Function note_wanted 

fn note_wanted(
    sharing: &Sharing<'_>,
    memory: &Memory,
    missing: &BTreeMap<String, (String, u64)>,
    there: &BTreeSet<String>,
    now_ms: i64,
)

The sealed files this device waits for, said for the pull to fetch (blobs::Wanted, remote::fetch_wanted): those this exchange found neither in the folder nor fetched beside it (missing: their content’s hash and size) join; those it found (there), and those no change waits for any more (written, or another change came), leave. Those of changes it did not look at (not read this time, hurried) stay. Nothing read nor written while nothing waits.