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From "Colin Patrick McCabe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-8491) We need to check for short writes when using FileChannel#write and related methods
Date Thu, 07 Jun 2012 18:44:23 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-8491?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13291199#comment-13291199
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Colin Patrick McCabe commented on HADOOP-8491:
----------------------------------------------

I re-read the documents, and I'm no longer so sure about this one.

The documentation for WritableByteChannel#write says:
{quote}
Writes a sequence of bytes to this channel from the given buffer.

An attempt is made to write up to r bytes to the channel, where r is the number of bytes remaining
in the buffer, that is, src.remaining(), at the moment this method is invoked.

Suppose that a byte sequence of length n is written, where 0 <= n <= r. This byte sequence
will be transferred from the buffer starting at index p, where p is the buffer's position
at the moment this method is invoked; the index of the last byte written will be p + n - 1.
Upon return the buffer's position will be equal to p + n; its limit will not have changed.

Unless otherwise specified, a write operation will return only after writing all of the r
requested bytes. Some types of channels, depending upon their state, may write only some of
the bytes or possibly none at all. A socket channel in non-blocking mode, for example, cannot
write any more bytes than are free in the socket's output buffer.

This method may be invoked at any time. If another thread has already initiated a write operation
upon this channel, however, then an invocation of this method will block until the first operation
is complete. 
{quote}

Notice the key sentence here: *Unless otherwise specified, a write operation will return only
after writing all of the r requested bytes.*

Then the documentation for FileChannel#write says:
{quote}
Writes a sequence of bytes to this channel from the given buffer.

Bytes are written starting at this channel's current file position unless the channel is in
append mode, in which case the position is first advanced to the end of the file. The file
is grown, if necessary, to accommodate the written bytes, and then the file position is updated
with the number of bytes actually written. Otherwise this method behaves exactly as specified
by the WritableByteChannel interface. 
{quote}

I don't see it "otherwise specified" here, so in essence, write should be equivalent to writeFully
for FileChannel (but not for certain other subclasses of WritableByteChannel.)  Or am I missing
something?
                
> We need to check for short writes when using FileChannel#write and related methods
> ----------------------------------------------------------------------------------
>
>                 Key: HADOOP-8491
>                 URL: https://issues.apache.org/jira/browse/HADOOP-8491
>             Project: Hadoop Common
>          Issue Type: Bug
>            Reporter: Colin Patrick McCabe
>            Assignee: Colin Patrick McCabe
>            Priority: Minor
>
> We need to check for short writes when using WritableByteChannel#write and related methods.

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