CODEWITHSUNDEEP
javamultithreading
user175352
user175352

Reputation:

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

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 how many CPU cycles it costs to create a thread?

Context: In a servlet of a webapplication I want to parallelize the content creation as parts of the content are file based, database based as well as webservices based. But this would mean that for every "http-request-thread" (of my serlvet container) I will have two-to-four additional threads. Note that I will be using the ExecutorService in Java 6.

What should I expect when I use hundreds to thousands of Java threads on a web-server?

Upvotes: 14

Views: 5796

Answers (3)

30thh
30thh

Reputation: 11386

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)

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

Upvotes: 1

Brian Agnew
Brian Agnew

Reputation: 272357

Each thread has its own stack, and consequently there's an immediate memory impact. The default thread stack size is ,IIRC, for Java 6, 512k (different JVMs/version will possibly have different defaults). This figure is adjustable using the -Xss option. Consequently using hundreds of threads will have an impact on the memory the VM consumes (quite possibly before any CPU impact unless those threads are running).

I've seen clients run into problems related to threads/memory, since it's not an obvious link. It's trivial to create 100,000 threads (using executors/pools etc.) and memory problems don't appear to be immediately attributable to this.

If you're servicing many clients, you may want to take a look at the Java NIO API and in particular multiplexing, which allows asynchronous network programming. That will permit you to handle many clients with only one thread, and consequently reduce your requirement for a huge number of threads.

Upvotes: 16

Aaron Digulla
Aaron Digulla

Reputation: 328750

That depends: It depends on the OS, the Java version, and the CPU. The only way to figure this out is to try it and measure the results.

Since you'll be using the ExecutorService, it will be simple to control the number of threads. Don't use too few or requests will stack up. If you use too many, you'll run into performance problems with your file system and the DB long before Java runs out of threads.

Upvotes: 2

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