Re: Unlimited threads being created

Eric Sosman <>
Tue, 18 Mar 2008 17:21:11 -0400
Hugo wrote:


I have a three servlet classes in a Tomcat where I use the
ExetorServices to create a thread pool. The thread pool is used to
execute tasks so that the main thread does not slow down.

Problem: Tomcat crashes with an out of memory error:
"<snip>java.lang.OutOfMemoryError: unable to create new native thread)

From looking at the logs, each time a servlet was called a new thread
was created. I am guessing that the Tomcat ran until the process ran
out of threads. I thought that the maximum number of threads that can
be created by the thread pool will be listed by the
newFixedThreadPool() method.

Sample of the code is below, can anyone help me out on where I have
gone wrong?

Public Class Foo extends HTTPServlet

  ExecutorService pool = Executors.newFixedThreadPool(1000);

     A thousand threads? That's a LOT of threads! I'm not
surprised you ran out of memory.

     Also, how many hardware execution units ("CPU's," "cores,"
"strands") does your system have, and how does that number
compare to a thousand? Unless your threads are spending a
whole lot of time doing nothing (e.g., waiting for something
slow like I/O), they'll thrash the scheduler to death. Ever
seen a thousand people scramble for the same elevator?

     Reduce the thread count to something sane and try again.


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