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From "Haohui Mai (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-9265) InputStreamImpl should hold a shared_ptr of the BlockReader
Date Wed, 21 Oct 2015 18:50:27 GMT

     [ https://issues.apache.org/jira/browse/HDFS-9265?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

Haohui Mai updated HDFS-9265:
       Resolution: Fixed
     Hadoop Flags: Reviewed
    Fix Version/s: HDFS-8707
           Status: Resolved  (was: Patch Available)

I've committed the patch to the HDFS-8707 branch. Thanks [~James Clampffer] for the contribution.

> InputStreamImpl should hold a shared_ptr of the BlockReader
> -----------------------------------------------------------
>                 Key: HDFS-9265
>                 URL: https://issues.apache.org/jira/browse/HDFS-9265
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs-client
>            Reporter: James Clampffer
>            Assignee: James Clampffer
>            Priority: Blocker
>             Fix For: HDFS-8707
>         Attachments: HDFS-9265.HDFS-8707.000.patch
> The remote block reader relies on undefined behavior in how it uses enable_shared_from_this.
> http://en.cppreference.com/w/cpp/memory/enable_shared_from_this
> The spec states a shared_ptr to an object inheriting from enable_shared_from_this must
be live before calling make_shared_from_this.  
> Calling make_shared_from_this without an existing shared_ptr is undefined behavior and
causes deterministic crashes when the code is built with GCC.
> example:
> class foo : public enable_shared_from_this {/*bar*/};
> safe:
> auto ptr1 = std::make_shared<foo>();
> auto ptr2 = foo->make_shared_from_this();
> broken:
> foo *ptr = new foo();
> auto ptr2 = foo->make_shared_from_this(); //no existing live shared_ptr
> In order to fix the input stream should call std::make_shared and hang onto a shared_ptr
to the block reader.  The block reader will then be free to call make_shared_from this as
much as it wants without issue.  

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