Package com.google.common.util.concurrent

Class ServiceManager

  • @Beta
@Singleton
public final class ServiceManager
extends java.lang.Object
    A manager for monitoring and controlling a set of services. This class provides methods for starting, stopping and inspecting a collection of services. Additionally, users can monitor state transitions with the listener mechanism.

    While it is recommended that service lifecycles be managed via this class, state transitions initiated via other mechanisms do not impact the correctness of its methods. For example, if the services are started by some mechanism besides startAsync(), the listeners will be invoked when appropriate and awaitHealthy() will still work as expected.

    Here is a simple example of how to use a ServiceManager to start a server. 

       
 class Server {
   public static void main(String[] args) {
     Set<Service> services = ...;
     ServiceManager manager = new ServiceManager(services);
     manager.addListener(new Listener() {
         public void stopped() {}
         public void healthy() {
           // Services have been initialized and are healthy, start accepting requests...
         }
         public void failure(Service service) {
           // Something failed, at this point we could log it, notify a load balancer, or take
           // some other action.  For now we will just exit.
           System.exit(1);
         }
       },
       MoreExecutors.sameThreadExecutor());

     Runtime.getRuntime().addShutdownHook(new Thread() {
       public void run() {
         // Give the services 5 seconds to stop to ensure that we are responsive to shutdown 
         // requests.
         try {
           manager.stopAsync().awaitStopped(5, TimeUnit.SECONDS);
         } catch (TimeoutException timeout) {
           // stopping timed out
         }
       }
     });
     manager.startAsync();  // start all the services asynchronously
   }
 }

    This class uses the ServiceManager's methods to start all of its services, to respond to service failure and to ensure that when the JVM is shutting down all the services are stopped.

    Since:
    14.0

    • Constructor Detail

      • ServiceManager

        public ServiceManager​(java.lang.Iterable<? extends Service> services)
        Constructs a new instance for managing the given services.
        Parameters:
        services - The services to manage
        Throws:
        java.lang.IllegalArgumentException - if not all services are new or if there are any duplicate services.

    • Method Detail

      • addListener

        public void addListener​(ServiceManager.Listener listener,
                        java.util.concurrent.Executor executor)
        Registers a ServiceManager.Listener to be executed on the given executor. The listener will not have previous state changes replayed, so it is suggested that listeners are added before any of the managed services are started.

        There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called whenever there is a state change.

        Exceptions thrown by a listener will be propagated up to the executor. Any exception thrown during Executor.execute (e.g., a RejectedExecutionException or an exception thrown by inline execution) will be caught and logged.

        For fast, lightweight listeners that would be safe to execute in any thread, consider calling addListener(Listener).

        Parameters:
        listener - the listener to run when the manager changes state
        executor - the executor in which the listeners callback methods will be run.

      • addListener

        public void addListener​(ServiceManager.Listener listener)
        Registers a ServiceManager.Listener to be run when this ServiceManager changes state. The listener will not have previous state changes replayed, so it is suggested that listeners are added before any of the managed services are started.

        There is no guaranteed ordering of execution of listeners, but any listener added through this method is guaranteed to be called whenever there is a state change.

        Exceptions thrown by a listener will be will be caught and logged.

        Parameters:
        listener - the listener to run when the manager changes state

      • startAsync

        public ServiceManager startAsync()
        Initiates service startup on all the services being managed. It is only valid to call this method if all of the services are new.
        Returns:
        this
        Throws:
        java.lang.IllegalStateException - if any of the Services are not new when the method is called.

      • awaitHealthy

        public void awaitHealthy()
        Waits for the ServiceManager to become healthy. The manager will become healthy after all the component services have reached the running state.
        Throws:
        java.lang.IllegalStateException - if the service manager reaches a state from which it cannot become healthy.

      • awaitHealthy

        public void awaitHealthy​(long timeout,
                         java.util.concurrent.TimeUnit unit)
                  throws java.util.concurrent.TimeoutException
        Waits for the ServiceManager to become healthy for no more than the given time. The manager will become healthy after all the component services have reached the running state.
        Parameters:
        timeout - the maximum time to wait
        unit - the time unit of the timeout argument
        Throws:
        java.util.concurrent.TimeoutException - if not all of the services have finished starting within the deadline
        java.lang.IllegalStateException - if the service manager reaches a state from which it cannot become healthy.

      • stopAsync

        public ServiceManager stopAsync()
        Initiates service shutdown if necessary on all the services being managed.
        Returns:
        this

      • awaitStopped

        public void awaitStopped()
        Waits for the all the services to reach a terminal state. After this method returns all services will either be terminated or failed

      • awaitStopped

        public void awaitStopped​(long timeout,
                         java.util.concurrent.TimeUnit unit)
                  throws java.util.concurrent.TimeoutException
        Waits for the all the services to reach a terminal state for no more than the given time. After this method returns all services will either be terminated or failed
        Parameters:
        timeout - the maximum time to wait
        unit - the time unit of the timeout argument
        Throws:
        java.util.concurrent.TimeoutException - if not all of the services have stopped within the deadline

      • isHealthy

        public boolean isHealthy()
        Returns true if all services are currently in the running state.

        Users who want more detailed information should use the servicesByState() method to get detailed information about which services are not running.

      • servicesByState

        public ImmutableMultimap<Service.State,​Service> servicesByState()
        Provides a snapshot of the current state of all the services under management.

        N.B. This snapshot it not guaranteed to be consistent, i.e. the set of states returned may not correspond to any particular point in time view of the services.

      • startupTimes

        public ImmutableMap<Service,​java.lang.Long> startupTimes()
        Returns the service load times. This value will only return startup times for services that have finished starting.
        Returns:
        Map of services and their corresponding startup time in millis, the map entries will be ordered by startup time.

      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object