(function() {
    "use strict";

    const conn = MongoRunner.runMongod({nojournal: ""});
    assert.neq(null, conn, "mongod was unable to start up");
    db = conn.getDB("concurrency");
    db.dropDatabase();

    const NRECORDS = 3 * 1024 * 1024;

    print("loading " + NRECORDS + " documents (progress msg every 1024*1024 documents)");
    var bulk = db.conc.initializeUnorderedBulkOp();
    for (var i = 0; i < NRECORDS; i++) {
        bulk.insert({x: i});
    }
    assert.writeOK(bulk.execute());

    print("making an index (this will take a while)");
    db.conc.ensureIndex({x: 1});

    var c1 = db.conc.count({x: {$lt: NRECORDS}});

    const updater = startParallelShell(
        "db = db.getSisterDB('concurrency');\
                                  db.concflag.insert({ inprog: true });\
                                  sleep(20);\
                                  assert.writeOK(db.conc.update({}, \
                                                 { $inc: { x: " +
        NRECORDS +
        "}}, false, true)); \
                                  assert.writeOK(db.concflag.update({}, { inprog: false }));");

    assert.soon(function() {
        var x = db.concflag.findOne();
        return x && x.inprog;
    }, "wait for fork", 30000, 1);

    let querycount = 0;
    let decrements = 0;
    let misses = 0;

    assert.soon(function() {
        const c2 = db.conc.count({x: {$lt: NRECORDS}});
        print(c2);
        querycount++;
        if (c2 < c1)
            decrements++;
        else
            misses++;
        c1 = c2;
        return !db.concflag.findOne().inprog;
    }, "update never finished", 2 * 60 * 60 * 1000, 10);

    print(querycount + " queries, " + decrements + " decrements, " + misses + " misses");

    assert.eq(NRECORDS, db.conc.count(), "AT END 1");

    updater();  // wait()

    MongoRunner.stopMongod(conn);
})();