KSE, libpthread & libthr: almost newbie question

[Greg Lewis]

On Sun, Oct 29, 2006 at 09:05:11AM +0000, Robert Watson wrote:
> On Sat, 28 Oct 2006, Julian Elischer wrote:
> >Robert Watson wrote:
> >>On Fri, 27 Oct 2006, Julian Elischer wrote:
> >>
> >>>there is class of problems (e.g. some java programs) that have THOUSANDS 
> >>>of threads, each representing an active aspect of some object. How do 
> >>>you put an rlimit on that without either 1/ stopping the program from 
> >>>working or 2/ allowing thousands of threads to exist but not screwing 
> >>>other users.
> >>
> >>Does the JVM actually expose thousands of threads to the OS, or does it 
> >>actually do its own M:N threading internally based on its execution 
> >>model? My impression is the latter, exposing threads to the OS only when 
> >>it needs them to consume kernel or CPU resources.
> >
> >I don't know the answer to that question, only that there is a class of 
> >program style that uses this model.
> 
> FYI, last night following comments about the change away "green threads", I 
> ran some simple tests with the 1.4.2 JVM.  It appears that, at least in my 
> simple test cases, all threads created in the JVM are exposed to the OS. 
> Typically this appears to be about n+8 to n+9 threads, where n is the 
> number of threads created by the application itself, and 8/9 is the number 
> created by the JVM.  I assume the variance of one is likely the garbage 
> collector kicking in every now and then (or something along those lines).

If you really want to know, just send the running process a SIGQUIT and
it will dump the currently running threads to stdout.  But yes, 1.4 and 1.5
both use "native" threads which correspond 1:1 with OS threads (plus
there are threads the JVM creates itself, as you note).  The JVM threads
include garbage collection and AWT event handlers at least.

-- 
Greg Lewis                          Email   : glewis at eyesbeyond.com
Eyes Beyond                         Web     : http://www.eyesbeyond.com
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