It should be faster, even when
is equal to one,
for thread_alloc to hold onto memory.
equal to true,
instructs thread_alloc to hold onto memory,
and put it in the available
after each call to return_memory
thread_alloc with hold onto memory for future quick use.
If it is false, future calls to return_memory
will return the corresponding memory to the system.
By default (when hold_memory has not been called)
thread_alloc does not hold onto memory.
Memory that is being held by thread_alloc can be returned
to the system using free_available
Input File: cppad/utility/thread_alloc.hpp