Skip to main content

Event System

The Event class is a core middleware in LibXR designed for event-driven mechanisms. It supports event registration, triggering, interrupt-safe invocation, and event bridging — making it an essential tool for embedded task collaboration.

Module Features​

  • Register multiple callbacks based on event IDs;
  • Supports triggering in thread/interrupt contexts;
  • Use GetList() for interrupt-safe event triggering;
  • Supports event bridging, allowing event forwarding across modules;
  • Internally implemented using red-black tree + lock-free list for efficient and thread-safe storage.

Quick Start​

Register an Event Callback​

int counter = 0;
LibXR::Event evt;
auto cb = LibXR::Event::Callback::Create(
    [](bool, int *cnt, uint32_t event) {
        (*cnt)++;
        ASSERT(event == 0x10);
    },
    &counter);

evt.Register(0x10, cb);

Trigger Event​

evt.Active(0x10);  // Trigger in normal thread context

Trigger from Interrupt Context (requires pre-caching list)​

// Obtain event list outside of callback
auto list = evt.GetList(0x1234);
// Trigger inside callback/ISR
evt.ActiveFromCallback(list, 0x1234);

Event Binding​

evt_dst.Bind(evt_src, 0xA, 0xB);  // Triggers evt_dst with event 0xB when evt_src triggers 0xA

Class Definition Overview​

  • Event::Register(event, cb): Register a callback;
  • Event::Active(event): Trigger from thread context;
  • Event::ActiveFromCallback(list, event): Trigger safely from ISR;
  • Event::GetList(event): Retrieve and cache event list;
  • Event::Bind(src, id_src, id_dst): Set up event bridging;
  • Internally uses RBTree<uint32_t> to manage event mappings, and LockFreeList to store callbacks.

Example: Test Event Binding and Triggering​

int arg = 0;
auto cb = Event::Callback::Create([](bool, int* a, uint32_t e) {
  *a += 1;
}, &arg);

Event e1, e2;
e1.Register(0x1234, cb);
e1.Active(0x1234);  // arg += 1
e2.Bind(e1, 0x4321, 0x1234);
e2.Active(0x4321);  // arg += 1

Application Scenarios​

  • Button/sensor interrupt event triggering;
  • State notification in multi-task cooperation;
  • Build event-message systems in combination with Topic/Message.

For more information, refer to the event.hpp source file.