root t returns the root of the store.

df t returns the percentage of free space in the store.

build t ~id fn runs fn tmpdir to add a new item to the store under key id. On success, tmpdir is saved as id, which can be used as the base for further builds, until it is expired from the cache. On failure, nothing is recorded and calling build again will make another attempt at building it. The builder will not request concurrent builds for the same id (it will handle that itself). It will also not ask for a build that already exists (i.e. for which result returns a path).

• parameter base

  Initialise tmpdir as a clone of base.

delete t id removes id from the store, if present.

result t id is the path of the build result for id, if present.

log_file t id is the path of the build logs for id. The file may not exist if the build has never been run, or failed.

state_dir is the path of a directory which can be used to store mutable state related to this store (e.g. an sqlite3 database).

cache ~user t name creates a writeable copy of the latest snapshot of the cache name. It returns the path of this fresh copy and a function which must be called to free it when done. If the cache name does not exist, it is first created (as an empty directory, and owned by user). When the copy is released, it is snapshotted to become the new latest version of the cache, unless the cache has already been updated since it was snapshotted, in which case this writeable copy is simply discarded.

delete_cache t name removes the cache name, if present. If the cache is currently in use, the store may instead return Error `Busy.

complete_deletes t attempts to wait for previously executed deletes to finish, so that the free space is accurate.