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I am trying to continuously start new threads with Java for testing purposes. Here is my code.

import java.util.TimerTask;
import java.util.Timer;

class MakeNewThreads extends TimerTask {
    public static long threadNum=0;
    public void run() {
        Thread thread = new Thread(){
            public void run(){
                try {
                    threadNum++;
                    System.out.println(threadNum);
                    Thread.sleep(10000000);
                } catch(InterruptedException e) { }
            }
        };
        thread.start();
    }
}

public class Main {
    public static void main(String[] args) {
        Timer timer = new Timer();
        timer.schedule(new MakeNewThreads(), 0, 100);
    }
}

However, I meet with the following error before I hit the maximum user process limit.

Exception in thread "Timer-0" java.lang.OutOfMemoryError: unable to create new native thread
    at java.lang.Thread.start0(Native Method)
    at java.lang.Thread.start(Thread.java:714)
    at MakeNewThreads.run(Main.java:16)
    at java.util.TimerThread.mainLoop(Timer.java:555)
    at java.util.TimerThread.run(Timer.java:505)

I have checked the user process limit by ulimit -u. The result is 81920, but I can only create about 11000 threads before I meet with java.lang.OutOfMemoryError. In addition, if I set the user process limit to be lower manually, like 1000, I still cannot even approach the limit (I can create around 400 threads in this case). What could be possible reasons for this? Thanks in advance.

Update 1: I have tried methods mentioned in How to increase maximum number of JVM threads (Linux 64bit)

  1. I tried the sample program in this page. The result is around 11832.

  2. I have tried to run the program with -Xss256K -Xmx1G. The result does not change.

  3. ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 127051
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 81920
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

  4. cat /proc/sys/kernel/threads-max 254103

  5. cat /proc/sys/kernel/pid_max 4194303

  6. cat /proc/sys/vm/max_map_count 262144

Update 2: The problem seems to be solved. When I set the user process limit to 7000. I can create around 7000 threads. I suppose previously it is still the memory problem, but I cannot understand why I can only create up to 11000 threads since 11000*256/1024/1024=2.7G, which is far below the total memory, 32G, of my desktop. I don't think other background threads can take up 30G. Could anyone explain this? Thanks for all the help.

myth
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    This question was raised, try to find an answer - https://stackoverflow.com/a/34452303/5193935 – Andriy Br. Jun 13 '17 at 20:48
  • Have you tried different -Xmx values? What other JVM params have you tried? – Gray Jun 14 '17 at 04:26
  • You cannot create unlimited threads. What are the specs of the machine? 11,000 threads is a _lot_ of threads on a regular development machine. It is not crazy to think you'd run out of memory. – Christopher Schneider Jun 14 '17 at 15:12
  • Try running with `-XX:+HeapDumpOnOutOfMemoryError`. OutOfMemory is very different from hitting the threadlimit error. In your example. I suspect that the new MakeNewThreads class allocation per thread is causing memory pressure as well. – h3adache Jun 14 '17 at 15:19

0 Answers0