ConcurrentUpsertTest.java

import com.mongodb.BasicDBObject;
import com.mongodb.DBCollection;
import com.mongodb.MongoClient;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ConcurrentUpsertTest {
    public static void main(String[] args) {
        MongoClient client = new MongoClient();

        final DBCollection collection = client.getDB("smoke").getCollection("test");

        collection.drop();

        ExecutorService executorService = Executors.newFixedThreadPool(5);

        // Submit 5 jobs to run concurrently, all upserting a document with the same _id value
        for (int i = 0; i < 5; i++) {
            executorService.submit(() -> {
                while (true) {
                    try {
                        collection.update(new BasicDBObject("_id", 2), new BasicDBObject("$inc", new BasicDBObject("x", 1)), true, false);
                    } catch (Exception e) {
                        System.err.println(e);
                    }
                }
            });
        }
    }

}