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Date: Tue, 25 Oct 2016 09:41:58 +0000 (UTC)
From: "Tadayoshi Sato (JIRA)" <jira@apache.org>
To: issues@cxf.apache.org
Message-ID: <JIRA.13015023.1477388067000.77343.1477388518610@Atlassian.JIRA>
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Subject: [jira] [Comment Edited] (CXF-7109) ClientCallback may be invoked
 twice when Async HTTP Transport is used
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archived-at: Tue, 25 Oct 2016 09:42:05 -0000


    [ https://issues.apache.org/jira/browse/CXF-7109?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15604787#comment-15604787 ] 

Tadayoshi Sato edited comment on CXF-7109 at 10/25/16 9:41 AM:
---------------------------------------------------------------

I'm working on a pull req.

I think the best way to fix this issue is to remove the callback instance from the exchange once the callback's {{handle*****}} method is invoked so any other thread cannot invoke it again within the same exchange.


was (Author: tadayosi):
I'm working on a pull req.

> 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
>
> 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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