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From "Jeff Kilbride" <>
Subject Re: ** JVM and Processes
Date Fri, 01 Jun 2001 17:34:21 GMT
When Java first came to the Linux platform (via the Blackdown port),
green-threads were the only option. Native threads took a little longer to
implement, but are a much better option for the reasons listed in the
previous message. So, I would recommend avoiding green-threads unless you
have a specific reason for using them.

A lot of people freak out when they see the number of "processes" being
reported by ps or top, without realizing that these are merely threads and
not full-blown processes. If you have a lightly loaded Tomcat, you can tune
down the number of threads being spawned by using the max_threads,
max_spare_threads, and min_spare_threads parameters of the PoolTCPConnector
in your server.xml file. For an example of this, take a look at the tomcat
user's guide:

Do a "find" in your web browser for "max_threads". I use this to limit the
number of ajp12 threads and maximize ajp13 threads -- because I'm using
ajp13 for my servlets and ajp12 only for startup/shutdown of Tomcat.

Conversely, if you have a heavily loaded Tomcat, you should use these
parameters to increase performance.


----- Original Message -----
From: "Michael Jennings" <>
To: <>
Sent: Friday, June 01, 2001 9:32 AM
Subject: Re: ** JVM and Processes

RE: ** JVM and ProcessesMy understanding of green vs. native threads is as
With native threads, an actual system thread is created when a Java thread
is created.
On linux a system thread takes the form of another process, but one that
shares memory
etc. with another process. This is why if you create a program that
allocates 100 megs of memory,
then spins off 10 threads, it looks like 10 processes each taking up 100
megs of memory, when in
fact the amount of memory is 100 megs + 10*overhead for each thread (not
much more than 100 megs).

On WIN32 systems, threads do not show up as separate processes, they are
separate threads of execution
inside the same process (essentially the same as the Linux implementation
with differences too subtle to care about)

Green threads on the other hand use timers, signals, setjmp etc. voodoo to
"simulate" threads within one process.
Essentially taking over the scheduling from the kernel.

I believe the command-line option for green threads is simply "-green" as in
java -green MyThreaddedApp

If you have a multi-cpu system, green threads will only take advantage of
one cpu, whereas native threads
will use all the cpus on your system (that's the theory anyway)

I've heard of problems with blocking I/O with green threads, but have no
first hand knowledge.

Hope this helps.
-Mike Jennings

  ----- Original Message -----
  From: BARRAUD Valérie
  To: ''
  Sent: Friday, June 01, 2001 9:01 AM
  Subject: RE: ** JVM and Processes

    -----Message d'origine-----
    De: []
    Date:   vendredi 1 juin 2001 17:46
    Objet:  RE: ** JVM and Processes


    Thanks for the advice. Could you be a little more specific, though,
    how to use green threads instead of native threads and possibly
    between the two? Thanks.

     - Adam

    At 10:59 AM 6/1/2001 -0400, you wrote:
    >       Don't use ps - these are actually threads.  ps is showing them
    >processes because that is what it does.  If you use green thread (as
    >to the native threads you are using now), the display will go away, but
    >will experience a slowdown (how much depends on your operating system
    >other activity on the system).
    >       Randy
    >> -----Original Message-----
    >> From: []
    >> Sent: Friday, June 01, 2001 10:37 AM
    >> To:
    >> Subject: ** JVM and Processes
    >> Hi,
    >> For a particular web server we are running with Tomcat 3.1,
    >> we are having
    >> an issue with the java servlets that are running. What appears to be
    >> happening is that each time a servlet is called from the web
    >> site, a new
    >> process is created to run the java program. When I view
    >> processes with "ps
    >> ax", I see dozens of instances of:
    >> /usr/java/jdk1.3/bin/i386/native_threads/java
    >> It was briefly stated in Java Servlet Programming by Hunter &
    >> Crawford, (c)
    >> Oreilly that 'most servlet containers execute all servlets in
    >> a single JVM
    >> ... the exception being high-end containers that support
    >> execution across
    >> multiple backend servers...'
    >> We are only using 1 web server with an average weekly load of
    >> a couple of
    >> hundred visitors.
    >> Any ideas as to why we would be seeing so many identical
    >> processes and if
    >> so, how to modify that?
    >> Thanks in advance.
    >>   -Adam

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