Darius Buntinas wrote:

On Sep 22, 2010, at 12:04 PM, Terry Dontje wrote:

...

Darius Buntinas wrote: Ok I need a clarification here because I feel that I might be misinterpreting something. So is the CANNOT_CONTINUE error class only returned by MPI after a previous error condition has been returned that has caused problems? For example let's say we did an MPI_Bcast that resulted in a return of MPI_ERR_OP and for whatever reason the MPI library is borked. So the next call to MPI would return the CANNOT_CONTINUE error class?

Yes, I believe that's the behavior we talked about at the forum.

...

So is this an escape hatch for an implementation that does not support any type of fault tolerance to explicitly notify the user they shouldn't proceed any further? I really wonder how many implementations will do such.

Well, I wouldn't say it's an escape hatch, since an implementation that doesn't support any fault tolerance needn't ever return CANNOT_CONTINUE. Because we still haven't defined what happens after an error, operation after an error is still undefined, the implementation is still free to do anything including returning MPI_SUCCESS.

However, a high quality implementation, would return CANNOT_CONTINUE on subsequent MPI calls when it knows that something is borked beyond repair.

Note that there's still a lot of middle ground between "no errors" and "totally borked". We're giving the implementation an error to return if it finds itself totally borked. This is why I agree with Josh's statement that this proposal is a minor change.

That's funny, because I was thinking a high quality implementation would never return CANNOT_CONTINUE but more distinct error codes that lets an application to recover. I would think very few errors would actually completely obliterate an MPI library's internal structures. At least the implementations I've seen that's seems to be the case. --td

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