source.Channel gets a nil value for stop channel

[mhrivnak]

Problem

When adding a Channel to a controller by calling Watch(), InjectStopChannel gets called with a value of nil instead of a real channel.

This appears to be because nothing sets the value of stop before Watch() gets called. The value of stop only gets set once the manager's Start() method is called.

Here's the order of operations:

1. Manager gets created
2. Controller gets created and added to the manager
3. Controller's Watch() method gets called with the new Channel as an argument
4. Manager's Start() method gets called, with a stop channel being passed in. This is the opportunity for a stop channel to be provided by a controller author.
5. The manager's Start() method calls each controller's Start() method, also passing through the stop channel.

At step 3, the manager's stop channel gets injected into the Channel. But the manager's stop channel doesn't get set until step 4, so at step 3 it has a nil value.

Workaround

The controller author can call InjectStopChannel directly and pass it the same channel they'll later pass to the manager's Start() method. But the InjectStopChannel method is clearly documented as not being intended for this purpose, nor is this approach helpful to the controller author.

[DirectXMan12]

duplicate of #103