AVRO-2511: add case for sync

[clesaec]

What is the purpose of the change

AVRO-2511 :
DataFileWriter flush well data to disk only if using constructor with File, because it use internal class SyncableFileOutputStream, and writer activate "getFD().sync" in order to "Force all system buffers to synchronize with the underlying device".
Here, the idea is to do same when the DataFileWriter is initialized with FileOutputStream instance.
This does still not cover all cases; but at least, this one is ok.

Verifying this change

existing unit tests are enough.

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

[KalleOlaviNiemitalo]

Should the javadoc mention both Syncable and FileOutputStream?

[opwvhk]

Should the javadoc mention both Syncable and FileOutputStream?

Yes, I think it should.

[clesaec]

@KalleOlaviNiemitalo : A Javadoc on private field (line 62 of DataFileWriter) or elsewhere in the code ?

[KalleOlaviNiemitalo]

@clesaec, this one:

avro/lang/java/avro/src/main/java/org/apache/avro/file/DataFileWriter.java

Lines 441 to 448 in 73752a4

	/**
	* If this writer was instantiated using a File or using an
	* {@linkplain Syncable} instance, this method flushes all buffers for this
	* writer to disk. In other cases, this method behaves exactly like
	* {@linkplain #flush()}.
	*
	* @throws IOException
	*/

The existing text "using a File" seems to refer to public DataFileWriter<D> create(Schema schema, File file) and doesn't quite cover the case where public DataFileWriter<D> create(Schema schema, OutputStream outs) is called with outs being a FileOutputStream.

[clesaec]

the comment already mention Syncable :

  /**
    * If this writer was instantiated using a File or using an 
    * {@linkplain Syncable} instance

Should i write something like

    * If this writer was instantiated using a FileOutputStream or using an 
    * {@linkplain Syncable} instance

?

[KalleOlaviNiemitalo]

"using a File, FileOutputStream, or Syncable instance", I think. With hyperlinks to each type.

[clesaec]

Thanks, done.