Service Layer - Orch
Finally, to make it more convenient for building services, SONiC provides another layer of abstraction on top of the communication layer, offering a base class for services: Orch.
With all the lower layers, adding message communication support in Orch is relatively straightforward. The main class diagram is shown below:
Note: Since this layer is part of the service layer, the code lives in the sonic-swss repository, not in sonic-swss-common. In addition to message communication, this class also provides many other utility functions related to service implementation (for example, log files, etc.).
We can see that Orch mainly wraps SubscriberStateTable and ConsumerStateTable to simplify and unify the message subscription. The core code is very simple and creates different Consumers based on the database type:
void Orch::addConsumer(DBConnector *db, string tableName, int pri)
{
if (db->getDbId() == CONFIG_DB || db->getDbId() == STATE_DB || db->getDbId() == CHASSIS_APP_DB) {
addExecutor(
new Consumer(
new SubscriberStateTable(db, tableName, TableConsumable::DEFAULT_POP_BATCH_SIZE, pri),
this,
tableName));
} else {
addExecutor(
new Consumer(
new ConsumerStateTable(db, tableName, gBatchSize, pri),
this,
tableName));
}
}