[infinispan-issues] [JBoss JIRA] (ISPN-6279) Refactor CacheLoader API to make it thread safe

[Dan Berindei (JIRA)]

    [ https://issues.jboss.org/browse/ISPN-6279?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13169920#comment-13169920 ] 

Dan Berindei commented on ISPN-6279:
------------------------------------

I think forcing the cache loader to implement the iteration of the keys via a lambda would only complicate the loader implementation, with no concrete advantage for the callers.

If a caller doesn't want to deal with concurrency issues, the solution is easy: just pass in a {{WithinThreadExecutor}} instance.

> Refactor CacheLoader API to make it thread safe
> -----------------------------------------------
>
>                 Key: ISPN-6279
>                 URL: https://issues.jboss.org/browse/ISPN-6279
>             Project: Infinispan
>          Issue Type: Feature Request
>          Components: Loaders and Stores
>            Reporter: Sebastian Łaskawiec
>            Priority: Minor
>             Fix For: 9.0.0.Final
>
>
> h3. Introduction
> Currently {{CacheLoader}} thread safety can be easily compromised by broken implementations. We should provide a better implementation to make it more convenient and less error prone.
> h3. Problem statement
> CacheLoader API looks like this:
> {code}
> public interface AdvancedCacheLoader<K, V> extends CacheLoader<K, V> {
> ...
>    void process(KeyFilter<? super K> filter, CacheLoaderTask<K, V> task, Executor executor, boolean fetchValue, boolean fetchMetadata);
> ...
> }
> {code}
> The CacheLoader implementation controls {{CacheLoaderTask}} as well as the number of threads used for processing (specified by {{Executor}}). If one wants to collect all keys (similarly to [AdvancedCacheLoader|https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/persistence/spi/AdvancedCacheLoader.java]) it is very easy to hit concurrently issues while adding them to the set (See previous JIRAs: ISPN-3938 and ISPN-6276). 
> h3. Solution
> The solution should take away currently control (Executor) and keyset (the simplest idea is to add it to {{CacheLoaderTask}}) from from the implementation. One of the ideas is to create a Lambda expression for pulling records from Cache Store. Note that similar changes will need to be performed to {{CacheWriter}} (to make it similar).



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