It would be good to formalize the design of kernels and the controlling query execution layer (e.g. volcano batch model?) to understand the following:

Contracts for kernels:

• Thread safety of kernels?

• When Kernels should allocate memory vs expect preallocated memory?  How to communicate requirements for a kernels memory allocaiton?

• How to communicate the whether a kernels execution is parallelizable across a ChunkedArray?  How to determine if the order to execution across a ChunkedArray is important?

• How to communicate when it is safe to re-use the same buffers and input and output to the same kernel?

  What does the threading model look like for the higher level of control?  Where should synchronization happen?

Reporter: Micah Kornfield / @emkornfield

Related issues:

• [C++] C++ array kernels framework and execution buildout (umbrella issue) (relates to)

_{Note: This issue was originally created as ARROW-4333. Please see the migration documentation for further details.}