Member invoked by feed engine when a new processing thread is spawned.

Member is invoked by feed engine when processing thread is about to end.

Member is invoked by feed engine when feed engine's thread is idle. Thread becomes idle when either no data is received within time interval defined by FeedEngineSettings::dataWaitTime parameter or no pending data is available for processing. In the first case, callback is invoked with 'DataWaitTimeout' reason. In the second case, thread is considered as redundant and thus callback is invoked with 'Redundant' reason. After callback invocation threads may sleep in kernel to reduce load onto CPU and racing between feed engine working threads. thread is about to end.