Observation of slow task execution is performed when scheduling more work to avoid the overhead of another thread or timer checking on tasks. This results in lower overhead but means that slow running tasks may not be observed while executing. However, they will trigger a callback to the slowTaskCompleted regardless of whether additional work is scheduled.

This makes assumptions that the underlying Timer will execute tasks sequentially in order to catch slow running tasks during execution. If the underlying Timer executes tasks in parallel the callback slowTaskExecuting will become unreliable. However, the slowTaskCompleted callback will remain reliable but must be a thread-safe implementation.