edu.umass.cs.gigapaxos.examples.noop

Class NoopPaxosApp

java.lang.Object

edu.umass.cs.gigapaxos.examples.noop.NoopPaxosApp

All Implemented Interfaces:

Application, AppRequestParser, AppRequestParserBytes, Replicable

public class NoopPaxosApp
extends java.lang.Object
implements Replicable

Author:

arun

Constructor Summary

Constructors

Constructor and Description
NoopPaxosApp()

Method Summary

Modifier and Type	Method and Description
java.lang.String	checkpoint(java.lang.String name) Checkpoints the current application state and returns it.
boolean	execute(Request request)
boolean	execute(Request request, boolean doNotReplyToClient) This method must handle the request atomically and return true if successful or throw an exception or return false.
Request	getRequest(java.lang.String stringified) Needed only if app uses request types other than RequestPacket.
java.util.Set<IntegerPacketType>	getRequestTypes() Needed only if app uses request types other than RequestPacket.
boolean	restore(java.lang.String name, java.lang.String state) Resets the current application state for name to state.

Methods inherited from class java.lang.Object

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

Methods inherited from interface edu.umass.cs.gigapaxos.interfaces.AppRequestParser

getMutualAuthRequestTypes, getRequest, getServerAuthRequestTypes

Constructor Detail

NoopPaxosApp

public NoopPaxosApp()

Method Detail

execute

public boolean execute(Request request)

Specified by:

execute in interface Application

Returns:

True if the request is executed successfully.

execute

public boolean execute(Request request,
                       boolean doNotReplyToClient)

Description copied from interface: Replicable

This method must handle the request atomically and return true if successful or throw an exception or return false. It is the application's responsibility to ensure atomicity, i.e., it should return true iff the request was successfully executed; if it returns false or throws an exception, the application should ensure that the state of the application rolls back any partial execution of this request. If it returns false or throws an exception, the replica coordination protocol may try to re-attempt executing the request.

Specified by:

execute in interface Replicable

doNotReplyToClient - If true, the application is expected to not send a response back to the originating client (say, because this request is part of a post-crash roll-forward or only the "entry replica" that received the request from the client is expected to respond back. If false, the application is expected to either send a response (if any) back to the client via the ClientMessenger interface or delegate response messaging to paxos via the ClientRequest.getResponse() interface.

Returns:

Must return true if and only if the application handled the request successfully. For safety, executing a request must have a deterministic effect on the safety-critical state. If the request is bad and is to be discarded, the application must still return true (after "successfully" discarding it). If the application returns false, the replica coordination protocol (e.g., paxos) might try to repeatedly re-execute it until successful or kill this replica group ( request.getServiceName()) altogether after a limited number of retries, so the replica group may get stuck unless it returns true after a limited number of retries. Thus, with paxos as the replica coordination protocol, returning false is not really an option as paxos has no way to "roll back" a request whose global order has already been agreed upon.

With replica coordination protocols other than paxos, the boolean return value could be used in protocol-specific ways, e.g., a primary-backup protocol might normally execute a request at just one replica but relay the request to one or more backups if the return value of Application.execute(Request) is false.

checkpoint

public java.lang.String checkpoint(java.lang.String name)

Description copied from interface: Replicable

Checkpoints the current application state and returns it.

Specified by:

checkpoint in interface Replicable

Returns:

Returns the checkpoint state. If the application encounters an error while creating the checkpoint, it must retry until successful or throw a RuntimeException. Returning a null value will be interpreted to mean that the application state is indeed null.

Note that state may simply be an app-specific handle, e.g., a file name, representing the state as opposed to the actual state. The application is responsible for interpreting the state returned by Replicable.checkpoint(String) and that supplied in Replicable.restore(String, String) in a consistent manner.

restore

public boolean restore(java.lang.String name,
                       java.lang.String state)

Description copied from interface: Replicable

Resets the current application state for name to state.

Note that state may simply be an app-specific handle, e.g., a file name, representing the state as opposed to the actual state. The application is responsible for interpreting the state returned by Replicable.checkpoint(String) and that supplied in Replicable.restore(String, String) in a consistent manner.

Specified by:

restore in interface Replicable

Returns:

True if the app atomically updated the state successfully. Else, it must throw an exception. If it returns false, the replica coordination protocol may try to repeat the operation until successful causing the application to get stuck.

getRequest

public Request getRequest(java.lang.String stringified)
                   throws RequestParseException

Needed only if app uses request types other than RequestPacket. Refer NoopApp for a more detailed example.

Specified by:

getRequest in interface AppRequestParser

Returns:

Request corresponding to stringified.

Throws:

RequestParseException

getRequestTypes

public java.util.Set<IntegerPacketType> getRequestTypes()

Needed only if app uses request types other than RequestPacket. Refer NoopApp for a more detailed example.

Specified by:

getRequestTypes in interface AppRequestParser

Returns:

The set of request types that the application expects to process.