I’ve been trying to generate a OpenMP enabled precompiled header (PCH) with cppyy
and have been failing so far. Instead of doing so manually each time as outlined in this answer, I’m looking for an automated solution.
So far, the broad method is to use os.environ
to export environmental variables – but this seems to fail somewhat inconsistently, resulting in single-threaded code each time.
In particular, there doesn’t seem to be any output from cppyy_backend.loader.ensure_precompiled_header
all the time. Even if there is output, it has no effect on whether the C++ code runs parallely or not.
The relevant part of the code below:
import cppyy_backend.loader as l
os.environ['EXTRA_CLING_ARGS'] = '-fopenmp -O2 -g'
l.set_cling_compile_options(True)
current_folder = os.path.split(os.path.abspath(__file__))[0]
pch_folder = os.path.join(current_folder, 'cling_pch/')
if os.path.exists(pch_folder):
pass
else:
os.mkdir(pch_folder)
l.ensure_precompiled_header(pch_folder)
# find PCH file:
pch_path = glob.glob(pch_folder+'/allDict*')
if len(pch_path)>0:
os.environ['CLING_STANDARD_PCH'] = pch_path[0]
else:
raise ValueError('Unable to find a precompiled header...')
System specs:
- Ubuntu 18.04.2 LTS
- python 3.9.0
- cppyy 2.4.0
- cppyy_backend 6.27.0
EDIT:
I made sure the custom PCH folder was first empty while checking to see if the custom PCH file was being created.
2
Answers
I'm not sure about this, and will be able to confirm in a few days, but... I now suspect the reason there was an inconsistency in PCH creation was that
cppyy
was being called before theEXTRA_CLING_ARGS
were being set.I guess this means the 'standard' pre-compiled header was first being loaded and the 'custom' arguments were being ignored. During debugging or over the course of multiple runs - sometimes the effective order of execution was reversed.
If you set
CLING_STANDARD_PCH
to the desired name, it will be used as the name for the generated PCH. Conversely, if you set the folder name to the lower level call fromloader
, it will setCLING_STANDARD_PCH
for you. Setting both should not be necessary.The default naming scheme will generate a differently named PCH if OpenMP is enabled from when it’s not (a
.omp.
part is added to the name). This allows you to go back end forth, without bothering having to rebuild the PCH each time. Likely, you have multiple editions in thecling_pch
directory, andpch_path[0]
may well be a non-OpenMP variant.If you want to stay close to the above, though, then how about: