async/scope.hpp

#include <async/scope.hpp>

dynamic_scope and dynamic_deferred_scope are operations that run a number of senders concurrently, where the number is only known at runtime. The senders are supplied by a fill function, and the operation only completes once the fill function has returned and all of the senders have completed.

Prototype

template<typename Sender, typename Allocator, typename Fill>
sender dynamic_scope(Allocator allocator, Fill fill); // (1)

template<typename Sender, typename Allocator, typename Fill>
sender dynamic_deferred_scope(Allocator allocator, Fill fill); // (2)

1. Calls fill(spawn). Each call to spawn(sender) starts sender immediately.
2. Calls fill(spawn). The senders passed to spawn() are only started after fill returns.

Requirements

Sender is a sender that doesn't return any value. Fill is invocable with a reference to a callable that takes a Sender.

spawn() may only be called from within fill, on the thread that runs fill. It must not be called after fill returns and it must not be called concurrently.

Arguments

• allocator - the allocator used to allocate the state of each sender.
• fill - the function that supplies the senders.

Return value

This function returns a sender of unspecified type. The sender does not return any value.

The senders passed to spawn() are started with the environment of the receiver that the returned sender is connected to.

With (1), a sender may already have completed by the time that spawn() returns. (2) guarantees that no sender runs before fill returns. This is useful if fill runs in a context that the senders must not run in (e.g., while a lock is held).

Examples

async::run(async::dynamic_deferred_scope<async::result<void>>(frg::stl_allocator{},
	[] (auto &spawn) {
		for(int i = 0; i < 3; i++) {
			spawn([] (int i) -> async::result<void> {
				std::cout << "Hi " << i << std::endl;
				co_return;
			}(i));
			std::cout << "Spawned " << i << std::endl;
		}
	}
));
std::cout << "Done" << std::endl;

Output:

Spawned 0
Spawned 1
Spawned 2
Hi 0
Hi 1
Hi 2
Done