When using shouldSkipBlockingWait, do not grow the seen lock cache infinitely

Author: moshegood

src/main/java/com/amazonaws/services/dynamodbv2/AmazonDynamoDBLockClient.java

@@ -19,6 +19,7 @@
 import java.nio.ByteBuffer;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -234,6 +235,8 @@ public class AmazonDynamoDBLockClient implements Runnable, Closeable {
     private final String ownerName;
     private final ConcurrentHashMap<String, LockItem> locks;
     private final ConcurrentHashMap<String, LockItem> notMyLocks = new ConcurrentHashMap<>();
+    private final long maxCacheEntries = 100000;
+    private final List<String> notMyLocksList = Collections.synchronizedList(new ArrayList<>());
     private final ConcurrentHashMap<String, Thread> sessionMonitors;
     private final Optional<Thread> backgroundThread;
     private final Function<String, ThreadFactory> namedThreadCreator;
@@ -486,6 +489,12 @@ public LockItem acquireLock(final AcquireLockOptions options) throws LockNotGran
                           }
                         } else {
                             notMyLocks.put(id, existingLock.get());
+                            // Ensure we don't grow the cache too large.
+                            notMyLocksList.add(id);
+                            if (notMyLocks.size() > maxCacheEntries) {
+                                String oldest = notMyLocksList.remove(0);
+                                notMyLocks.remove(oldest);
+                            }
                         }
 
                         /*