Support running generator on the manager

[shuds13]

This may be accomplished by one of the following approaches:

1. Run the generator serially (in-place) on the manager
2. Run the generator on a thread

Advantages for common use-case of a single generator:

• Simplifies determination of the number of workers
• Pass arguments by reference
• Reduces a communication

[jlnav]

Closed by recent release!