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EventBus\

Generic lock-free fan-out bus delivering Event objects to multiple subscribers, with compile-time Policy (SyncPolicy/AsyncPolicy) and configurable QueueSize (default config::DEFAULT_EVENTBUS_QUEUE_SIZE).

template <typename Event,
          typename Policy,
          size_t   QueueSize = config::DEFAULT_EVENTBUS_QUEUE_SIZE>
class EventBus;

Highlights

Aspect Details
Queue type SPSCQueue<QueueItem, QueueSize> per subscriber (lock-free).
Subscriber modes PUSH (own thread) or PULL (caller polls queue via getQueue).
Sync vs Async Sync adds TickBarrier* and waits; async enqueues and returns immediately.
Tick numbering _tickCounter auto-fills event.tickSequence if present.
Drain-on-stop Call enableDrainOnStop() → bus finishes remaining items before exit.

Public API

```cpp void subscribe(Listener); void start(); // spin up PUSH threads void stop(); // signal shutdown, join threads void publish(Event); // broadcast to every queue auto getQueue(SubscriberId) -> std::optional>; uint64_t currentTickId() const; void enableDrainOnStop(); ````

Internal Flow

  1. publish() stamps sequence, builds QueueItem via Policy::makeItem().
  2. Each subscriber’s queue receives the item; in sync mode a local TickBarrier enforces deterministic completion.
  3. PUSH listeners loop on try_pop() → Policy::dispatch() until _running becomes false, then optionally drain remaining items.
  4. stop() swaps _subs into a local map so destructors join safely without holding the global _mutex.

Trait & Handle

  • traits::EventBusTrait<Event, Queue> generates a static v-table for any bus satisfying the concepts::EventBus contract.
  • EventBusRef<Event, Queue> is a two-pointer type-erased handle that forwards all calls without virtual inheritance.

Notes

  • No heap allocations after construction; queues are fixed-size.
  • Thread-safe: publisher acquires _mutex only for queue pointers, not for per-event operations.