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From davidyan74 <...@git.apache.org>
Subject [GitHub] incubator-apex-core pull request: APEXCORE-60 Iteration support in...
Date Mon, 04 Jan 2016 19:14:31 GMT
Github user davidyan74 commented on a diff in the pull request:

    https://github.com/apache/incubator-apex-core/pull/185#discussion_r48768048
  
    --- Diff: api/src/main/java/com/datatorrent/api/Operator.java ---
    @@ -99,6 +99,25 @@ public String toString()
       }
     
       /**
    +   * DelayOperator is an operator of which the outgoing streaming window id is incremented
by *one* by the
    +   * engine, thus allowing loops in the "DAG". The output ports of a DelayOperator, if
connected, *must*
    +   * immediately connect to an upstream operator in the data flow path. Note that at
least one output port of
    +   * DelayOperator should be connected in order for the DelayOperator to serve its purpose.
    +   *
    +   * This is meant for iterative algorithms in the topology. A larger window increment
can be simulated by an
    +   * implementation of this interface.
    +   */
    +  interface DelayOperator extends Operator
    +  {
    +    /**
    +     * This method gets called at the first window of the execution.
    +     * The implementation is expected to emit tuples for initialization and/or
    +     * recovery.
    +     */
    +    void firstWindow();
    --- End diff --
    
    We concluded that the window id was not needed since the implementation could easily get
that by storing the window id as part of the checkpoint state.


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