Java Concurrency in Practice - Sample 14.12

the half-constructed-object is not visible to other threads

It is not true. The object is visible to other threads at the time of construction if it has any non final/volatile fields. Therefore, other threads might see a default value for permits i.e 0 which might not be consistent with the current thread.

The Java memory model offers a special guarantee of initialization safety for immutable objects (object with only final fields). An object reference visible to another thread does not necessarily mean that the state of that object is visible to the consuming thread - JCP $3.5.2

From Listing 3.15 of Java Concurrency in Practice:

While it may seem that field values set in a constructor are the first values written to those fields and therefore that there are no "older" values to see as stale values, the Object constructor first writes the default values to all fields before subclass constructors run. It is therefore possible to see the default value for a field as a stale value.