language to support real-time behavior. It defines a number of language constructs similar to the traditional real-time programming languages. In doing so, it extends the Java programming model by allowing the application programmer to control memory areas ("Scoped Memory"), thread scheduling, and asynchronous event handling. While features such as scoped memory are incredibly powerful, and are required for applications that require sub-millisecond worst-case delays, they require much more significant programming skills, in particular for managing memory. WebSphere Real Time enables customers to write the majority of their application using standard Java, dipping into the powerful constructs in RTSJ as required. For many applications, features such as scoped memory will not be required, but the other features of RTSJ are fully available.

WebSphere Real Time is comprised of the following components:

WebSphere Real Time is supported on IBM hardware that has firmware compatible with real-time requirements. The firmware has been designed to eliminate system management events that may interrupt the processing of real-time applications and result in nondeterministic behavior.

A core feature of the real-time environment is the underlying open source real-time operating system. WebSphere Real Time supports an enhanced Linux kernel using system libraries and binaries available from Red Hat and Novell. IBM worked with the Linux community to develop the real-time operating system capabilities needed to obtain required performance for WebSphere Real Time and has subsequently made them available via the open source community.

Software prerequisites:

WebSphere Real Time is supported on the following though without the benefit of the RTSJ support.

Certified hardware:

WebSphere Real Time for Linux is certified on multiprocessor variants of the following systems:

WebSphere Real Time for Linux is supported on hardware that runs a supported operating system, and that has these characteristics:

WebSphere Real Time for AIX is certified on multiprocessor variants of Common Hardware Reference Platform (chrp) systems. A system is a CHRP system if the command:
            lscfg -p | fgrep Architectures
replies with:
            Model Architecture: chrp