Package com.google.api.core

Interface ApiService

All Known Implementing Classes:
AbstractApiService
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:

There are deviations from this if there are failures or if 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 ApiService.State.FAILED and ApiService.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.

  • Method Details

    • addListener

      void addListener(ApiService.Listener listener, Executor executor)
      Registers a ApiService.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:
      listener - the listener to run when the service changes state is complete
      executor - the executor in which the listeners callback methods will be run.

    • awaitRunning

      void awaitRunning()
      Waits for the ApiService to reach the running state.
      Throws:
      IllegalStateException - if the service reaches a state from which it is not possible to enter the ApiService.State.RUNNING state. e.g. if the state is State#TERMINATED when this method is called then this will throw an IllegalStateException.

    • awaitRunning

      void awaitRunning(long timeout, TimeUnit unit) throws TimeoutException
      Waits for the ApiService to reach the running state for no more than the given time.
      Parameters:
      timeout - the maximum time to wait
      unit - the time unit of the timeout argument
      Throws:
      TimeoutException - if the service has not reached the given state within the deadline
      IllegalStateException - if the service reaches a state from which it is not possible to enter the RUNNING state. e.g. if the state is State#TERMINATED when this method is called then this will throw an IllegalStateException.

    • awaitTerminated

      void awaitTerminated()
      Waits for the ApiService to reach the terminated state.
      Throws:
      IllegalStateException - if the service fails.

    • awaitTerminated

      void awaitTerminated(long timeout, TimeUnit unit) throws TimeoutException
      Waits for the ApiService to reach a terminal state (either terminated or failed) for no more than the given time.
      Parameters:
      timeout - the maximum time to wait
      unit - the time unit of the timeout argument
      Throws:
      TimeoutException - if the service has not reached the given state within the deadline
      IllegalStateException - if the service fails.

    • failureCause

      Throwable failureCause()
      Returns the Throwable that caused this service to fail.
      Throws:
      IllegalStateException - if this service's state isn't FAILED.

    • isRunning

      boolean isRunning()
      Returns true if this service is running.

    • startAsync

      ApiService startAsync()
      If the service state is ApiService.State.NEW, this initiates service startup and returns immediately. A stopped service may not be restarted.
      Returns:
      this
      Throws:
      IllegalStateException - if the service is not ApiService.State.NEW

    • state

      ApiService.State state()
      Returns the lifecycle state of the service.

    • stopAsync

      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:
      this