anchor.diff:  
   The JavaDoc about the link:{cache2k_docs}/apidocs/cache2k-api/index.html?org/cache2k/io/AdvancedCacheLoader.html[`AdvancedCacheLoader`]
   contains additional details.
  +
  +=== Asynchronous Loader and Bulk Loader
  +
  +The additional interface variants `AsyncCacheLoader` and `AsyncBulkCacheLoader` are available to
  +implement more efficient loaders. When using the bulk loader and refresh ahead a
  +`CoalescingBulkLoader` is can be used to combine single refresh ahead requests into one bulk
  +request.
  +
  +=== Concurrent Load Requests
  +
  +A `Cache.get` or `Cache.getAll` will start a load and wait until the load is completed and return
  +the result. With `Cache.loadAll` and `Cache.reloadAll` it is possible to start a concurrent
  +load operation and get notified upon completion. If the configured loader does not support
  +async operation, a thread pool (defined by `loaderExecutor`) will be used for the concurrent
  +operation.
   
   === Invalidating
   
  
positive.code: 
  === Defining a Loader
  
  A loader is defined by implementing the abstract class `CacheLoader`.
  See the <<getting-started,Getting Started>> example about read through.
  
  [source,java]
  
negative.code: `Cache.containsKey` will not return true when the value exists in the system of authority,
  but only reflects the cache state.
  
  To prevent pitfalls a reduced interface is available: {api_link}/KeyValueSource.html[`KeyValueSource`].
  