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Get rid of time.After in for loops #6303

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merged 1 commit into from
Sep 25, 2024
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@Shaddoll Shaddoll commented Sep 24, 2024

What changed?
Replace time.After in for loops with NewTimer + Reset or Sleep

Why?
before go 1.23, time.After in for loops can use a lot of memory if the timeout is too long and don't expire.
after go 1.23, time.After does allocation a lot in for loops.
NewTimer + Reset gets rid of this problem.

How did you test it?
existing unit tests

Potential risks

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Documentation Changes

@Shaddoll Shaddoll changed the title Replace time.After in for loops with NewTimer + Reset Get rid of time.After in for loops Sep 24, 2024
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codecov bot commented Sep 24, 2024

Codecov Report

Attention: Patch coverage is 47.82609% with 12 lines in your changes missing coverage. Please review.

Project coverage is 73.20%. Comparing base (11c3626) to head (a64f23c).
Report is 3 commits behind head on master.

Files with missing lines Patch % Lines
service/history/queue/timer_queue_processor.go 0.00% 7 Missing ⚠️
service/history/queue/transfer_queue_processor.go 28.57% 4 Missing and 1 partial ⚠️
Additional details and impacted files
Files with missing lines Coverage Δ
common/cache/metricsScopeCache.go 89.47% <100.00%> (+0.58%) ⬆️
...ervice/history/engine/engineimpl/query_workflow.go 50.73% <100.00%> (ø)
service/worker/scanner/tasklist/scavenger.go 80.35% <100.00%> (+0.54%) ⬆️
service/history/queue/transfer_queue_processor.go 35.38% <28.57%> (-0.04%) ⬇️
service/history/queue/timer_queue_processor.go 24.08% <0.00%> (-0.50%) ⬇️

... and 7 files with indirect coverage changes


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I got curious and dug around in how timers are created and scheduled, to see what the initial-0 would do, because I hadn't seen that pattern before.

Looks like it puts it into the timer heap, sorts it, and it fires ~immediately, so it's safe both before and after 1.23, though slightly wasteful (but it's a one-time tiny cost so it seems fine to ignore it).

1.23 is substantially more complex, but seems to be essentially the same. And probably has some optimizations for immediate-firing, given how the blog post talks about it more-reliably following both branches with very small delays. So safe and no worse + probably better there too 👍


Since this very nearly gets rid of ALL of our time.After use, yea, I think the minor added complexity is fine. It's a better habit for us to be in, since we have a significant amount of fast + perpetual loops, and we can almost just ban After now to prevent a costly leak from sneaking back in.

Check the ticker instances, since they seem kinda straightforward to me? Otherwise LGTM and seems fine either way.

service/worker/scanner/tasklist/scavenger.go Outdated Show resolved Hide resolved
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@Shaddoll Shaddoll merged commit 16c5e64 into cadence-workflow:master Sep 25, 2024
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@Shaddoll Shaddoll deleted the timer branch September 25, 2024 16:47
dkrotx pushed a commit to dkrotx/cadence that referenced this pull request Sep 26, 2024
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3 participants