并发和CacheLoader.load（）

Question

Should I synchronize the code in CacheLoader.load()?

I have code like this:

final Calculator calculator = new Calculator();

final LoadingCache<Key, Value> cache = CacheBuilder.newBuilder().build(new CacheLoader<Key, Value>(){
        @Override
        public Value load(final Key key) throws Exception {
            return calculator.calc(key);
        }} );

If the cache needs to load the values of two different keys from two different threads do I have to worry about thread interference in my Calculator object? Ie should I declare my Calculator.calc() method synchronized (or do something else to ensure thread-safety)?

Edit

Just so that it is clear I am asking specifically with regards to caching in Guava: http://code.google.com/p/guava-libraries/wiki/CachesExplained

Answer 1

The depends on the thread-safety of the action in the load method. It IS possible for it to be executed concurrently for different keys. Therefore if the action is not thread-safe, it should be made so in some way (synchronizing being the most trivial option).

So, if calculator.calc(key) is not thread-safe, synchronize it. If it is, don't.

Answer 2

If threads are going only to read, then you don't have to synchronize. If the threads are going to manipulate the value of the cache, then both read and write operations should be synchronized.

Answer 3

Thanks to everyone who answered.

I have checked this with a little test program and there IS thread interference. Specifically for different keys when the CacheLoader has to be invoked, these calls are not synchronized so if Calcualtor.calc() is not thread-safe, then weird results will ensue.