Shutdown

Triggers a reaction once during system shutdown for cleanup.

Syntax

on<Shutdown>().then([] {
    // Runs once when the system is shutting down
});

Behavior

Shutdown fires after PowerPlant::shutdown() is called. At this point the thread pool is still active, allowing shutdown tasks to perform cleanup work such as closing connections, flushing buffers, or saving state.

graph LR
    A[Install Reactors] --> B["PowerPlant::start()"]
    B --> C[Startup reactions fire]
    C --> D[Normal execution]
    D --> E["PowerPlant::shutdown()"]
    E --> F[Shutdown reactions fire]
    F --> G[Threads joined]

After all Shutdown tasks complete, the thread pool threads are joined and the PowerPlant terminates. Each Shutdown reaction runs exactly once per PowerPlant lifecycle.

Example

#include <nuclear>

class CleanupReactor : public NUClear::Reactor {
public:
    CleanupReactor(std::unique_ptr<NUClear::Environment> environment) : Reactor(std::move(environment)) {

        on<Shutdown>().then([this] {
            log<INFO>("System shutting down, cleaning up...");
            close_connections();
            flush_buffers();
        });
    }
};

Notes

• Shutdown fires only once — it cannot re-trigger.
• The thread pool is still active during Shutdown, so tasks execute normally.
• After shutdown begins, no new non-inline tasks can be submitted. If a Shutdown reaction emits a message (non-inline), the triggered reactions will not execute. Only emit<Scope::INLINE> works during shutdown.
• Common uses: close connections, flush buffers, save state, log shutdown info.
• After all Shutdown reactions complete, threads are joined and the PowerPlant exits.

See Also

• Startup — trigger a reaction when the system starts
• Once — ensure any reaction runs exactly once
• Lifecycle — full PowerPlant lifecycle explanation