Re: Using a lot of Maps
On 22-11-2010 17:03, markspace wrote:
On 11/22/2010 1:54 PM, Lew wrote:
Or, it might see different values in
the 'hierarchy' and see the calculated,
Nope, the class as written is immutable, and therefore thread safe.
Technically it is not immutable as hashCode changes its state.
Absent some synchronization, all bets are off.
The "final" keyword synchronizes the writes in the constructor with all
reads that follow the constructor. The JLS specifies that the final
keyword creates a "freeze action" at the end of the constructor, which
synchronizes all writes in the constructor with all other possible reads
in the JVM.
The write of "hash" is idempotent and therefore safe. It's a race
condition, but not a data race.
If I had allowed "hierarchy" to be modified after the constructor, then
yes, I'd have to use some additional form of synchronization. However,
as the class stands, it's thread safe.
Safe, but not very elegant, because you have a test that
will make the calculation execute somewhere between one and
number of threads times.
Arne