Interface for specifying parallel operation over DLists. The semantics
of DoFn lifecycle are as follows:
For a given chunk of DList elements:
1. 'setup' will be called;
2. 'process' will be called for each element in the chunk;
3. 'cleanup' will be called.
These 3 steps encapsulate the entire life-cycle of a DoFn. A DoFn object
will not be referenced after these steps
Interface for specifying parallel operation over DLists. The semantics of DoFn lifecycle are as follows:
For a given chunk of DList elements: 1. 'setup' will be called; 2. 'process' will be called for each element in the chunk; 3. 'cleanup' will be called.
These 3 steps encapsulate the entire life-cycle of a DoFn. A DoFn object will not be referenced after these steps