"java.lang.OutOfMemoryError : unable to create new native Thread"

We are getting "java.lang.OutOfMemoryError : unable to create new native Thread" on 8GB RAM VM after 32k threads (ps -eLF| grep -c java)

However, "top" and "free -m" shows 50% free memory available. JDk is 64 bit and tried with both HotSpot and JRockit.Server has Linux 2.6.18

We also tried OS stack size (ulimit -s) tweaking and max process(ulimit -u) limits, limit.conf increase but all in vain.

Also we tried almost all possible of heap size combinations, keeping it low, high etc.

The script we use to run application is

/opt/jrockit-jdk1.6/bin/java -Xms512m -Xmx512m -Xss128k -jar JavaNatSimulator.jar /opt/tools/jnatclients/natSimulator.properties

Thanks for the reply.

We have tried editing /etc/security/limits.conf and ulimit but still that same

[root@jboss02 ~]# 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) 72192
max locked memory       (kbytes, -l) 32
max memory size         (kbytes, -m) unlimited
open files                      (-n) 65535
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 10240
cpu time               (seconds, -t) unlimited
max user processes              (-u) 72192
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

Solution 1:

This is not a memory problem even though the exception name highly suggests so, but an operating system resource problem. You are running out of native threads, i.e. how many threads the operating system will allow your JVM to use.

This is an uncommon problem, because you rarely need that many. Do you have a lot of unconditional thread spawning where the threads should but doesn't finish?

You might consider rewriting into using Callable/Runnables under the control of an Executor if at all possible. There are plenty of standard executors with various behavior which your code can easily control.

(There are many reasons why the number of threads is limited, but they vary from operating system to operating system)

Solution 2:

I encountered same issue during the load test, the reason is because of JVM is unable to create a new Java thread further. Below is the JVM source code

if (native_thread->osthread() == NULL) {    
// No one should hold a reference to the 'native_thread'.    
    delete native_thread;   
if (JvmtiExport::should_post_resource_exhausted()) {      
    JvmtiExport::post_resource_exhausted(        
        JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR | 
        JVMTI_RESOURCE_EXHAUSTED_THREADS, 
        "unable to create new native thread");    
    } THROW_MSG(vmSymbols::java_lang_OutOfMemoryError(), "unable to create new native thread");  
} Thread::start(native_thread);`

Root cause : JVM throws this exception when JVMTI_RESOURCE_EXHAUSTED_OOM_ERROR (resources exhausted (means memory exhausted) ) or JVMTI_RESOURCE_EXHAUSTED_THREADS (Threads exhausted).

In my case Jboss is creating too many threads , to serve the request, but all the threads are blocked . Because of this, JVM is exhausted with threads as well with memory (each thread holds memory , which is not released , because each thread is blocked).

Analyzed the java thread dumps observed nearly 61K threads are blocked by one of our method, which is causing this issue . Below is the portion of Thread dump

"SimpleAsyncTaskExecutor-16562" #38070 prio=5 os_prio=0 tid=0x00007f9985440000 nid=0x2ca6 waiting for monitor entry [0x00007f9d58c2d000]
   java.lang.Thread.State: BLOCKED (on object monitor)

Solution 3:

If jvm is started via systemd, there might be a maxTasks per process limit (tasks actually mean threads) in some linux OS.

You can check this by running "service status" and check if there is a maxTasks limit. If there is, you can remove it by editing /etc/systemd/system.conf, adding a config: DefaultTasksMax=infinity