com.google.common.util.concurrent

Class ServiceManager

java.lang.Object

com.google.common.util.concurrent.ServiceManager

@GwtIncompatible
public final class ServiceManager
extends 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.directExecutor());

     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

Author:

Luke Sandberg

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ServiceManager.Listener A listener for the aggregate state changes of the services that are under management.

Constructor Summary

Constructors

Constructor and Description
ServiceManager(Iterable<? extends Service> services) Constructs a new instance for managing the given services.

Method Summary

Modifier and Type	Method and Description
void	addListener(ServiceManager.Listener listener) Deprecated. Use the overload that accepts an executor. For equivalent behavior, pass MoreExecutors.directExecutor(). However, consider whether another executor would be more appropriate, as discussed in the docs for ListenableFuture.addListener. This method is scheduled for deletion in October 2020.
void	addListener(ServiceManager.Listener listener, Executor executor) Registers a ServiceManager.Listener to be executed on the given executor.
void	awaitHealthy() Waits for the ServiceManager to become healthy.
void	awaitHealthy(long timeout, TimeUnit unit) Waits for the ServiceManager to become healthy for no more than the given time.
void	awaitStopped() Waits for the all the services to reach a terminal state.
void	awaitStopped(long timeout, TimeUnit unit) Waits for the all the services to reach a terminal state for no more than the given time.
boolean	isHealthy() Returns true if all services are currently in the running state.
ImmutableSetMultimap<Service.State,Service>	servicesByState() Provides a snapshot of the current state of all the services under management.
ServiceManager	startAsync() Initiates service startup on all the services being managed.
ImmutableMap<Service,Long>	startupTimes() Returns the service load times.
ServiceManager	stopAsync() Initiates service shutdown if necessary on all the services being managed.
String	toString() Returns a string representation of the object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ServiceManager

public ServiceManager(Iterable<? extends Service> services)

Constructs a new instance for managing the given services.

Parameters:

services - The services to manage

Throws:

IllegalArgumentException - if not all services are new or if there are any duplicate services.

Method Detail

addListener

public void addListener(ServiceManager.Listener listener,
                        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.

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.

When selecting an executor, note that directExecutor is dangerous in some cases. See the discussion in the ListenableFuture.addListener documentation.

Parameters:

listener - the listener to run when the manager changes state

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

addListener

@Beta
 @Deprecated
public void addListener(ServiceManager.Listener listener)

Deprecated. Use the overload that accepts an executor. For equivalent behavior, pass MoreExecutors.directExecutor(). However, consider whether another executor would be more appropriate, as discussed in the docs for ListenableFuture.addListener. This method is scheduled for deletion in October 2020.

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.

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.

Parameters:

listener - the listener to run when the manager changes state

Since:

15.0

startAsync

@CanIgnoreReturnValue
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:

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:

IllegalStateException - if the service manager reaches a state from which it cannot become healthy.

awaitHealthy

public void awaitHealthy(long timeout,
                         TimeUnit unit)
                  throws 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:

TimeoutException - if not all of the services have finished starting within the deadline

IllegalStateException - if the service manager reaches a state from which it cannot become healthy.

stopAsync

@CanIgnoreReturnValue
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,
                         TimeUnit unit)
                  throws 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:

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 ImmutableSetMultimap<Service.State,Service> servicesByState()

Provides a snapshot of the current state of all the services under management.

N.B. This snapshot is guaranteed to be consistent, i.e. the set of states returned will correspond to a point in time view of the services.

Since:

29.0 (present with return type ImmutableMultimap since 14.0)

startupTimes

public ImmutableMap<Service,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 String toString()

Description copied from class: java.lang.Object

Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of:

 getClass().getName() + '@' + Integer.toHexString(hashCode())
 

Overrides:

toString in class Object

Returns:

a string representation of the object.