# Using igraph in multi-threaded programs

The igraph library is considered thread-safe on platforms that support thread-local storage. This currently includes Linux and MS Windows operating systems, but not Mac OSX. The best way to check whether an igraph build is thread-safe is checking the `IGRAPH_THREAD_SAFE` macro.

## Thread-safe ARPACK library

Note that igraph is only thread-safe if it was built with the internal ARPACK library, i.e. the one that comes with igraph. The standard ARPACK library is not thread-safe.