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Module Conventions

Each module has a file/directory where they store persistent data (if necessary). When module.New is called, the module is responsible for creating and populating that directory. The logic for saving and loading data belongs in persist.go.

Modules that depend on external information (such as the state of consensus) have an update.go to manage fetching and integrating the external information. If that information is coming from another module, a subscription should be used. Module subscription uses a ModuleSubscriber interface (which the subscriber must satisfy) and a ModuleSubscribe method (implemented by the parent module). As the parent module gets updates, it will call ReceiveModuleUpdate (the only method of the ModuleSubscriber interface) on all subscribers, taking care that each subscriber always receives the updates in the correct order. This method of subscription is chosen to keep information flow simple and synchronized - a child module should never have information that the parent module does not (it just causes problems).

For testing, it is often important to know that an update has propagated to all modules. Any module that subscribes to another must also implement a ModuleNotify function in subscriptions.go. ModuleNotify returns a channel down which a struct{} will be sent every time that module receives an update from a parent module. To keep things simple, a module should not subscribe to the parent of another module that it is subscribed to. For example, the transaction pool is subscribed to the consensus set. Therefore, no module should subscribe to both the transaction pool and the consensus set. All consensus set updates should be received through the transaction pool. This helps with synchronization and ensures that no child module ever has information that the parent module has not yet received (desynchronization).

Module Update Flow

consensus -> (host, hostdb, renter, (transaction pool -> miner, wallet))