libopenblas is a fairly low-level library, and can get pulled in transitively

via dependencies. e.g., [tgen](https://github.com/shadow/tgen) uses libigraph,

which links against liblapack, which links against blas.

libopenblas, when compiled with pthread support, makes extensive use of

spin-waiting in `sched_yield`-loops, which currently result in deadlock under

Shadow.

There are several known workarounds:

* Use a different implementation of libblas. e.g. on Ubuntu, there are several

alternative packages that can [provide

libblas](https://packages.ubuntu.com/hirsute/libblas.so.3). In particular,

[libblas3](https://packages.ubuntu.com/hirsute/libblas3) doesn't have this issue.

* Install libopenblas compiled without pthread support. e.g. on Ubuntu this can

be obtained by installing

[libopenblas0-serial](https://packages.ubuntu.com/hirsute/libopenblas0-serial)

instead of

[libopenblas0-pthread](https://packages.ubuntu.com/hirsute/libopenblas0-pthread).

* Configure libopenblas to not use threads at runtime. This can be done by

setting the environment variable `OPENBLAS_NUM_THREADS=1`, in the process's

[environment](https://shadow.github.io/docs/guide/shadow_config_spec.html#hostshostnameprocessesenvironment)

attribute in the Shadow config.

See also:

* [libopenblas deadlocks](https://github.com/shadow/shadow/issues/1788)

* [sched\_yield loops](https://github.com/shadow/shadow/issues/1792)