HBASE-28804: Implement asynchronous retrieval of bucket-cache data from persistence (#6182) (#6219)

The cherry-pick of HBASE-29727 into branch-2.6 accidently brought most of HBASE-28804 into branch-2, this is to backport the remaining original change in HBASE-28804.

Signed-off-by: Wellington Chevreuil <wchevreuil@apache.org>
Change-Id: I816141ccebf91191aaa4cb6afa04343b64663eb0

Author: jhungund

hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/HFilePreadReader.java

@@ -37,6 +37,9 @@ public class HFilePreadReader extends HFileReaderImpl {
   public HFilePreadReader(ReaderContext context, HFileInfo fileInfo, CacheConfig cacheConf,
     Configuration conf) throws IOException {
     super(context, fileInfo, cacheConf, conf);
+    cacheConf.getBlockCache()
+      .ifPresent(cache -> cache.waitForCacheInitialization(WAIT_TIME_FOR_CACHE_INITIALIZATION));
+
     // Initialize HFileInfo object with metadata for caching decisions
     fileInfo.initMetaAndIndex(this);
     // master hosted regions, like the master procedures store wouldn't have a block cache