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1 Reply Latest reply: Jan 16, 2008 5:47 PM by 807557 RSS

Questions concerning RTJ 2.x

807557 Newbie
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- Does/Will JRT support 64 bit JVM? Is this on a Roadmap? And if so,
when? Along with this, what is the roadmap for support for Java 6 and 7?

- One of our Customers saw a Heap Limit for 32bit JVM that seems to be
at approx 3.5GB. Can this be confirmed?


- If there are 3rd party libraries already in use on the NON-RT JVM,
will these be affected under JRT? And if so with minimal to no code
changes?

- What guarantee/support can Sun give for Linux Kernel patch to
Linux(specifically Red Hat)What Kernel versions are supported? Who gives
Support? and under what SLA?

- What is meant in by "Carrier Grade" Linux?
  • 1. Re: Questions concerning RTJ 2.x
    807557 Newbie
    Currently Being Moderated
    BenP wrote:
    - Does/Will JRT support 64 bit JVM? Is this on a Roadmap? And if so,
    when? Along with this, what is the roadmap for support for Java 6 and 7?
    I'm not aware of any announced plans for either 64-bit support or Java 6/7 support. Perhaps one of our marketing folk can give more details.
    - One of our Customers saw a Heap Limit for 32bit JVM that seems to be
    at approx 3.5GB. Can this be confirmed?
    On a 32-bit VM a 3.5GB heap is the absolute best you can hope for and then only on certain operating systems and under the right conditions. A 2GB heap limit is imposed by some operating systems, but that doesn't mean the VM will be able to allocate a heap that size, as it (Hotspot) requires a contiguous memory space. I'm not aware of anything specific in Java RTS that would change this, but I'm sure one of our GC experts will correct me if needed.
    - If there are 3rd party libraries already in use on the NON-RT JVM,
    will these be affected under JRT? And if so with minimal to no code
    changes?
    Any existing Java 5 code will execute on the real-time VM in a non-realtime context. To answer how existing libraries will behave in a real-time context depends on the library (what it does and how it does it) and the actual real-time context. Many libraries cause problems if used from different memory contexts, but many work fine if always used from the same memory contexts - it all depends. You can't take arbitrary Java code and expect it to work out-of-the-box in either no-heap contexts, or from ScopedMemory.
    - What guarantee/support can Sun give for Linux Kernel patch to
    Linux(specifically Red Hat)What Kernel versions are supported? Who gives
    Support? and under what SLA?
    Sun can't guarantee anything about any Linux kernel patches. Java RTS requires the services of a real-time operating system to achieve its determinsim goals. If the underlying OS has problems in this area then you are advised to use one that is suitable for the job.

    Our early access 2.1 release for Linux (available very shortly) has been tested on two systems:

    - SUSE Linux Enterprise Real Time 10 (released) http://www.novell.com/products/realtime/
    - Red Hat Enterprise MRG 1.0 (to be released) http://www.redhat.com/mrg/?intcmp=70160000000HEmC

    We do not claim to have achieved our determinism goals on these platforms as yet - that is still work in progress as we head to the 2.1 release.

    In general we suggest installing a 2.6.21 Linux kernel or later with the RT patch maintained by Ingo Molnar and a 2.5 glibc or later.

    I can't comment on the SLA - you need to contact someone in the support channels. From my perspective as an engineer if we can reproduce a problem on our supported platforms then we will investigate it further - as we do for any supported platform in the JDK. If it turns out to be a problem in the kernel then we'll try to work-around it if feasible and raise a bug for it (as we already have).
    - What is meant in by "Carrier Grade" Linux?
    It is a Linux distribution that meets a set of additional specifications, regarding availability, scalability, quality-of-service, that make it suitable for use in the telecommunications field.

    http://en.wikipedia.org/wiki/Carrier_Grade_Linux

    Hope this help.

    David Holmes