function repro() {

    nthreads = 10

    db.createCollection("c", {writeConcern: {w: "majority"}})

    threads = []
    for (var t=0; t<nthreads; t++) {
        thread = new ScopedThread((t) =>  {
            var ses = db.getMongo().startSession()
            ses.getDatabase("test").c.insert({_id: t, i: 0})
            for (;;) {
                try {
                    ses.startTransaction()
                    ses.getDatabase("test").c.update({_id: t}, {$inc: {i: 1}})
                    //if (t==0) sleep(1000)
                    ses.commitTransaction()
                } catch (e) {
                    print(e)
                }
            }
        }, t)
        threads.push(thread)
        thread.start()
    }
    for (var t = 0; t < nthreads; t++)
        threads[t].join()
}