Module runtime 

The centralized Tokio runtime for a running Nautilus system.

Design rationale

NautilusTrader uses a single global Tokio runtime because:

• A single long-lived runtime avoids repeated startup/shutdown overhead.
• The runtime is lazily initialized on first call to get_runtime() via OnceLock.
• Worker thread count is configurable via the NAUTILUS_WORKER_THREADS environment variable.

Python support

When the python feature is enabled, the runtime initializes the Python interpreter before starting worker threads. The PyO3 module registers an atexit handler via shutdown_runtime() to cleanly shut down when Python exits.

Testing considerations

The global runtime pattern makes it harder to inject test doubles. For testing:

• Unit tests can use #[tokio::test] which creates its own runtime.
• Integration tests should be aware they share the global runtime state.

Functions

get_runtime

Returns a reference to the global Nautilus Tokio runtime.

shutdown_runtime

Provides a best-effort flush for runtime tasks during shutdown.