I have no idea about your question. You can either contact technical support or set up a test of your own where the assignment takes long enough that you can test if it gets interrupted. Also, you should probably make this an enhancement request – please see the support link on the right of this blog.

–Loren

here is a good question on MATLAB timers:
Suppose I want to update several variables (say a and b) “atomically” in MATLAB (for the purposes of multiple timers).

Would [a,b] = deal(…,…); do the job, or can the assignment be interrupted by a timer? If it is safe in current versions (which seems very likely to me), it is probably a good idea to retain this behavior for future MATLABs (potentially as valuable as having a compare-and-swap instruction in a processor).

Thanks,
Christian

Multithreading features change in MATLAB each release recently. I suggest reading release notes and contacting technical support (link at right) for the best information for your installation and configuration.

–Loren

I second Tom Crocket’s comment.

Inside a matlab script (batch mode) I tried

LASTNT=maxNumCompThreads(NTHREADS)

with several values for NTHREADS (1,4,8, etc)
on a 8-core 64bit Linux machine.
However, “top” shows all 8 cores working at ~100%,
regardless of the value I use for NTHREADS.

I tried also with Matlab interactively,
but I get the same 8 cores working, no matter what I do.

(Matlab R2009a_64bit, Linux, CentOS 5.2)

Is there a way to limit the number of cores in use?
That would be very important and useful for multi-user
systems.

Thank you,
Gus Correa

You can set maxNumCompThreads(1); in toolbox/local/matlabrc.m, thus overwriting any user setting.
You can do this in 2 ways:

a) add the line before the section where user preferences are checked. In this way the preferences of the users are still repected, but the internal default behavior is overwritten.

b) add the line after the section. In this way you overwrite both the user settings and the internal setting, and you force your users to activate multi-threading explicitly in every session. That’s how we do it here.

The new default, i.e. automatic multi-threading, plus the problem with the Java garbage collector threads (1 per core) can turn Matlab into a DoS tool on our big SMPs, with 96-144 cores!

-Bernd

There is no such control over multithreading.

–Loren

Is there some way to change the multithreading default at a system-wide level from “automatic” to “manual” so that we (the system administrators) can keep the aggregate thread count to something manageable?

For a start, MATLAB wasn’t using multi-threaded BLAS in version 5.3. That has come much more recently.

You probably should contact technical support as your issue warrants more attention than I can give it here.

–Loren

Thanks,
Uvernes

You still haven’t shown code that we could look at. Please send a sample to technical support with information on the runs on different computers so they can dive into this with more information.

–Loren