Stream control and graceful shutdown

[vladimirvivien]

Currently, Automi implements a simplistic signal/control mechanism that implements a cascading close of channels when a predecessor component closes its output channel used as input by its successor. While this works in most cases, if a source closes its output while its successor operators are still processing.

Proposal - better stream control

This issue proposes stream control to be done using a combination of the followings:

• Injecting control marker items directly in the pipeline
• Centralized coordination via the stream orchestrator (implemented in the stream package)
• Status report by each node operator attached to the stream.