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From "James Clampffer (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-12427) libhdfs++: Prevent Requests from holding dangling pointer to RpcEngine
Date Wed, 13 Sep 2017 21:04:00 GMT

     [ https://issues.apache.org/jira/browse/HDFS-12427?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

James Clampffer updated HDFS-12427:
-----------------------------------
    Attachment: HDFS-12427.HDFS-8707.001.patch

New patch: RpcConnection was taking a weak_ptr and then calling lock() in the initializer
list to deference for member access.  Now it takes a shared_ptr to prevent a race between
initialization expression evaluation and RpcEngine destruction then demotes it to a weak_ptr
for longer term use.

> libhdfs++: Prevent Requests from holding dangling pointer to RpcEngine
> ----------------------------------------------------------------------
>
>                 Key: HDFS-12427
>                 URL: https://issues.apache.org/jira/browse/HDFS-12427
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs-client
>            Reporter: James Clampffer
>            Assignee: James Clampffer
>            Priority: Critical
>         Attachments: HDFS-12427.HDFS-8707.000.patch, HDFS-12427.HDFS-8707.001.patch
>
>
> The lifetime of Request objects is tied to the worker thread(s) in the async event loop.
 In the current code there's nothing that prevents a request from outliving the RpcEngine
(bound to FileSystem) while it's waiting for IO.  If the Request, or a task that makes a new
request, outlives the RpcEngine it attempts to dereference a dangling pointer and either crashes
or continues to run with bad data.
> Proposed fix is to reference count the RpcEngine via shared_ptr so that Requests can
hold a weak_ptr to it.  When a request or RpcConnection attempting to make a request needs
something from the RpcEngine like a call id number it can promote the weak_ptr to a shared_ptr.
 If it's unable to promote because the RpcEngine has been destroyed the Request's handler
can be invoked with an appropriate error message.  A weak_ptr must be used rather than a shared_ptr
to avoid reference cycles.



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