What is the rough “Cost” of a Thread in CPU cycles and memory?

Question

What is the rough \"cost\" of using threads in java? Are the any rule of thumbs/empirical values, how much memory the creation of one thread costs? Is there a rough estimate

Answer 1

During preparation of a magazine article about Fibers (aka project loom) I run some simple tests (Windows 10, JDK-Loom 15.b3):

AtomicInteger counter = new AtomicInteger(T);
AtomicBoolean go = new AtomicBoolean(false);
for (int i = 0; i < 10000; i++) {
  Thread.newThread(Thread.VIRTUAL, () -> { // <-- remove Thread.VIRTUAL for plain Threads
    while (!go.get()) Thread.sleep(1);
    counter.decrementAndGet();
  }).start();
}

My Windows desktop (i7-8700K) needs about 400000 ms to create all the 10000 threads and additional 200 ms to run the counter down.

Surprisingly I could not confirm the memory consumption of 512k per thread (1Mb according to some other sources). Windows memory monitor shows additional memory consumption of only about 500Mb for all the 10000 threads (50k per thread)

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Project Loom Fibers manage to run the test in 30 respectively 50 ms and show no measurable memory consumption.