Service (Guava: Google Core Libraries for Java 19.0-rc3 API)

All Known Implementing Classes:

AbstractExecutionThreadService, AbstractIdleService, AbstractScheduledService, AbstractService
```
@Beta
public interface Service
```
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 stopAsync() is called before the Service 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 Service.State.FAILED and Service.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 one of the abstract classes in this package which implement this interface and make the threading and state management easier.
Since:

9.0 (in 1.0 as com.google.common.base.Service)

Author:

Jesse Wilson, Luke Sandberg

Nested Class Summary

Nested Classes
Modifier and Type	Interface and Description
`static class`	`Service.Listener` A listener for the various state changes that a `Service` goes through in its lifecycle.
`static class`	`Service.State` The lifecycle states of a service.

Method Summary

Methods
Modifier and Type	Method and Description
`void`	`addListener(Service.Listener listener, Executor executor)` Registers a `Service.Listener` to be executed on the given executor.
`void`	`awaitRunning()` Waits for the `Service` to reach the running state.
`void`	`awaitRunning(long timeout, TimeUnit unit)` Waits for the `Service` to reach the running state for no more than the given time.
`void`	`awaitTerminated()` Waits for the `Service` to reach the terminated state.
`void`	`awaitTerminated(long timeout, TimeUnit unit)` Waits for the `Service` to reach a terminal state (either `terminated` or `failed`) for no more than the given time.
`Throwable`	`failureCause()` Returns the `Throwable` that caused this service to fail.
`boolean`	`isRunning()` Returns `true` if this service is running.
`Service`	`startAsync()` If the service state is `Service.State.NEW`, this initiates service startup and returns immediately.
`Service.State`	`state()` Returns the lifecycle state of the service.
`Service`	`stopAsync()` If the service is starting or running, this initiates service shutdown and returns immediately.

- Method Detail
  - startAsync
```
Service startAsync()
```
    If the service state is Service.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 Service.State.NEW
    Since:
    
    15.0
  - isRunning
```
boolean isRunning()
```
    Returns true if this service is running.
  - state
```
Service.State state()
```
    Returns the lifecycle state of the service.
  - stopAsync
```
Service 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
    Since:
    
    15.0
  - awaitRunning
```
void awaitRunning()
```
    Waits for the Service to reach the running state.
    
    Throws:
    
    IllegalStateException - if the service reaches a state from which it is not possible to enter the Service.State.RUNNING state. e.g. if the state is State#TERMINATED when this method is called then this will throw an IllegalStateException.
    Since:
    
    15.0
  - awaitRunning
```
void awaitRunning(long timeout,
                TimeUnit unit)
                  throws TimeoutException
```
    Waits for the Service 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.
    Since:
    
    15.0
  - awaitTerminated
```
void awaitTerminated()
```
    Waits for the Service to reach the terminated state.
    
    Throws:
    
    IllegalStateException - if the service fails.
    Since:
    
    15.0
  - awaitTerminated
```
void awaitTerminated(long timeout,
                   TimeUnit unit)
                     throws TimeoutException
```
    Waits for the Service 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.
    Since:
    
    15.0
  - failureCause
```
Throwable failureCause()
```
    Returns the Throwable that caused this service to fail.
    
    Throws:
    
    IllegalStateException - if this service's state isn't FAILED.
    Since:
    
    14.0
  - addListener
```
void addListener(Service.Listener listener,
               Executor executor)
```
    Registers a Service.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. For fast, lightweight listeners that would be safe to execute in any thread, consider MoreExecutors.directExecutor().
    Since:
    
    13.0

Interface Service

Nested Class Summary

Method Summary

Method Detail

startAsync

isRunning

state

stopAsync

awaitRunning

awaitRunning

awaitTerminated

awaitTerminated

failureCause

addListener