From d29a8d3ec141e02d3697d3a9a75574ec35384aaa Mon Sep 17 00:00:00 2001
From: Yannick Welsch <yannick@welsch.lu>
Date: Thu, 14 Oct 2021 10:08:20 +0200
Subject: [PATCH] Allow field usage tracker to be concurrent accessed (#79088)

While Lucene readers are currently only sequentially accessed, we expect future usages (and custom plugins) to access this concurrently.

Closes #78899
---
 .../search/stats/ShardFieldUsageTracker.java  | 26 ++++++++++---------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/index/search/stats/ShardFieldUsageTracker.java b/server/src/main/java/org/elasticsearch/index/search/stats/ShardFieldUsageTracker.java
index fc7d48db8f06f..ebac9f3e9d370 100644
--- a/server/src/main/java/org/elasticsearch/index/search/stats/ShardFieldUsageTracker.java
+++ b/server/src/main/java/org/elasticsearch/index/search/stats/ShardFieldUsageTracker.java
@@ -75,22 +75,24 @@ static class InternalFieldStats {
     }
 
     static class PerField {
-        boolean terms;
-        boolean postings;
-        boolean termFrequencies;
-        boolean positions;
-        boolean offsets;
-        boolean docValues;
-        boolean storedFields;
-        boolean norms;
-        boolean payloads;
-        boolean termVectors;
-        boolean points;
+        // while these fields are currently only sequentially accessed, we expect concurrent access by future usages (and custom plugins)
+        volatile boolean terms;
+        volatile boolean postings;
+        volatile boolean termFrequencies;
+        volatile boolean positions;
+        volatile boolean offsets;
+        volatile boolean docValues;
+        volatile boolean storedFields;
+        volatile boolean norms;
+        volatile boolean payloads;
+        volatile boolean termVectors;
+        volatile boolean points;
     }
 
     public class FieldUsageStatsTrackingSession implements FieldUsageNotifier, Releasable {
 
-        private final Map<String, PerField> usages = new HashMap<>();
+        // while this map is currently only sequentially accessed, we expect future usages (and custom plugins) to access this concurrently
+        private final Map<String, PerField> usages = new ConcurrentHashMap<>();
 
         @Override
         public void close() {