[jira] [Created] (REEF-830) TreeTopology does not work correctly for certain task addition orders

["Gyeongin Yu (JIRA)" <ji...@apache.org>]

Gyeongin Yu created REEF-830:
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             Summary: TreeTopology does not work correctly for certain task addition orders
                 Key: REEF-830
                 URL: https://issues.apache.org/jira/browse/REEF-830
             Project: REEF
          Issue Type: Bug
          Components: REEF-IO
            Reporter: Gyeongin Yu
            Assignee: Gyeongin Yu


This issue is related to [REEF-817|https://issues.apache.org/jira/browse/REEF-817]. {{TreeTopology}} does not work correctly when the root task is added later than child tasks.

{{TreeTopology}} uses the {{prev}} field to track the lastly added leaf without considering that the root task might not be present yet. Thus if the root task is added later than others, {{TreeTopology.addTask}} sets {{prev}} as the root task before it exits, leading to incorrect sibling relations between nodes.

This bug can be reproduced by doing the following:
1. add two child tasks
2. add root task
3. add five child tasks

This was first found by [~chobrian].



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