In State of Loom: part 2, there's a discussion about channels, and that Doug Lea had started working on a synchronous counterpart to Flow, called a Carrier.
That was back in May 2020, and Loom is now released. I can find no further mention of Carriers or channels or any similar mechanism anywhere. Does anyone know what happened to it? Did it get released and I just can't find it?! Is it still planned for some future Java version? Was it abandoned because LinkedTransferQueue was deemed sufficient?