Guava cache - How can I download all the missing ones?

Question

I have a use case when the method of loading cache data is a mass call, but I will never use getAll to get data from the cache. Is there a way for multiple concurrent all to block on one loadAll? I don’t want individuals on different keys to make multiple calls to the data source.

cache.get(key1); // missing entry, starts refresh cache.get(key2); // separate thread, already getting reloaded due to key1 miss 

I think that I will have to implement my own synchronization after searching in LocalCache, using something like a local cache in my data accessory, which allows you to call only after so many units of time. When the call is made, update the local copy with a single assignment statement.

Am I missing something from the Guava cache library?

Edit:

I am considering something like the following. However, it can continue to return stale data, and loadAll ends. I would prefer all the blocks in load , and only the first request calls loadAll to continue.

 public class DataCacheLoader extends CacheLoader<String, Double> { private final Cache<String, Double> cache; private ConcurrentMap<String, Double> currentData; private final AtomicBoolean isloading; public DataCacheLoader( final Cache<String, Double> cache ) { this.cache = cache; isLoading = new AtomicBoolean( false ); } @Override public Double load( final String key ) throws Exception { if ( isLoading.compareAndSet( false, true ) ) { cache.putAll( loadAll( Lists.newArrayList( key ) ) ) ); } return currentData.get( key ); } @Override public Map<String, Double> loadAll(Iterable<? extends String> keys) throws Exception { currentData = source.getAllData(); return currentData; } } 

Answer 1

Here is the solution that should do the trick. The idea is that instead of caching each individual key, you cache the entire card with one fixed key. The only drawback is that you won’t be able to skip parts of the base map (at least not so easily), but this may not be a requirement.

 class MyCache { private static final Object KEY = new Object(); private final LoadingCache<Object, Map<String, Double>> delegate = new CacheBuilder() // configure cache .build(new CacheLoader<Object, Map<String, Double>>() { public Map<String, Double> load(Object key) { return source.load(); } }; double get(String key) { return cache.get(KEY).get(key); } }