The standard library oneshot_maildrop package implements in essence concurrency-safe refcells specialized to being set only once. These are often used for return values from interthread messages.
The oneshot_maildrop package implements the Oneshot_Maildrop API.
The oneshot_maildrop package source code is in src/lib/src/lib/thread-kit/src/core-thread-kit/oneshot-maildrop.pkg.
See also: maildrop.
The above information is manually maintained and may contain errors.