Interface ApiService

public interface ApiService

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.

Methods

addListener(ApiService.Listener listener, Executor executor)

public abstract void addListener(ApiService.Listener listener, Executor executor)

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.

Parameters
NameDescription
listenerApiService.Listener

the listener to run when the service changes state is complete

executorExecutor

the executor in which the listeners callback methods will be run.

awaitRunning()

public abstract void awaitRunning()

Waits for the ApiService to reach the running state.

awaitRunning(long timeout, TimeUnit unit)

public abstract void awaitRunning(long timeout, TimeUnit unit)

Waits for the ApiService to reach the running state for no more than the given time.

Parameters
NameDescription
timeoutlong

the maximum time to wait

unitTimeUnit

the time unit of the timeout argument

Exceptions
TypeDescription
TimeoutException

if the service has not reached the given state within the deadline

awaitTerminated()

public abstract void awaitTerminated()

Waits for the ApiService to reach the terminated state.

awaitTerminated(long timeout, TimeUnit unit)

public abstract void awaitTerminated(long timeout, TimeUnit unit)

Waits for the ApiService to reach a terminal state (either terminated or failed) for no more than the given time.

Parameters
NameDescription
timeoutlong

the maximum time to wait

unitTimeUnit

the time unit of the timeout argument

Exceptions
TypeDescription
TimeoutException

if the service has not reached the given state within the deadline

failureCause()

public abstract Throwable failureCause()

Returns the Throwable that caused this service to fail.

Returns
TypeDescription
Throwable

isRunning()

public abstract boolean isRunning()

Returns true if this service is running.

Returns
TypeDescription
boolean

startAsync()

public abstract ApiService startAsync()

If the service state is State#NEW, this initiates service startup and returns immediately. A stopped service may not be restarted.

Returns
TypeDescription
ApiService

this

state()

public abstract ApiService.State state()

Returns the lifecycle state of the service.

Returns
TypeDescription
ApiService.State

stopAsync()

public abstract ApiService stopAsync()

If the service is starting or running, this initiates service shutdown and returns immediately. If the service is new, it is terminated without having been started nor stopped. If the service has already been stopped, this method returns immediately without taking action.

Returns
TypeDescription
ApiService

this