SafeBlocks if it's full Doesn't Block&Blocks, and deletes upon looking it up -Blocks, but doesn't delete when looking it up         8y4lmRjJ6OqEIHOJi0UtFbControl.Concurrent.STM.TMapMVarTMapMVar getTMapMVar newTMapMVarkeys peekElemsinsert insertForcelookup tryLookupobserve tryObservedeletegetTMVar