[TESTS] There might be several live `BigArrays` instances at the same time.

src/test/java/org/elasticsearch/test/cache/recycler/MockBigArrays.java

@@ -31,8 +31,7 @@ import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.util.*;
 import org.elasticsearch.test.ElasticsearchTestCase;
 
-import java.util.Map;
-import java.util.Random;
+import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -45,8 +44,8 @@ public class MockBigArrays extends BigArrays {
      */
     private static final boolean TRACK_ALLOCATIONS = false;
 
-    private static volatile BigArrays INSTANCE = null;
-    private static ConcurrentMap<Object, Object> ACQUIRED_ARRAYS = new ConcurrentHashMap<>();
+    private static final Set<BigArrays> INSTANCES = Collections.synchronizedSet(Collections.newSetFromMap(new WeakHashMap<BigArrays, Boolean>()));
+    private static final ConcurrentMap<Object, Object> ACQUIRED_ARRAYS = new ConcurrentHashMap<>();
 
     public static void ensureAllArraysAreReleased() throws Exception {
         final Map<Object, Object> masterCopy = Maps.newHashMap(ACQUIRED_ARRAYS);
@@ -69,17 +68,17 @@ public class MockBigArrays extends BigArrays {
                 }
             }
         }
-        if (INSTANCE != null) {
+        for (final BigArrays bigArrays : INSTANCES) {
             // BigArrays are used on the network layer and the cluster is shared across tests so nodes might still be talking to
             // each other a bit after the test finished, wait a bit for things to stabilize if so
             final boolean sizeIsZero = ElasticsearchTestCase.awaitBusy(new Predicate<Object>() {
                 @Override
                 public boolean apply(Object input) {
-                    return INSTANCE.sizeInBytes() == 0;
+                    return bigArrays.sizeInBytes() == 0;
                 }
             });
             if (!sizeIsZero) {
-                final long sizeInBytes = INSTANCE.sizeInBytes();
+                final long sizeInBytes = bigArrays.sizeInBytes();
                 if (sizeInBytes != 0) {
                     throw new AssertionError("Expected 0 bytes, got " + sizeInBytes);
                 }
@@ -99,7 +98,7 @@ public class MockBigArrays extends BigArrays {
             seed = 0;
         }
         random = new Random(seed);
-        INSTANCE = this;
+        INSTANCES.add(this);
     }
 
     @Override