Package io.prestosql.execution

Class StateMachine<T>

java.lang.Object

io.prestosql.execution.StateMachine<T>

@ThreadSafe
public class StateMachine<T>
extends Object

Simple state machine which holds a single state. Callers can register for state change events.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	StateMachine.StateChangeListener<T>

Constructor Summary

Constructors

Constructor	Description
StateMachine(String name, Executor executor, T initialState)	Creates a state machine with the specified initial state and no terminal states.
StateMachine(String name, Executor executor, T initialState, Iterable<T> terminalStates)	Creates a state machine with the specified initial state and terminal states.

Method Summary

Modifier and Type	Method	Description
void	addStateChangeListener(StateMachine.StateChangeListener<T> stateChangeListener)	Adds a listener to be notified when the state instance changes according to .equals().
boolean	compareAndSet(T expectedState, T newState)	Sets the state if the current state .equals() the specified expected state.
T	get()
com.google.common.util.concurrent.ListenableFuture<T>	getStateChange(T currentState)	Gets a future that completes when the state is no longer .equals() to currentState).
T	set(T newState)	Sets the state.
boolean	setIf(T newState, Predicate<T> predicate)	Sets the state if the current state satisfies the specified predicate.
String	toString()
T	trySet(T newState)	Tries to change the state.

Methods inherited from class java.lang.Object

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

Constructor Detail

StateMachine

public StateMachine(String name,
                    Executor executor,
                    T initialState)

Creates a state machine with the specified initial state and no terminal states.

Parameters:

name - name of this state machine to use in debug statements

executor - executor for firing state change events; must not be a same thread executor

initialState - the initial state

StateMachine

public StateMachine(String name,
                    Executor executor,
                    T initialState,
                    Iterable<T> terminalStates)

Creates a state machine with the specified initial state and terminal states.

Parameters:

name - name of this state machine to use in debug statements

executor - executor for firing state change events; must not be a same thread executor

initialState - the initial state

terminalStates - the terminal states

Method Detail

get

public T get()

set

public T set(T newState)

Sets the state. If the new state does not .equals() the current state, listeners and waiters will be notified.

Returns:

the old state

Throws:

IllegalStateException - if state change would cause a transition from a terminal state

trySet

public T trySet(T newState)

Tries to change the state. State will not change if the new state .equals() the current state, of if the current state is a terminal state. If the state changed, listeners and waiters will be notified.

Returns:

the state before the possible state change

setIf

public boolean setIf(T newState,
                     Predicate<T> predicate)

Sets the state if the current state satisfies the specified predicate. If the new state does not .equals() the current state, listeners and waiters will be notified.

Returns:

true if the state is set

compareAndSet

public boolean compareAndSet(T expectedState,
                             T newState)

Sets the state if the current state .equals() the specified expected state. If the new state does not .equals() the current state, listeners and waiters will be notified.

Returns:

true if the state is set

getStateChange

public com.google.common.util.concurrent.ListenableFuture<T> getStateChange(T currentState)

Gets a future that completes when the state is no longer .equals() to currentState).

addStateChangeListener

public void addStateChangeListener(StateMachine.StateChangeListener<T> stateChangeListener)

Adds a listener to be notified when the state instance changes according to .equals(). Listener is always notified asynchronously using a dedicated notification thread pool so, care should be taken to avoid leaking this when adding a listener in a constructor. Additionally, it is possible notifications are observed out of order due to the asynchronous execution. The listener is immediately notified immediately of the current state.

toString

public String toString()

Overrides:

toString in class Object