From fc4a1d96ae12908acb0fc01164dbe52b6d4c16a0 Mon Sep 17 00:00:00 2001
From: Yannick Welsch <yannick@welsch.lu>
Date: Thu, 17 Jan 2019 19:18:47 +0100
Subject: [PATCH] Fix assertion at end of forceRefreshes (#37559)

This commit ensures that we only change refreshListeners to a list if we're actually adding
something to the list.
---
 .../index/shard/RefreshListeners.java           | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/server/src/main/java/org/elasticsearch/index/shard/RefreshListeners.java b/server/src/main/java/org/elasticsearch/index/shard/RefreshListeners.java
index b4b9e13f7e063..713563eb111ba 100644
--- a/server/src/main/java/org/elasticsearch/index/shard/RefreshListeners.java
+++ b/server/src/main/java/org/elasticsearch/index/shard/RefreshListeners.java
@@ -129,15 +129,12 @@ public boolean addOrNotify(Translog.Location location, Consumer<Boolean> listene
             return true;
         }
         synchronized (this) {
-            List<Tuple<Translog.Location, Consumer<Boolean>>> listeners = refreshListeners;
-            if (listeners == null) {
-                if (closed) {
-                    throw new IllegalStateException("can't wait for refresh on a closed index");
-                }
-                listeners = new ArrayList<>();
-                refreshListeners = listeners;
+            if (closed) {
+                throw new IllegalStateException("can't wait for refresh on a closed index");
             }
-            if (refreshForcers == 0 && listeners.size() < getMaxRefreshListeners.getAsInt()) {
+            List<Tuple<Translog.Location, Consumer<Boolean>>> listeners = refreshListeners;
+            final int maxRefreshes = getMaxRefreshListeners.getAsInt();
+            if (refreshForcers == 0 && maxRefreshes > 0 && (listeners == null || listeners.size() < maxRefreshes)) {
                 ThreadContext.StoredContext storedContext = threadContext.newStoredContext(true);
                 Consumer<Boolean> contextPreservingListener = forced -> {
                     try (ThreadContext.StoredContext ignore = threadContext.stashContext()) {
@@ -145,8 +142,12 @@ public boolean addOrNotify(Translog.Location location, Consumer<Boolean> listene
                         listener.accept(forced);
                     }
                 };
+                if (listeners == null) {
+                    listeners = new ArrayList<>();
+                }
                 // We have a free slot so register the listener
                 listeners.add(new Tuple<>(location, contextPreservingListener));
+                refreshListeners = listeners;
                 return false;
             }
         }