topic Re: Re:Code stops after a call to BLACS_GRIDEXIT in Intel® oneAPI Math Kernel Library

Code stops after a call to BLACS_GRIDEXIT

OP1 — Fri, 26 Sep 2025 20:59:14 GMT

The following code (built with ifx 2025.2.1 on Windows and run with 7 processes) silently crashes after the call to BLACS_GRIDEXIT on line 19 (namely, it does not execute anything past line 19).

The code is linked with the ilp64 MKL libraries for BLACS and ScaLAPACK.

Am i missing something obvious here?

PROGRAM TEST IMPLICIT NONE (TYPE, EXTERNAL) EXTERNAL BLACS_GRIDINIT, BLACS_GRIDINFO, BLACS_PINFO, BLACS_GET, BLACS_PCOORD, BLACS_GRIDEXIT INTEGER(KIND = 8), EXTERNAL :: BLACS_PNUM INTEGER(KIND = 8) :: ICTXT, MY_ID, N_PROCS, N_PROW, N_PCOL INTEGER(KIND = 8) :: MY_ROW, MY_COL CALL BLACS_PINFO(MY_ID, N_PROCS) N_PROW = INT(SQRT(REAL(N_PROCS))) N_PCOL = N_PROCS/N_PROW CALL BLACS_GET(-1_8, 0_8, ICTXT) CALL BLACS_GRIDINIT(ICTXT, 'C', N_PROW, N_PCOL) CALL BLACS_GRIDINFO(ICTXT, N_PROW, N_PCOL, MY_ROW, MY_COL) IF (MY_ID /= 6) THEN WRITE(*, *) 'C', MY_ID, BLACS_PNUM(ICTXT, MY_ROW, MY_COL), MY_ROW, MY_COL END IF CALL BLACS_GRIDEXIT(ICTXT) CALL BLACS_GET(-1_8, 0_8, ICTXT) CALL BLACS_GRIDINIT(ICTXT, 'R', N_PROW, N_PCOL) CALL BLACS_GRIDINFO(ICTXT, N_PROW, N_PCOL, MY_ROW, MY_COL) IF (MY_ID /= 6) THEN WRITE(*, *) 'R', MY_ID, BLACS_PNUM(ICTXT, MY_ROW, MY_COL), MY_ROW, MY_COL CALL BLACS_GRIDEXIT(ICTXT) END IF END PROGRAM TEST

Re: Code stops after a call to BLACS_GRIDEXIT

OP1 — Fri, 26 Sep 2025 21:01:11 GMT

Line 26 in the code above should be removed (i should have done so before posting...) but this does not modify the outcome here.

Re: Code stops after a call to BLACS_GRIDEXIT

OP1 — Fri, 26 Sep 2025 21:03:28 GMT

Also, when did we lose the ability to edit posts?

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Wed, 01 Oct 2025 14:44:42 GMT

Hi,

Does the same problem happen when running for 6 or 8 processes?

You create a grid of size 2×3 (6 positions), but you're running with 7 processes. Process number 6 has no valid grid position, which can cause the MPI to abort.

Regards,

Alex

Re: Re:Code stops after a call to BLACS_GRIDEXIT

OP1 — Wed, 01 Oct 2025 15:29:57 GMT

I am afraid that I do not understand your reply at all. Are you saying that it is impossible to run an arbitrary number of processes for a program relying on BLACS, and that only the number of processes that match exactly the number of processes in a BLACS process grid is allowed? This is not how BLACS work!

I simplified the code a bit further:

PROGRAM TEST IMPLICIT NONE (TYPE, EXTERNAL) EXTERNAL BLACS_GRIDINIT, BLACS_PINFO, BLACS_GET, BLACS_GRIDEXIT INTEGER(KIND = 8) :: ICTXT, MY_ID, N_PROCS, N_PROW, N_PCOL CALL BLACS_PINFO(MY_ID, N_PROCS) N_PROW = INT(SQRT(REAL(N_PROCS))) N_PCOL = N_PROCS/N_PROW CALL BLACS_GET(-1_8, 0_8, ICTXT) CALL BLACS_GRIDINIT(ICTXT, 'C', N_PROW, N_PCOL) CALL BLACS_GRIDEXIT(ICTXT) WRITE(*, *) MY_ID END PROGRAM TEST

Running the code with 7 processes, the output is:

1 0 3 5 2 4 Press any key to continue . . .

Why isn't process 7 printing anything here?

Re: Re:Code stops after a call to BLACS_GRIDEXIT

OP1 — Wed, 01 Oct 2025 15:36:04 GMT

[ignoring the fact that I should have written "process 6" in my latest message]

In fact, when I run this simplified example consecutively, multiple times, sometimes I get no output at all, sometimes only a subset of the processes 0... 5 print something. There is a randomness to it. Can you try to repeat this on your side?

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Wed, 01 Oct 2025 16:06:07 GMT

Could you share how exactly you are running the code? So that I could precisely reproduce your issue.

Re: Re:Code stops after a call to BLACS_GRIDEXIT

OP1 — Wed, 01 Oct 2025 17:12:03 GMT

Here is the BuildLog.htm file that is produced when building the last example above.

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Fri, 17 Oct 2025 13:58:13 GMT

Hi,

We investigated your issue and confirmed that the problem is in the gridexit call. The context of rank 6 is set to -1 during blacs_gridinit -> blacs_gridmap, which causes the error when gridexit is called. You were right that it is fine to use only a subset of processes for computation. Nevertheless, it is not a bug, as this behavior of gridexit is consistent with the reference BLACS implementation (SCALAPACK: blacs_gridexit_).

Regards,

Alex

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Tue, 21 Oct 2025 11:29:39 GMT

Hi,

Do you have any further questions on the topic?

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Fri, 24 Oct 2025 08:27:02 GMT

Hi,

I hope that you found the above explanation useful. We'll monitor this thread for another 3 days for any follow-up questions. If there's no response within that time, this thread will no longer be actively supported by Intel.

Regards,

Alex

Re:Code stops after a call to BLACS_GRIDEXIT

Aleksandra_K — Fri, 31 Oct 2025 12:32:53 GMT

With no response from you, this issue will no longer be tracked by Intel. If you need any additional information, please post a new question, ideally in a new thread,

Regards,

Alex