java.lang.OutOfMemoryError: unable to create new native thread

Question

i saw comment like this

one place i have seen this problem is if you keep creating threads, and instead of calling start(), call run() directly on the thread object. This will result in the thread object not getting dereferenced... So after sometime the message unable to create new native thread comes up

on the Sun Java Forums

In my application, initialy we plan to use thread, but later, we decided no need anymore, so we just call run() instead of start(). Do we need to do manual GC for new threadClass(..) ?

my tomcat startup setting

-Xms1024m -Xmx1024m -XX:MaxPermSize=450m 

Answer 1

When you call run() method no new thread should be created. And your objects will be collected by Garbage collector when they are not referenced.

Your other part of code may be creating lot of Threads.

Try using ThreadPoolExecutor (thread pooling) in your code to limit threads in your application, And tune your threadpool size accordingly for better performance.

You can also check following to debug your issue: (referenced from link) There are a few things to do if you encounter this exception.

• Use the lsof -p PID command (Unix platforms) to see how many threads are active for this process.
• Determine if there is a maximum number of threads per process defined by the operating system. If the limit is too low for the application, try raising the per-process thread limit.
• Examine the application code to determine if there is code that is creating threads or connections (such as LDAP connections) and not destroying them. You could dump the Java threads to see if there are an excessive number has been created.
• If you find that too many connections are opened by the application, make sure that any thread that the application creates is destroyed. An enterprise application (.ear) or Web application (.war) runs under a long-running JVM. Just because the application is finished does not mean that the JVM process ends. It is imperative that an application free any resources that it allocates. Another solution would be for the application to use a thread pool to manage the threads needed.

Answer 2

Why do you create a Thread in the first place?

Your code should implement the Runnable interface instead.

Then, when you decide that you want to run it in a thread, simple instantiate a Thread with the Runnable as the argument and call start() on the Thread object.

If, instead, you just want to run it in your current thread, simply call run() on your Runnable object.

This has several advantages:

• you don't involve any Thread objects as long as you don't care about separate threads
• your code is wrapped in a Runnable which fits closer conceptually: you're not writing some special kind of Thread, do you? You simply write some code that can be executed/run.
• you can easily switch to using an Executor which further abstract away the decision

And last but not least you avoid any potential confusion on whether or not a native thread resource is created.