CAS (compare-and-swap)

Introduction

CAS (compare-and-swap) is a mechanism that allows you to update a key-value pair only if the current value matches the expected value.

The basic CAS (Compare And Swap) API is

CasResponse cas(CasRequest request) throws GoblinException;

CasRequest:

Field	Type	Remark
key	KeyType	The key to be put into Goblin
value	ValueType	The value to be put into Goblin with respect to key
enableTTL	Boolean	true: TTL (time to live) will be enabled for the key false: no TTL will be enabled for the key
ttl	Integer	The TTL for the key (in seconds, should be larger than zero), if enableTTL is true. This value could be null to reset the start time of the last TTL.
comparedVersion	Long	Only update the value for the key if the latest version in Goblin equals to comparedVersion. Otherwise, throw a GoblinConditionNotMetException.

CasResponse:

Field	Type	Remark
version	Long	The version of the key that was put into Goblin

CAS without TTL

CasResponse cas(KeyType key, ValueType value, long comparedVersion) throws GoblinException;

CAS with a defined TTL

CasResponse casWithTTL(KeyType key, ValueType value, long comparedVersion, Integer ttl) throws GoblinException;

CAS with the last TTL, reset the start time of the TTL

CasResponse casWithTTL(KeyType key, ValueType value, long comparedVersion) throws GoblinException;

When client updates a key-value pair, it sets an expected version of the target key as a condition in the request.
Server checks if the current version of the key matches the expected version. If yes, server updates the key-value pair and returns true to the client. Otherwise, server returns false to the client.