Understanding Handler States

Once the Handler is started, it processes security definitions retrieved from a TCP connection. Afterwards, the Handler starts listening for book-related market data. Initially, the Handler reconstructs all the books for all available securities. Once reconstruction is accomplished, the Handler listens for incremental updates and processes them accordingly.

Handler States

The table below describes all possible states for the Handler:

• HandlerStates::Stopped The Handler is stopped or has not executed yet.
• HandlerStates::Stopping The Handler is stopping.
• HandlerStates::Started The Handler is started, but no data processing is performed yet.
• HandlerStates::SecurityDefinitionsRecoveryStarted The Handler started gathering product definitions from the TCP stream.
• HandlerStates::SecurityDefinitionsRecoveryFinished The Handler has completed processing product definitions. In normal flow, the Handler moves to HandlerStates::BooksResynchronizationStarted immediately after achieving HandlerStates::SecurityDefinitionsRecoveryFinished. However, in certain cases (for example, when an error occurs while processing product definitions), the Handler may move to the HandlerStates::Stopping state.
• HandlerStates::BooksResynchronizationStarted The Handler switches to this state when it joins the system for market data and starts building the books for all securities whose definitions were obtained at the previous stage. Also, the Handler may enter this stage if a message GAP is detected while maintaining books.

  Note

  Once the Handler moves into this state, books of all types for all securities are no longer valid and are wiped by the Handler. From this moment, the Handler starts rebuilding all books from scratch.

• HandlerStates::BooksResynchronizationFinished The Handler has completed the book recovery process. From this moment, all books are valid and up to date. The Handler continues to listen for changes in the books and notifies listeners of book updates.

Handler States Diagram