std

currently holds both lightweight async helpers and heavier concurrency primitives. As the latter group grows, the module name stops describing its contents well. The concurrency items are categorically different from the rest of the module, they should get their own package. The concurrency module is about coordinating shared access to resources. This mirrors the and split that was done. The split is clean: , (in the works), , and have no internal dependencies on other files. These are low-level synchronisation primitives. All four are still unstable, so there should be no deprecation overhead. "Concurrency primitives" is a well-understood category, and it gives the new package a natural growth path (e.g. , , ...) without further bloating . I renamed the files, since the new module itself is unstable.