io.atomix.copycat.session

Enum Session.State

java.lang.Object

java.lang.Enum<Session.State>

io.atomix.copycat.session.Session.State

All Implemented Interfaces:

Serializable, Comparable<Session.State>

Enclosing interface:

Session

public static enum Session.State
extends Enum<Session.State>

Represents the state of a session.

Throughout the lifetime of a session, the session may change state as a result of communication or the lack thereof between the client and the cluster. See the specific states for more documentation.

Enum Constant Summary

Enum Constants

Enum Constant and Description
CLOSED Indicates that the session has been closed.
EXPIRED Indicates that the session is expired.
OPEN Indicates that the session is connected and open.
UNSTABLE Indicates that the session in an unstable state and may or may not be EXPIRED.

Method Summary

Modifier and Type	Method and Description
boolean	active() Returns a boolean value indicating whether the state is an active state.
static Session.State	valueOf(String name) Returns the enum constant of this type with the specified name.
static Session.State[]	values() Returns an array containing the constants of this enum type, in the order they are declared.

Methods inherited from class java.lang.Enum

compareTo, equals, getDeclaringClass, hashCode, name, ordinal, toString, valueOf

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Enum Constant Detail

OPEN

public static final Session.State OPEN

Indicates that the session is connected and open.

This is the initial state of a session upon registration. Once the session is registered with the cluster, the session's state will be OPEN and will remain open so long as the client is able to communicate with the cluster to keep its session alive.

Clients withe a session in the OPEN state can be assumed to be operating normally and are guaranteed to benefit from linearizable reads and writes.

UNSTABLE

public static final Session.State UNSTABLE

Indicates that the session in an unstable state and may or may not be EXPIRED.

The unstable state is indicative of a state in which a client is unable to communicate with the cluster and therefore cannot determine whether its session is or is not expired. Until the client is able to re-establish communication with the cluster, its session will remain in this state. While in the UNSTABLE state, users of the client should assume that the session may have been expired and that other clients may react to the client having been expired while in the unstable state.

Commands submitted or completed in the UNSTABLE state may not be linearizable. An unstable session may be expired and a client may have to resubmit associated commands once a new session in registered. This can lead to duplicate commands being applied to servers state machines, thus breaking linearizability.

Once the client is able to re-establish communication with the cluster again it will determine whether the session is still active or indeed has been expired. The session will either transition back to the OPEN state or EXPIRED based on feedback from the cluster. Only the cluster can explicitly expire a session.

EXPIRED

public static final Session.State EXPIRED

Indicates that the session is expired.

Once an UNSTABLE client re-establishes communication with the cluster, the cluster may indicate to the client that its session has been expired. In that case, the client may no longer submit operations under the expired session and must register a new session to continue operating on server state machines.

When a client's session is expired, commands submitted under the expired session that have not yet been completed may or may not be applied to server state machines. Linearizability is guaranteed only within the context of a session, and so linearizability may be broken if operations are resubmitted across sessions.

CLOSED

public static final Session.State CLOSED

Indicates that the session has been closed.

This state indicates that the client's session was explicitly unregistered and the session was closed safely.

Method Detail

values

public static Session.State[] values()

Returns an array containing the constants of this enum type, in the order they are declared. This method may be used to iterate over the constants as follows:

for (Session.State c : Session.State.values())
    System.out.println(c);

Returns:

an array containing the constants of this enum type, in the order they are declared

valueOf

public static Session.State valueOf(String name)

Returns the enum constant of this type with the specified name. The string must match exactly an identifier used to declare an enum constant in this type. (Extraneous whitespace characters are not permitted.)

Parameters:

name - the name of the enum constant to be returned.

Returns:

the enum constant with the specified name

Throws:

IllegalArgumentException - if this enum type has no constant with the specified name

NullPointerException - if the argument is null

active

public boolean active()

Returns a boolean value indicating whether the state is an active state.

Sessions can only submit commands and receive events while in an active state.

Returns:

Indicates whether the state is an active state.