Add openmp to the XFEL builder by default #1063

phyy-nx · 2025-04-16T17:19:05Z

This is the end of a rabbit hole of dependencies. I thought I'd write it here in case it comes up again. Thanks @fredericpoitevin and @nksauter.

psana is being upgraded to psana2, which can read xtc2, the file format created by lcls2
We found that the order of imports would cause a failure in a minimal script which connected to a psana2 data source. This would fail:

import rstbx.cftbx
import psana

But this would pass

import psana
import rstbx.cftbx

The problem was that cftbx triggers an import of rstbx/__init__.py which includes omptbx_ext, the OpenMP adapter in cctbx. At this point we think we know what happens next.
omptbx/omp_or_stubs.h includes this code:

#if defined(_OPENMP)
# define OMPTBX_HAVE_OMP_H
# include <omp.h>
#else
# define OMPTBX_HAVE_STUBS_H
# include <omptbx/stubs.h>
#endif

In other words, if OpenMP is enabled, use omp.h, otherwise stub out the OpenMP API. Since the new psana2 included a library which uses OpenMP (we think), these stubs would clobber psana.

Since we can't easily swap import orders around in the larger codebase, instead making --enable_openmp_if_possible=True the default for the XFEL builder is the best work around. That's already the case for the Phaser and Phenix builders so its not such a big step.

JBlaschke · 2025-04-18T16:51:20Z

I approve! See Gchat

Add openmp to the XFEL builder by default

de1e121

phyy-nx merged commit 2c38db9 into master Apr 18, 2025
101 checks passed

phyy-nx deleted the xfel_openmp branch April 18, 2025 16:59

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Add openmp to the XFEL builder by default #1063

Add openmp to the XFEL builder by default #1063

Add openmp to the XFEL builder by default #1063

Add openmp to the XFEL builder by default #1063

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