Module org.jgroups.raft
Package org.jgroups.raft

Interface StateMachine

All Known Implementing Classes:
CounterService, CounterStateMachine, ReplicatedStateMachine, ReplStateMachine
public interface StateMachine
Interface of a state machine which stores data in memory. Committed log entries are applied to the state machine.
Since:
0.1
Author:
Bela Ban

  • Method Summary

    Modifier and Type
    Method
    Description
    byte[]
    apply(byte[] data, int offset, int length, boolean serialize_response)
    Applies a command to the state machine.
    void
    readContentFrom(DataInput in)
    Reads the contents of the state machine from an input stream.
    void
    writeContentTo(DataOutput out)
    Writes the contents of the state machine to an output stream.

  • Method Details

    • apply

      byte[] apply(byte[] data, int offset, int length, boolean serialize_response) throws Exception
      Applies a command to the state machine. The contents of the byte[] buffer are interpreted by the state machine. The command could for example be a set(), remove() or clear() command.
      Parameters:
      data - The byte[] buffer
      offset - The offset at which the data starts
      length - The length of the data
      serialize_response - If true, serialize and return the response, else return null
      Returns:
      A serialized response value, or null (e.g. if the method returned void)
      Throws:
      Exception - Thrown on deserialization or other failure

    • readContentFrom

      void readContentFrom(DataInput in) throws Exception
      Reads the contents of the state machine from an input stream.

      This can be the case when an InstallSnapshot RPC is used to bootstrap a new node, or a node that's lagging far behind. The parsing depends on the concrete state machine implementation, but the idea is that the stream is a sequence of commands, each of which can be passed to apply(byte[], int, int, boolean).

      The state machine may need to block modifications until the contents have been set (unless e.g. copy-on-write is used). The state machine implementation may need to remove all contents before populating itself from the stream.

      Parameters:
      in - The input stream
      Throws:
      Exception

    • writeContentTo

      void writeContentTo(DataOutput out) throws Exception
      Writes the contents of the state machine to an output stream. This is typically called on the leader to provide state to a new node, or a node that's lagging far behind.

      Updates to the state machine may need to be put on hold while the state is written to the output stream.

      Parameters:
      out - The output stream
      Throws:
      Exception