GNU OpenMP forbids xr.align

[j-haacker]

Describe the bug
Processing L1b data in parallel fails. The reasons seems to be that GNU OpenMP does not allow xarray to fork processes within a forked worker.

To Reproduce
Steps to reproduce the behavior:
Run l2.from_id(list, cores=2) with list containing multiple track IDs per month.

Error message
Terminating: fork() called from a process already using GNU OpenMP, this is unsafe.

Environment
Linux kernel 5.15

[j-haacker]

Work-around

Two work-arounds worked for me:

1. If you have access to a compute node, try do the processing there. The compute node may use a different message passing interface (MPI).
2. Pass cores=1 to disable parallel processing. You can still manually start multiple process, e.g., to compute different periods each. In that case and if you will continue gridding the data, make use of kwarg cache_fullname to specify different cache names for each job. You can later merge the cache files using misc.merge_l2_cache.