[jira] [Commented] (HADOOP-15429) unsynchronized index causes DataInputByteBuffer$Buffer.read hangs

["Chris Douglas (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-15429?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16458852#comment-16458852 ] 

Chris Douglas commented on HADOOP-15429:
----------------------------------------

{{DataInputByteBuffer}} is not threadsafe. What is the use case?

> unsynchronized index causes DataInputByteBuffer$Buffer.read hangs
> -----------------------------------------------------------------
>
>                 Key: HADOOP-15429
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15429
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: io
>    Affects Versions: 0.23.0
>            Reporter: John Doe
>            Priority: Minor
>
> In DataInputByteBuffer$Buffer class, the fields bidx and buffers, etc are unsynchronized when used in read() and reset() function. In certain circumstances, e.g., the reset() is invoked in a loop, the unsynchronized bidx and buffers can trigger a concurrency bug.
> Here is the code snippet.
> {code:java}
>     ByteBuffer[] buffers = new ByteBuffer[0];
>     int bidx, pos, length;
>     @Override
>     public int read(byte[] b, int off, int len) {
>       if (bidx >= buffers.length) {
>         return -1;
>       }
>       int cur = 0;
>       do {
>         int rem = Math.min(len, buffers[bidx].remaining());
>         buffers[bidx].get(b, off, rem);
>         cur += rem;
>         off += rem;
>         len -= rem;
>       } while (len > 0 && ++bidx < buffers.length); //bidx is unsynchronized
>       pos += cur;
>       return cur;
>     }
>     public void reset(ByteBuffer[] buffers) {//if one thread keeps calling reset() in a loop
>       bidx = pos = length = 0;
>       this.buffers = buffers;
>       for (ByteBuffer b : buffers) {
>         length += b.remaining();
>       }
>     }
> {code}



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