OS X Java maximum threads per process

Question

Running this code

        for (int i = 0; i < 4000; i++) {
            new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        Thread.sleep(60000);
                    } catch (InterruptedException e) {
                    }
                }
            }).start();
            System.out.println(i);
        }

results in

Exception in thread "main" java.lang.OutOfMemoryError: unable to create new native thread
    at java.lang.Thread.start0(Native Method)
    at java.lang.Thread.start(Thread.java:658)
    at com.codeoverdrive.burnbearburn.Main.main(Main.java:10)

after 2024 running threads. Playing with JVM heap and stack sizes does not help.

sysctl kern.num_threads

returns

kern.num_threads: 10240

OS X Mountain Lion 10.8.4, Macbook Air with 4GB RAM

Any suggestions?

Answer 1

The most probable cause is that the user you are running with has a limit on the number of threads it can create.

Try and increase this limit. The current limit can be shown by the ulimit -u command. Note that as a regular user you probably won't be able to increase it, you'll have to modify the environment as root.

And yes, OutOfMemoryError is misleading in this case.