Startup

Triggers a reaction once when the PowerPlant starts execution.

Syntax

on<Startup>().then([] {
    // Runs once when the system starts
});

Behavior

Startup fires after all reactors have been installed and PowerPlant::start() is called. All Startup reactions execute before the scheduler begins processing the general task queue. This guarantees that any data emitted during Startup is available before normal reactions begin executing.

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

Startup is emitted inline, meaning all Startup reactions complete before start() returns control to the scheduler. Each Startup reaction runs exactly once per PowerPlant lifecycle.

Example

#include <nuclear>

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

        on<Startup>().then([this] {
            log<INFO>("System started, emitting initial configuration");
            emit(std::make_unique<Config>(load_config()));
        });
    }
};

Notes

• Startup fires only once — it cannot re-trigger.
• Common uses: emit initial data, open connections, log startup diagnostics.
• Tasks run on the default thread pool, so they are subject to normal scheduling.
• All reactors are fully installed before any Startup reaction fires.

See Also

• Shutdown — trigger a reaction during system shutdown
• Once — ensure any reaction runs exactly once
• Lifecycle — full PowerPlant lifecycle explanation