- Why is the callback method not called in T1?
This is usually not possible; if T1 is turned off while performing some other work, there is no way to return work to it if the stream already has no mechanism for publishing and a schedule for working on it (for example, the user interface stream through SynchronizationContext).
- Is there a standard template for cross-stream notification?
I would say no; There are several cross-thread synchronization patterns, each of which applies to different target scenarios.
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