Limit minimal time poll.Wait* functions can wait between attempts #2543
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Seems like this one needs an update linter from #2539 |
| @@ -91,7 +91,11 @@ func WaitWithBackoffWithRetries(ctx context.Context, b backoff.Backoff, numRetri | |||
| sleep := b.Duration() | |||
| if deadline, ok := ctx.Deadline(); ok { | |||
| ctxSleep := time.Until(deadline) | |||
| sleep = minDuration(sleep, ctxSleep) | |||
| // We want to wait for smaller of backoff sleep and context sleep | |||
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Question: IIUC from the PR description the <-t.C option is (often? always?) selected in the select block below when sleep is negative, is that the case?
If the deadline has passed, it seems that a sensible behavior would be to respect the context deadline by returning an error right away and thus not executing the operation.
It seems that with this change, ctx.Done(): is going to be selected below when the context has expired, independent of how large sleep is, so in that case, why not make sleep positive (strictly greater than 0)? Would that be sufficient?
Or even simpler, why not return with an error when ctxSleep <= 0 ?
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Essentially this is a race condition. If ctx already expired but did not perfom the cancel yet, so there's nothing in the ctx.Done() channel. At the same time if we have negative timer, t.C will always have a value in the channel.
Just means that positive sleep (in nanoseconds) doesn't really lets the context to finish in my tests.
We could just return a context.DeadlineExceeded error when ctxSleep <= 0, but then execution will continue in race with termination of the context. While technically correct (deadline did exceed), I don't know which consequences this might have.
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In the other hand additional 10ms of wait doesn't really add that much considering default backoff starts with 100ms and goes up from there (so context deadline in 10s of ms doesn't make much sense)
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pkg/poll/poll.go
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| // but it has to be over os scheduling interval | ||
| // otherwise context doesn't have time to finish |
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| // but it has to be over os scheduling interval | |
| // otherwise context doesn't have time to finish | |
| // but it has to be > 0 to give ctx.Done() a chance | |
| // to return below |
Currently calculation of sleep time can make it negative, which makes `t.C` channel return right away and does not give ctx time to finish on deadline. This means that even if context is expired, retries still happen until there are no more retries. The fix is to cap minimal sleep time at 5ms to make sure that context can perform expiration. NOTE: we could make the minimal sleep smaller, but it's wouldn't make sense getting less than OS scheduling frequency.
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Change Overview
Currently calculation of sleep time can make it negative, which makes
t.Cchannel return right away and does not give ctx time to finish on deadline.This means that even if context is expired, retries still happen until there are no more retries.
Currently it's causing test failures in
snapshot_test.goThe fix is to cap minimal sleep time at 5ms to make sure that context can perform expiration.
NOTE: we could make the minimal sleep smaller, but it's wouldn't make sense getting less than OS scheduling frequency.
Pull request type
Please check the type of change your PR introduces:
Test Plan
Added new test to
poll_test.go, but it's not always catching the race condition with context.