Services.Once (fnord v0.9.38)
View SourceThis module provides a mechanism to perform actions only once, using a unique key provided by the caller to determine whether the action has already been performed this session.
The agent is tree-scoped rather than VM-global: start_link/0 starts an
unnamed agent and registers it for the current process tree via
Services.Instance. Each instance root (a test, a Fnord.Instance
checkout, or the escript's main process in production) gets its own notion
of "once", so seen-keys cannot leak between trees sharing a BEAM.
Summary
Functions
Returns a specification to start this module under a supervisor.
Checks if a key has been seen before. If the key has not been seen, it
returns {:error, :not_seen}. If the key has been seen, it returns {:ok, value} where value is the value associated with the key, or true if no
value was specified.
Run the given zero-arity function only once per unique key. Subsequent calls with the same key will be ignored.
True when a Services.Once instance is running in the current process tree. Callers that may be exercised outside a live session (without the service roster running) use this to no-op instead of crashing.
Marks a key as seen. If the key has not been seen before, it returns true
and updates the internal state. If the key has already been seen, it returns
false without updating the state.
Starts the agent that keeps track of seen keys and registers it as the current process tree's instance.
Functions
Returns a specification to start this module under a supervisor.
See Supervisor.
Checks if a key has been seen before. If the key has not been seen, it
returns {:error, :not_seen}. If the key has been seen, it returns {:ok, value} where value is the value associated with the key, or true if no
value was specified.
Run the given zero-arity function only once per unique key. Subsequent calls with the same key will be ignored.
@spec running?() :: boolean()
True when a Services.Once instance is running in the current process tree. Callers that may be exercised outside a live session (without the service roster running) use this to no-op instead of crashing.
Marks a key as seen. If the key has not been seen before, it returns true
and updates the internal state. If the key has already been seen, it returns
false without updating the state.
Starts the agent that keeps track of seen keys and registers it as the current process tree's instance.
Emits a warning (using UI.warn/1) if the message has not yet been emitted
during this session.