JDK 14 - Project Loom virtual threads (ex-fibers) test - CAS vs LongAdder performance comparison

fibers.clj

(ns me.core    
  (:import [java.util.concurrent.atomic LongAdder]
           [java.util.concurrent CountDownLatch]))


(defmacro fiber [& body]
  `(.. (Thread/builder)
       (virtual)
       (task (fn [] ~@body))
      ;  (build)
       (start)))

(time
 (let [c (atom 0)
       n (int 1e8)]
   (dotimes [_ n]
     (swap! c inc))
   @c))

;; thread contention - ~10 times slower than 1 thread
(time
 (let [s (atom 0)
       n (int 100)
       doneSignal  (CountDownLatch. n)]
   (dotimes [_ n]
     (fiber
      (dotimes [_ 1e6] (swap! s inc))
      (.countDown doneSignal)))
   (.await doneSignal)
   @s))


(time
 (let [a (LongAdder.)
       n (long 1e8)]
   (dotimes [_ n]
     (.increment a))
   (.sum a)))

;; non-blocking LongAdder - nice! - ~6 times faster on 4 cores than 1 thread
(let [a (LongAdder.)
      n-threads   (int 1000)
      startSignal (CountDownLatch. 1)
      doneSignal  (CountDownLatch. n-threads)]
  (dotimes [_ n-threads]
    (let [t (fiber (do
                     (.await startSignal)
                     (dotimes [_ 100000] (.increment a))
                     (.countDown doneSignal)))]                   
      t))
  (time (do
          (.countDown startSignal)
          (.await doneSignal)
          (.sum a))))