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This PR is a first step to reducing a lot of the spinning-related issues that have cropped up. It does two things:
Context::wait_until
. There are already spin loops inrecv
/send
, so another set of spins after entering the park queue is excessive.Backoff::snooze
. As seen in crossbeam-channel uses pure userspace spinlocks, which perform very poorly in some situations #821 (comment), the amount ofPAUSE
instructions issued is quite high. This change reduces it from 6 to 3, similar to parking-lot. It also reduces the amount of total amount of spinning, reducingYIELD_LIMIT
to 6. This differs from parking-lot as it is common for a channel, unlike a mutex, to remain empty/full for long periods of times, and so if yielding doesn't allow progress after a few times it is likely better to park properly.