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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3455) IPC.Client synchronisation looks weak
Date Wed, 04 Jun 2008 11:13:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12602244#action_12602244

Steve Loughran commented on HADOOP-3455:

> -1 tests included. 

A lot of the concurrency is going to be hard to test, because it is hard to replicate. What
we should be able to do is write a test case that triggers the NPE of HADOOP-3543 by having
the client fail to connect to a server and so attempt to clean up before out is set.

> IPC.Client synchronisation looks weak
> -------------------------------------
>                 Key: HADOOP-3455
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3455
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: ipc
>    Affects Versions: 0.18.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>         Attachments: hadoop-3455-updated.patch, hadoop-3455.patch
> Looking at HADOOP-3453 , its clear that Client.java is inconsistently synchronized
> 1. the running and shouldCloseConnection flags are not always read/written in synchronized
blocks, even though they are properties used to share information between threads. They should
be marked as volatile for access outside synchronized blocks, and all read-check-update operations
must be synchronized.
> 2. there are multiple calls to System.currentTimeMillis() in synchronized blocks; this
is a slow native operation and should ideally be done unsynchronized.
> 3. Synchronizing on the (out) stream is dangerous as its value changes during the life
of the class, and sometimes it is null. These blocks should all synchronize on the Client
> 4.  There are a number of places where InterruptedExceptions are caught and ignored in
a sleep-wait loop:
>      } catch (InterruptedException e) {
>       }
>    This isn't dangerous, but it does make the client harder to stop. These code fragments
should be looked at carefully.

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