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https://issues.apache.org/jira/browse/CXF-8951?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Andriy Redko resolved CXF-8951.
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Resolution: Fixed
> Concurrent WebClient usage causes massive thread overhead
> ---------------------------------------------------------
>
> Key: CXF-8951
> URL: https://issues.apache.org/jira/browse/CXF-8951
> Project: CXF
> Issue Type: Bug
> Components: Core, JAX-RS
> Affects Versions: 3.6.2, 4.0.3, 3.6.3, 4.0.4
> Reporter: Lars Ködderitzsch
> Assignee: Andriy Redko
> Priority: Blocker
> Fix For: 4.0.5, 3.6.4
>
> Attachments: cxf-connector-threads.zip
>
>
> Concurrent usage of Webclients causes massively more threads to be created in
> cxf-3.6.x/4.x than before.
> Supposedly this results from introducing a new conduit implementation based
> on the "new" java http client compared to HttpUrlConnection before.
> It seems that a new http client is created per requesting thread - and each
> http client in turn creates an own pool of selector/worker threads.
> To demonstate I've attached a test project with several methods to test
> different scenarios.
> Each tests launches a simple JAX-RS Server, configures/uses WebClients in
> different configuration and submits 1000 requests via up to 100 parrallel
> requestor threads.
> The number of live threads in the JVM instance if printed after each request.
> Baseline is the number of threads used by the server instance + the 100
> requesting threads.
>
> singleClientInstanceWithNewConduit -> reuses a threadsafe client instance,
> thread count rises to 700+ live threads
> singleClientInstanceWithOldConduit -> reuses a threadsafe client instance,
> stays at about 200 threads
> clientPerRequestWithOldConduit -> creates a client instance per request
> (no closing!), keeps below 200 threads
> clientPerRequestWithNewConduit -> creates a client instance per request
> (no closing!), creates a runaway thread leak (!)
> clientPerRequestWithNewConduit is additionally interesting because current
> documentation is not clear about whether client instances
> are required to be resource managed or not.
> It appears that closing clients was not required up until cxf-3.6.0 and
> documentation actively encourages creating new "lightweight" client instances
> on the fly (see Thread safety in
> [https://cxf.apache.org/docs/jax-rs-client-api.html]).
> However, cxf-3.6+ implementation (and comments in CXF-8885) seem to suggest
> that clients are in fact *not lightweight* (anymore?) but need to be closed,
> when no longer used.
> But then in turn WebClient/Client does not even implement
> Closeable/Autoclosable. So, it's all quite muddy - and there doesn't seem to
> be a real consensus on the idiomatic usage of Webclients.
> It would be very nice if you could bring some clarity on this as well.
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