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Date: Tue, 4 Mar 2008 09:45:45 -0800 (PST)
From: "Tsz Wo (Nicholas), SZE (JIRA)" <jira@apache.org>
To: core-dev@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-2926) Ignoring IOExceptions on close
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    [ https://issues.apache.org/jira/browse/HADOOP-2926?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12575070#action_12575070 ] 

Tsz Wo (Nicholas), SZE commented on HADOOP-2926:
------------------------------------------------

> The standard idiom for multiple streams, as mentioned above, is nested try blocks
+1 Nested try blocks probably work in most situations.

However, it does not work when the number of streams is unknown in compile time, e.g.
{code}
OutputStream[] out = new OutputStream[n];
...
{code}
Also, it makes the code ugly when the number is large, say > 3.

> Ignoring IOExceptions on close
> ------------------------------
>
>                 Key: HADOOP-2926
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2926
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.16.0
>            Reporter: Owen O'Malley
>            Assignee: dhruba borthakur
>            Priority: Critical
>             Fix For: 0.16.1
>
>
> Currently in HDFS there are a lot of calls to IOUtils.closeStream that are from finally blocks. I'm worried that this can lead to data corruption in the file system. Take the first instance in DataNode.copyBlock: it writes the block and then calls closeStream on the output stream. If there is an error at the end of the file that is detected in the close, it will be *completely* ignored. Note that logging the error is not enough, the error should be thrown so that the client knows the failure happened.
> {code}
>    try {
>      file1.write(...);
>      file2.write(...);
>    } finally {
>       IOUtils.closeStream(file);
>   }
> {code}
> is *bad*. It must be rewritten as:
> {code}
>    try {
>      file1.write(...);
>      file2.write(...);
>      file1.close(...);
>      file2.close(...);
>    } catch (IOException ie) {
>      IOUtils.closeStream(file1);
>      IOUtils.closeStream(file2);
>      throw ie;
>    }
> {code}
> I also think that IOUtils.closeStream should be renamed IOUtils.cleanupFailedStream or something to make it clear it can only be used after the write operation has failed and is being cleaned up.

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