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

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.