[concurrency-interest] ThreadLocal vs ProcessorLocal

David M. Lloyd david.lloyd at redhat.com
Wed Oct 17 17:58:54 EDT 2012


Yes, the OS can and does move threads between CPUs.  The scarier 
question is: what do you do if/when a CPU is hot-plugged (i.e. 
enabled/disabled while the system is up)?

On 10/17/2012 04:30 PM, Dr Heinz M. Kabutz wrote:
> [newbie question]
>      Is it possible for a thread to ever be moved between processors, if
> for example the is an idle processor and another that is really busy? If
> not, then load balancing could be problematic.  If yes, then this means
> that we need to take this into consideration and not build static
> structures based on the value of which processor the thread is
> /currently/ running on.
>
> Again, if no, then what is the guarantee that it won't be available on
> some VMs or some hardware architectures or operating systems?
> [/newbie question]
>
> Regards
>
> Heinz
> --
> Dr Heinz M. Kabutz (PhD CompSci)
> Author of "The Java(tm) Specialists' Newsletter"
> Sun Java Champion
> IEEE Certified Software Development Professional
> http://www.javaspecialists.eu
> Tel: +30 69 75 595 262
> Skype: kabutz
>
>
>
> On 10/17/12 11:05 AM, Romain Colle wrote:
>> On Wed, Oct 17, 2012 at 9:15 AM, Kirk Pepperdine <kirk at kodewerk.com
>> <mailto:kirk at kodewerk.com>> wrote:
>>
>>     SOT, right now we are using CPUID for a number of reasons. Very
>>     easy to get to on Linux as we can do this in pure Java. However
>>     other platforms require C++/assembler so having <gulp> an unsafe
>>     operation in the JVM would be a win from my POV.
>>
>>
>> I strongly second that. It is next to impossible to implement most
>> NUMA-aware algorithms without knowing on which NUMA node the current
>> thread is running.
>> Having this information available as a Java class (in Thread, Unsafe,
>> ...) would be a huge win for people like us that need NUMA-aware behavior.
>>
>> Cheers,
>>
>> --
>> Romain Colle
>> R&D Project Manager
>> QuartetFS
>> 2 rue Jean Lantier, 75001 Paris, France
>> http://www.quartetfs.com <http://www.quartetfs.com/>
>> ------------------------------------------------------------------------
>>
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>
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- DML


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