Memory leak with Mongo Java Connection with POJO cause OOM

String dbURI = "mongodb://mongoji:pass@XXXX:27017,xxxx:27017,xxxx:27017/admin?replicaSet=rs0";
    MongoClient mongoClient = new MongoClient(new MongoClientURI(dbURI));
    DB db = mongoClient.getDB("test");
    DBCollection collection = db.getCollection("read");
BasicDBObject data = new BasicDBObject();
    data.append("DT", now.getTime());
collection.insert(data);
DBCollection collection2 = db.getCollection("sent");
BasicDBObject searchQuery = new BasicDBObject();
List<BasicDBObject> list = new ArrayList<BasicDBObject>();
list.add(new BasicDBObject("email", email));
list.add(new BasicDBObject("email2", email));// multiple

searchQuery.put("$and", list);
BasicDBObject newDocument = new BasicDBObject();
newDocument.append("$set", new BasicDBObject().append("Yes", "Y")); 
collection2.updateMulti(searchQuery, newDocument);

Over multiple transactions in the loop, I am seeing some memory eat up with the application which is not getting released and after some time my server getting halt and giving "bash fork Cannot allocate memory" error
I have tried ulimit

* soft nofile 65535
  * hard nofile 65535

but nothing happens , also getting below error

> java.lang.OutOfMemoryError: unable to create new native thread
at java.lang.Thread.start0(Native Method)
at java.lang.Thread.start(Thread.java:714)
at java.util.concurrent.ThreadPoolExecutor.addWorker(ThreadPoolExecutor.java:950)
at java.util.concurrent.ThreadPoolExecutor.ensurePrestart(ThreadPoolExecutor.java:1587)
at java.util.concurrent.ScheduledThreadPoolExecutor.delayedExecute(ScheduledThreadPoolExecutor.java:334)
at java.util.concurrent.ScheduledThreadPoolExecutor.scheduleAtFixedRate(ScheduledThreadPoolExecutor.java:573)
at java.util.concurrent.Executors$DelegatedScheduledExecutorService.scheduleAtFixedRate(Executors.java:735)
at com.mongodb.connection.DefaultConnectionPool.createTimer(DefaultConnectionPool.java:316)
at com.mongodb.connection.DefaultConnectionPool.<init>(DefaultConnectionPool.java:75)
at com.mongodb.connection.DefaultClusterableServerFactory.create(DefaultClusterableServerFactory.java:60)
at com.mongodb.connection.BaseCluster.createServer(BaseCluster.java:351)
at com.mongodb.connection.MultiServerCluster.addServer(MultiServerCluster.java:297)
at com.mongodb.connection.MultiServerCluster.addNewHosts(MultiServerCluster.java:360)
at com.mongodb.connection.MultiServerCluster.ensureServers(MultiServerCluster.java:339)
at com.mongodb.connection.MultiServerCluster.handleReplicaSetMemberChanged(MultiServerCluster.java:208)
at com.mongodb.connection.MultiServerCluster.onChange(MultiServerCluster.java:158)
at com.mongodb.connection.MultiServerCluster.access$100(MultiServerCluster.java:44)
at com.mongodb.connection.MultiServerCluster$DefaultServerStateListener.stateChanged(MultiServerCluster.java:121)
at com.mongodb.connection.DefaultServer$DefaultServerStateListener.stateChanged(DefaultServer.java:186)
at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.sendStateChangedEvent(DefaultServerMonitor.java:197)
at com.mongodb.connection.DefaultServerMonitor$ServerMonitorRunnable.run(DefaultServerMonitor.java:164)
at java.lang.Thread.run(Thread.java:745)