maikel / glib-senders Goto Github PK

template <class... Senders>
auto for_each(Sender... senders) -> std::array<for-each-sender, sizeof...(Senders)>

This algorithm takes N senders and returns an array of N senders. Let std::array result = for_each(senders...) denote the returned array. The first element of result forwards the first completion, the second element forwards the second completion and so on.

If any sender of result is connected to a receiver, all input senders will be connected to intermediate receivers. If any operation is started, all intermediate operations will be started.

When all connected senders of result have completed, the outstanding operations are stopped.

Example:

• for_each gets 3 input senders and return and 3 output senders
• only 2 of 3 output senders are connected to a receiver
• when two operations complete the third operation will be stopped

I can not find any when_any algorithm in stdexec. A poor mans when_any could be something like this

template <typename... Senders> auto when_any(Senders&&... senders) {
  auto and_just_stopped = stdexec::let_value([](auto&&...) { return stdexec::just_stopped(); });
  return stdexec::when_all(
             (std::forward<Senders>(senders) | and_just_stopped)...) //
         | stdexec::upon_stopped([] {});;
}

But the resulting sender is not stoppable and it does not propagate any values.

I see at least two different behaviours:

1. Returns one sender. If any input senders completes with a value, then stop the other senders and propagate this one value to the next receiver.

2. Returns a range of senders

3. Returns a ManySender as in unifex

4. Returns an AsyncStream as in unifex

I like (4) most. But since (2-4) are out of scope I want to implement (1)

• when_any returns a sender and stops all other input senders upon completion
• when_any forwards any value, error or stop signal of the first operation that completes
• when_any is stoppable

The ::GSource*, which is the task interface of glib, is deallocated by glib. The destructor is currently called manually in the finalize callback in its vtable ::GSourceFunc.

Consider to implement a manual_life_time<T> wrapper to manage the life time of the Receiver object in schedule_operation.