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https://issues.apache.org/jira/browse/CXF-7109?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Freeman Fang reassigned CXF-7109:
---------------------------------
Assignee: Freeman Fang
> ClientCallback may be invoked twice when Async HTTP Transport is used
> ---------------------------------------------------------------------
>
> Key: CXF-7109
> URL: https://issues.apache.org/jira/browse/CXF-7109
> Project: CXF
> Issue Type: Bug
> Components: Core, Transports
> Affects Versions: 3.1.8
> Environment: RHEL 6.8
> Reporter: Tadayoshi Sato
> Assignee: Freeman Fang
>
> With Async HTTP Transport ({{cxf-rt-transports-http-hc}}) enabled, the
> {{ClientCallback}} object passed for the invocation of the client may be
> called twice when a failure occurs during the invocation:
> {code:java}
> Client client = ...
> client.invoke(new ClientCallback { ... }, opName, params);
> {code}
> At this moment, this issue is reproduced only on RHEL 6.8, but code analysis
> shows that it's a general multithreading issue with Async HTTP Transport and
> in theory it can happen on any platform.
> Here is what I've found with the code analysis:
> If for some reason the target endpoint is not reachable, this issue can
> happen when the callback for Apache HC {{HttpAsyncClient}} \[1] is invoked
> and thus shuts down {{SharedOutputBuffer}} earlier than {{HTTPConduit}} tries
> to write it before closing the conduit itself \[2].
> \[1]
> https://github.com/apache/cxf/blob/cxf-3.1.8/rt/transports/http-hc/src/main/java/org/apache/cxf/transport/http/asyncclient/AsyncHTTPConduit.java#L464
> \[2]
> https://github.com/apache/cxf/blob/cxf-3.1.8/rt/transports/http-hc/src/main/java/org/apache/cxf/transport/http/asyncclient/SharedOutputBuffer.java#L231
> When the above issue happens, the interceptor chain's fault observer is
> eventually invoked twice, once from the response workqueue thread \[3] that
> is spawn by the Apache HC {{HttpAsyncClient}} callback and the second time
> from the requesting thread at the interceptor chain \[4]; Thus the client
> callback is also invoked twice \[5]!
> \[3]
> https://github.com/apache/cxf/blob/cxf-3.1.8/rt/transports/http/src/main/java/org/apache/cxf/transport/http/HTTPConduit.java#L1177
> \[4]
> https://github.com/apache/cxf/blob/cxf-3.1.8/core/src/main/java/org/apache/cxf/phase/PhaseInterceptorChain.java#L366
> \[5]
> https://github.com/apache/cxf/blob/cxf-3.1.8/core/src/main/java/org/apache/cxf/interceptor/ClientOutFaultObserver.java#L59
> Why it happens so reliably only on RHEL 6.8 is still unclear (probably due to
> some thread scheduling logic specific to the kernel for RHEL 6.8), but since
> it's essentially an ordering issue for two distinct threads, in theory it can
> happen on any platforms. In general, CXF should really enforce that every
> client callback be invoked once and only once.
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