Adding comments for metric and Todo works

amazon-kinesis-client/src/main/java/software/amazon/kinesis/coordinator/Scheduler.java

@@ -375,6 +375,9 @@ public class Scheduler implements Runnable {
 
     private void waitUntilHashRangeCovered() throws InterruptedException {
 
+        // TODO: Currently this call is not in use. We may need to implement this method later. Created SIM to track the work: https://sim.amazon.com/issues/KinesisLTR-202
+        // TODO: For future implementation, streamToShardSyncTaskManagerMap might not contain the most up to date snapshot of active streams.
+        // Should use currentStreamConfigMap to determine the streams to check.
         while (!leaderElectedPeriodicShardSyncManager.hashRangeCovered()) {
             // wait until entire hash range is covered
             log.info("Hash range is not covered yet. Checking again in {} ms", HASH_RANGE_COVERAGE_CHECK_FREQUENCY_MILLIS);

amazon-kinesis-client/src/main/java/software/amazon/kinesis/leases/ShardSyncTask.java

@@ -76,6 +76,9 @@ public class ShardSyncTask implements ConsumerTask {
             exception = e;
             shardSyncSuccess = false;
         } finally {
+            // NOTE: This metric is reflecting if a shard sync task succeeds. Customer can use this metric to monitor if
+            // their application encounter any shard sync failures. This metric can help to detect potential shard stuck issues
+            // that are due to shard sync failures.
             MetricsUtil.addSuccess(scope, "SyncShards", shardSyncSuccess, MetricsLevel.DETAILED);
             MetricsUtil.endScope(scope);
         }