The age action with flows creation could be supported on the multiple
threads. The age pools were created to manage the age resources, if
there is no room in the current pool then resize the age pool to the new
pool size and free the old one.
There's a race condition while one thread resizes the age pool and the
old pool resource be freed, and another thread query the age action
value of the old pool so the queried value is invalid.
This patch uses the read-write lock to protect the pool resource while
resizing and query.