[Beowulf] MPICH2: Handle Limit?

R Hamann rhamann at uccs.edu
Fri Feb 4 11:31:01 PST 2005


I thought any limit would be wierd, let alone something like 84 (7 X 
12?)  Anyway, I thought it was based on the number of MPI variables 
declared (data_types, windows, requests) because every time I added 
new declarations, it would hang on Fedora core 2, but run to 
completion on Scyld (but with erroneous results). If I deleted unused 
MPI declarations, it would start to work again.  I counted all my 
handles and came up with 84.

However, after deleting two 26 element arrays of handles, I thought it 
would work.  When I added more handles, it bombed again.  I started to 
try other things.  I added 4 junk ints.  I didn't use the variables I 
declared, but it still bombed.  When I converted them to chars, it 
started working again.  Very strange.

Have you ever encountered this before?   I'm doing a 3d cellular 
automata, so I need a lot of datatypes for exchange of ghost cells. 
 It's obviously some strange error I've made that's manifesting itself 
in MPI instead of a runtime or sytax error.  I'm gonna try looking for 
any buffer overruns now, but other than that I'm stumped.

GCC on Fedora Core 2 and on Scyld Beowulf
MPICH 2 1.0



On Fri, 4 Feb 2005 12:16:17 -0600 (CST)
  Rob Ross <rross at mcs.anl.gov> wrote:
> Hi Ron,
> There should not be an 84 handle limit.
> Can you tell me what version of MPICH2 this is, and what 
>architecture and 
> OS you're running on?  Do you have a simple test that exhibits the 
> problem?
> Thanks,
> Rob
> ---
> Rob Ross, Mathematics and Computer Science Division, Argonne 
>National Lab
> On Thu, 3 Feb 2005, R Hamann wrote:
>> I've been having some strange problems with a program using the 
>> library.  When I added some new datatypes for ghost cell exchange, 
>> program would hang.  I figured out that any number of handles over 
>> would cause this.  Fortunately, I could delete some handles that I 
>> longer needed, but it still seemed strange.  Are my calculations 
>> correct that for each process there is an 84 handle limit? or am I 
>> seeing some other problem?
>> Ron

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