ConcurrentHashMap.sizeCtl vs HashMap.threshold, single-threaded, read by reflection
===================================================================================

new ConcurrentHashMap()          sizeCtl=0 table=null
after 1st put                    sizeCtl=12 table.length=16
after 12 puts (size=12)         sizeCtl=24 table.length=32
baseCount=12 counterCells=null size()=12 mappingCount()=12   (single thread: no CounterCell was ever needed)

Sizing constructors: ask for 32 and see what each map really allocates
new ConcurrentHashMap(32)        sizeCtl=64 (table not allocated yet)
  after 1st put                  sizeCtl=48 table.length=64
new HashMap(32)                  threshold=32 table=null (threshold holds the initial capacity until first put)
  after 1st put                  threshold=24 table.length=32

What sizeCtl holds while a resize is running (computed, not caught live):
resizeStamp(16)=32795  (rs << 16) + 2 = -2145714174  -> negative, so every other thread sees 'resize in progress'