In theoretically, the game account will be synchronized with the game progress. However in real case, transaction finalty takes time, sometimes could be much longer than expected. So the data on game account is usually delayed from the game progress. To complicate things further, we need to get players to join the game through the contract, the new player information is updated in real time. So the game account is synchronized with game progress in an bidirected asynchronized way.
Considering follow case,
Nodes could be either server or client. We requires all nodes have
the same calculation all the time. So when node B initializing the
game state, even though player C is already in game, it should be
excluded from the game. Otherwise, node A and B would have different
states from the calculation. To solve this, we introduce a version
number: access_version. It will be increased by 1 every time a
player or server joined. And each join takes current version as its
own access_version. When initiating the game state, we use
access_version to filter out who is already in game at the time.
Another version number is called settle_version, which indicates how
many times the game has been settled. Each settlement will result in
an increment. This number can represent a version of a state of
players' assets. Events and deposits will be tagged with
settle_version. So everyone can accumulate current state by
initiating from current on-chain account, access_version and
settle_version.
This graph illustrated how how game state is sychronized between on-chain account, transactor and other nodes.
S(n) means the settle event with settle_version = n. E(n) means the normal event with settle_version = n.
We also use settle version to represent a deposit in further. Usually the player deposit in the middle of the game can't be handled instantly. So when a deposit transaction is handled, a deposit record will be stored in game account with a settle_version which is greater than the account's. It means this deposit will be collected in future.
