Package groovy.concurrent

Class ChannelSelect.Offer

java.lang.Object
groovy.concurrent.ChannelSelect.Offer
Enclosing class:
ChannelSelect
public static final class ChannelSelect.Offer extends Object
One branch of a select: an input guard created by ChannelSelect.receive(AsyncChannel), an output guard created by ChannelSelect.send(AsyncChannel, Object), or a timeout created by ChannelSelect.after(long). Immutable and freely reusable across selects.
Since:
6.0.0

  • Method Details

    • when

      public ChannelSelect.Offer when(BooleanSupplier condition)
      Returns a copy of this offer guarded by condition: the precondition written onto the branch itself, as occam, Ada, Erlang and Kotlin write it, rather than passed positionally to ChannelSelect.select(boolean...). 
      
 def sel = offers(receive(input).when { size < capacity },
                  receive(request).when { size > 0 })
 def result = await sel.select()

      The condition is evaluated afresh on every ChannelSelect.select() call — that is why it is a supplier and not a boolean — so one guarded select may be held and reused as the state it guards on changes. When it does not hold, the offer is not registered on its channel: nothing is taken from it and nothing is sent to it, and the remaining offers keep their positions, so ChannelSelect.Result.getIndex() denotes the same branch either way.

      Guards conjoin: over a second when both conditions must hold, as must the corresponding flag of a ChannelSelect.select(boolean...) call. If no offer of a select is enabled the result fails with IllegalStateException, since there is nothing left to wait for.

      Parameters:
      condition - the guard, consulted once per select
      Returns:
      a guarded copy of this offer
      Since:
      6.0.0