wasip2: Fix zero-wait pollables#13511
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This commit fixes an accidental bug introduced in bytecodealliance#13085 where repeatedly calling `ready()` on a zero-wait pollable in WASIp2 would never resolve. In bytecodealliance#13085 zero-length waits were updated to unconditionally yield to tokio to improve fairness, but this didn't take into account where the yield was repeatedly cancelled and never completed. The fix in this commit is to attempt the yield once and then never attempt it again. If the original yield is cancelled the next check on the pollable will go through. This is sort of a cancellation-safety fix where the previous implementation wasn't necessarily cancellation safe in the sense that repeatedly checking-and-cancelling never let anything progress, which is counterintuitive. Closes bytecodealliance#13507
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This commit fixes an accidental bug introduced in #13085 where repeatedly calling
ready()on a zero-wait pollable in WASIp2 would never resolve. In #13085 zero-length waits were updated to unconditionally yield to tokio to improve fairness, but this didn't take into account where the yield was repeatedly cancelled and never completed. The fix in this commit is to attempt the yield once and then never attempt it again. If the original yield is cancelled the next check on the pollable will go through. This is sort of a cancellation-safety fix where the previous implementation wasn't necessarily cancellation safe in the sense that repeatedly checking-and-cancelling never let anything progress, which is counterintuitive.Closes #13507