org.apache.mesos.state

Interface State

All Known Implementing Classes:

AbstractState, InMemoryState, LevelDBState, LogState, ZooKeeperState

public interface State

An abstraction of "state" (possibly between multiple distributed components) represented by "variables" (effectively key/value pairs). Variables are versioned such that setting a variable in the state will only succeed if the variable has not changed since last fetched. Varying implementations of state provide varying replicated guarantees.

Note that the semantics of 'fetch' and 'store' provide atomicity. That is, you can not store a variable that has changed since you did the last fetch. That is, if a store succeeds then no other writes have been performed on the variable since your fetch. Example:

 State state = new ZooKeeperState();
   Future<Variable> variable = state.fetch("machines");
   Variable machines = variable.get();
   machines = machines.mutate(...);
   variable = state.store(machines);
   machines = variable.get();
 
 

Method Summary

Methods

Modifier and Type	Method and Description
Future<Boolean>	expunge(Variable variable) Returns true if successfully expunged the variable from the state or false if the variable did not exist or was no longer valid.
Future<Variable>	fetch(String name) Returns an immutable "variable" representing the current value from the state associated with the specified name.
Future<Iterator<String>>	names() Returns an iterator of variable names in the state.
Future<Variable>	store(Variable variable) Returns an immutable "variable" representing the current value in the state if updating the specified variable in the state was successful, otherwise returns null.

Method Detail

fetch

Future<Variable> fetch(String name)

Returns an immutable "variable" representing the current value from the state associated with the specified name.

Parameters:

name - The name of the variable.

Returns:

A future of the variable.

See Also:

Variable

store

Future<Variable> store(Variable variable)

Returns an immutable "variable" representing the current value in the state if updating the specified variable in the state was successful, otherwise returns null.

Parameters:

variable - The variable to be stored.

Returns:

A future of a variable with the new value on success, or null on failure.

See Also:

Variable

expunge

Future<Boolean> expunge(Variable variable)

Returns true if successfully expunged the variable from the state or false if the variable did not exist or was no longer valid.

Parameters:

variable - The variable to be expunged.

Returns:

A future of true on success, false on failure.

See Also:

Variable

names

Future<Iterator<String>> names()

Returns an iterator of variable names in the state.

Returns:

A future of an iterator over all variable names in the state.