EventBus (generic)

Header defines the type-erased event bus layer that powers FLOX fan-out delivery, plus two compile-time policies and supporting concepts/traits.

Key Pieces

Piece	Role
SyncPolicy<Event>	Wraps each event with a TickBarrier*, enforcing all subscribers finished semantics (deterministic backtests).
AsyncPolicy<Event>	Pass-through event delivery — publisher returns immediately (live trading).
concepts::EventBus	Compile-time contract (publish, subscribe, getQueue, currentTickId, enableDrainOnStop).
traits::EventBusTrait	Generates a static v-table for any concrete bus that satisfies the concept.
EventBusRef<Event, Queue>	Lightweight handle {void*, VTable*} that forwards calls without virtual inheritance.

EventBusRef API

EventBusRef<Event, Queue> bus = …;

bus.start();                       // subsystem lifecycle
bus.publish(event);                // fan-out
bus.subscribe(listener);           // add subscriber
auto q  = bus.getQueue(id);        // direct queue access (optional)
auto t  = bus.currentTickId();     // monotonic tick counter
bus.enableDrainOnStop();           // wait for queues to empty on stop()

Choosing a Policy

using BookUpdateBus = EventBus<
    pool::Handle<BookUpdateEvent>,
#ifdef USE_SYNC_MARKET_BUS
    SyncPolicy<pool::Handle<BookUpdateEvent>>
#else
    AsyncPolicy<pool::Handle<BookUpdateEvent>>
#endif
>;

Define / undefine USE_SYNC_* macros before including the header to switch between deterministic and low-latency modes.

Notes

• Neither policy allocates after construction; queues are pre-sized.
• EventBusRef itself is trivially copyable and can be passed by value.