Interface ApiService (2.4.0)

An object with an operational state, plus asynchronous #startAsync() and #stopAsync() lifecycle methods to transition between states. Example services include webservers, RPC servers and timers.

The normal lifecycle of a service is:

• NEW ->
• STARTING ->
• RUNNING ->
• STOPPING ->
• TERMINATED

There are deviations from this if there are failures or if ApiService#stopAsync is called before the ApiService reaches the RUNNING state. The set of legal transitions form a DAG, therefore every method of the listener will be called at most once. N.B. The State#FAILED and State#TERMINATED states are terminal states, once a service enters either of these states it cannot ever leave them.

Implementors of this interface are strongly encouraged to extend AbstractApiService which implement this interface and make the threading and state management easier.

Similar to Guava's Service, but redeclared so that Guava could be shaded.

Registers a Listener to be executed on the given executor. The listener will have the corresponding transition method called whenever the service changes state. The listener will not have previous state changes replayed, so it is suggested that listeners are added before the service starts.

addListener guarantees execution ordering across calls to a given listener but not across calls to multiple listeners. Specifically, a given listener will have its callbacks invoked in the same order as the underlying service enters those states. Additionally, at most one of the listener's callbacks will execute at once. However, multiple listeners' callbacks may execute concurrently, and listeners may execute in an order different from the one in which they were registered.

RuntimeExceptions thrown by a listener will be caught and logged. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException) will be caught and logged.

Waits for the ApiService to reach the running state.