Releases

v2.17.0

• Introduce Async::Queue#push and Async::Queue#pop for compatibility with ::Queue.

v2.16.0

Better Handling of Async and Sync in Nested Fibers

Interleaving bare fibers within Async and Sync blocks should not cause problems, but it presents a number of issues in the current implementation. Tracking the parent-child relationship between tasks, when they are interleaved with bare fibers, is difficult. The current implementation assumes that if there is no parent task, then it should create a new reactor. This is not always the case, as the parent task might not be visible due to nested Fibers. As a result, Async will create a new reactor, trying to stop the existing one, causing major internal consistency issues.

I encountered this issue when trying to use Async within a streaming response in Rails. The protocol-rack uses a normal fiber to wrap streaming responses, and if you try to use Async within it, it will create a new reactor, causing the server to lock up.

Ideally, Async and Sync helpers should work when any Fiber.scheduler is defined. Right now, it's unrealistic to expect Async::Task to work in any scheduler, but at the very least, the following should work:

reactor = Async::Reactor.new # internally calls Fiber.set_scheduler

# This should run in the above reactor, rather than creating a new one.
Async do
  puts "Hello World"
end

In order to do this, bare Async and Sync blocks should use Fiber.scheduler as a parent if possible.

See https://github.com/socketry/async/pull/340 for more details.