* move shutdownfns, terminatefns and hammerfns out of separate goroutines
Coalesce the shutdownfns etc into a list of functions that get run at shutdown
rather then have them run at goroutines blocked on selects.
This may help reduce the background select/poll load in certain
configurations.
* The LevelDB queues can actually wait on empty instead of polling
Slight refactor to cause leveldb queues to wait on empty instead of polling.
* Shutdown the shadow level queue once it is empty
* Remove bytefifo additional goroutine for readToChan as it can just be run in run
* Remove additional removeWorkers goroutine for workers
* Simplify the AtShutdown and AtTerminate functions and add Channel Flusher
* Add shutdown flusher to CUQ
* move persistable channel shutdown stuff to Shutdown Fn
* Ensure that UPCQ has the correct config
* handle shutdown during the flushing
* reduce risk of race between zeroBoost and addWorkers
* prevent double shutdown
Signed-off-by: Andrew Thornton <art27@cantab.net>
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