A polymorphic hashtbl that uses Pool to avoid allocation.
This uses the standard linked-chain hashtable algorithm, albeit with links performed
through a pool and hence avoiding caml_modify (for table manipulation), even when
hashing object keys/values.
This implementation is worth exploring for your application if profiling demonstrates
that garbage collection and the caml_modify write barrier are a significant part of
your execution time.
resize t size ensures that t can hold at least size entries without resizing
(again), provided that t has growth enabled. This is useful for sizing global
tables during application initialization, to avoid subsequent, expensive growth
online. See [root:Jane_parachute].Immediate.String.resize, for example.
on_grow ~before ~after allows you to connect higher level loggers to the point where
these hashtbls grow. before is called before the table grows, and after after it.
This permits you to e.g. measure the time elapsed between the two.
This is only meant for debugging and profiling, e.g. note that once a callback is installed, there is no way to remove it.