boost::capy::async_event

An asynchronous event for coroutines.

Synopsis

Declared in <boost/capy/ex/async_event.hpp>

class async_event;

Description

This event provides a way to notify multiple coroutines that some condition has occurred. When a coroutine awaits an unset event, it suspends and is added to a wait queue. When the event is set, all waiting coroutines are resumed.

Cancellation

When a coroutine is suspended waiting for the event and its stop token is triggered, the waiter completes with error::canceled instead of waiting for set().

Cancellation only applies while the coroutine is suspended in the wait queue. If the event is already set when wait() is called, the wait completes immediately even if the stop token is already signaled.

Zero Allocation

No heap allocation occurs for wait operations.

Thread Safety

The event operations are designed for single‐threaded use on one executor. The stop callback may fire from any thread.

Example

async_event event;

task<> waiter() {
    auto [ec] = co_await event.wait();
    if(ec)
        co_return;
    // ... event was set ...
}

task<> notifier() {
    // ... do some work ...
    event.set();  // Wake all waiters
}