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hyper-util: legacy client pool IdleTask spins every pool_idle_timeout when pool is empty #4100
Description
Version
hyper-util 0.1.17, hyper 1.6.0
Platform
Linux 6.19.10 x86_64
Summary
I noticed that Deno's event loop continued spinning every pool idle timeout even after all connections were closed (see: denoland/deno#29444). I've tracked this down to hyper-util and have a proof of concept fix to cancel the IdleTask when the pool is empty here: hyperium/hyper-util#292.
(Sorry, I did not find the contribution guidelines until after filing the draft PR.)
Code Sample
$ DENO_LOG=hyper_util::client=trace deno run --allow-net 'data:,const client = Deno.createHttpClient({ poolIdleTimeout: 100 }); const res = await fetch("http:127.0.0.1:8000/", { client }); await res.bytes(); await new Promise(resolve=>setTimeout(resolve, 2000));'
TRACE RS - hyper_util::client::legacy::pool:679 - checkout waiting for idle connection: ("http", 127.0.0.1:8000)
TRACE RS - hyper_util::client::legacy::connect::http:482 - Http::connect; scheme=Some("http"), host=Some("127.0.0.1"), port=Some(Port(8000))
DEBUG RS - hyper_util::client::legacy::connect::http:768 - connecting to 127.0.0.1:8000
DEBUG RS - hyper_util::client::legacy::connect::http:771 - connected to 127.0.0.1:8000
TRACE RS - hyper_util::client::legacy::client:575 - http1 handshake complete, spawning background dispatcher task
TRACE RS - hyper_util::client::legacy::client:600 - waiting for connection to be ready
TRACE RS - hyper_util::client::legacy::client:610 - connection is ready
TRACE RS - hyper_util::client::legacy::pool:721 - checkout dropped for ("http", 127.0.0.1:8000)
TRACE RS - hyper_util::client::legacy::pool:348 - put; add idle connection for ("http", 127.0.0.1:8000)
DEBUG RS - hyper_util::client::legacy::pool:395 - pooling idle connection for ("http", 127.0.0.1:8000)
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:492 - idle interval evicting expired for ("http", 127.0.0.1:8000)
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:799 - idle interval checking for expired
TRACE RS - hyper_util::client::legacy::pool:810 - pool closed, canceling idle interval
Expected Behavior
When the client connection pool is empty the IdleTask should not wake the event loop.
Actual Behavior
IdleTask wakes the every pool_idle_timeout ms even when empty.
Additional Context
No response
Activity
Catwoman08 commentedon Aug 17, 2026
Thank you for your report. This looks like something we should fix.
Catwoman08 commentedon Aug 31, 2026
hyperium/hyper-util#292 fixes this issue.