5.2 Read-only message processing
Some accounts may be able to process operations in a pass/fail manner without having to modify their internal status. In this case, as long as the read-only message handlers of a specific account are contained in one or more threads in a specific cycle, these handlers can be executed concurrently.
5.3 Multi-account atomic transaction
Sometimes, it is better to ensure that actions are delivered and accepted atomically by multiple accounts. In this case, both operations are placed in the same transaction, the two accounts are assigned to the same thread, and the messages are executed in sequence.
5.4 Partially assess the state of the blockchain
Large-scale blockchain technology components should be modular. It is not required that everyone run everything, especially when someone only needs to use a small part of the application.
Exchange application developers run full nodes to display exchange status to their users. This exchange application does not require status related to social media applications. EOS.IO allows any full node to select any subset of the application to run, and messages passed to other applications will be safely ignored, because the state of the application comes entirely from the messages passed to it, rather than relying on other applications.