[GOBBLIN-1207] Clear references to potentially large objects in Fork,…

[htran1]

… FileBasedExtractor, and HiveWritableHdfsDataWriter

Dear Gobblin maintainers,

Please accept this PR. I understand that it will not be reviewed until I have checked off all the steps below!

JIRA

• [1207] My PR addresses the following Gobblin JIRA issues and references them in the PR title. For example, "[GOBBLIN-XXX] My Gobblin PR"
  • https://issues.apache.org/jira/browse/GOBBLIN-1207

Description

• Here are some details about my PR, including screenshots (if applicable):
  Remove the reference to the underlying writer when HiveWritableHdfsDataWriter.close() is called.
  Remove the reference to the record iterator when the FileBasedExtractor is done with it.
  Add an option to close the Writer when the Fork is done.

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:
  ForkTest

Commits

• My commits all reference JIRA issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

[autumnust]

Overall LGTM

[autumnust]

The intention in this file doesn't seem to be right. Can you fix it ?

[htran1]

Fixed.

[autumnust]

+1 LGTM.