Thread pool of daemon threads?

If I create a Thread, it can be made a daemon thread by invoking setDaemon(true). But what if I create a thread pool via java.util.concurrent.Executors.newFixedThreadPool(NTHREADS)? How can those threads be made daemon threads?
CBy

Thanks Joachim! I didn't know that the newFixedThreadPool method was overloaded.

Similar Messages

Thread pool with AT MOST one thread at a time

Hi,
I want to create a pool that creates at most one thread when it is needed. I want the pool to terminate the thread when it is idle for some time. Executors.newSingleThreadExecutor() creates a thread pool with one thread, but this thread doesn't die if idle...
The code below also doesn't work - no thread is ever created:
new ThreadPoolExecutor(0, 1, 30, TimeUnit.SECONDS,
                          new LinkedBlockingQueue<Runnable>());Thanks in advance

Use Future.get().
package net.jcip.examples;
import java.util.concurrent.*;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
* RenderWithTimeBudget
* Fetching an advertisement with a time budget
* @author Brian Goetz and Tim Peierls
public class RenderWithTimeBudget {
    private static final Ad DEFAULT_AD = new Ad();
    private static final long TIME_BUDGET = 1000;
    private static final ExecutorService exec = Executors.newCachedThreadPool();
    Page renderPageWithAd() throws InterruptedException {
        long endNanos = System.nanoTime() + TIME_BUDGET;
        Future<Ad> f = exec.submit(new FetchAdTask());
        // Render the page while waiting for the ad
        Page page = renderPageBody();
        Ad ad;
        try {
            // Only wait for the remaining time budget
            long timeLeft = endNanos - System.nanoTime();
            ad = f.get(timeLeft, NANOSECONDS);
        } catch (ExecutionException e) {
            ad = DEFAULT_AD;
        } catch (TimeoutException e) {
            ad = DEFAULT_AD;
            f.cancel(true);
        page.setAd(ad);
        return page;
    Page renderPageBody() { return new Page(); }
    static class Ad {
    static class Page {
        public void setAd(Ad ad) { }
    static class FetchAdTask implements Callable<Ad> {
        public Ad call() {
            return new Ad();
}

Thread pool tuning on J2ee NW04s...

Hi,
I have troubles in defining the number of threads in the pool of the server and dispatcher.
First of all, I know that there are several thread pools depending on the node you are:
- Server node: System and Application thread pool.
- Dispatcher: System thread pool.
I know that application pool is dedicated to client requests that come in and system is for the services, libs and core of the nodes.
I'd like to know if I set to a server node a certain number of threads for the System and Application pool, what would be the value of the System thread pool of the dispatcher?
As almost everything is going through the dispatcher before to reach the server node, what would be the number of System threads of the dispatcher if there are two or three server nodes? Should I multiply the number current threads of the dispatcher by the number of server nodes?
If there are a lot of P4 calls (each call needs System 2 threads, one for the request and one for the response) should I deduce the number of thread of the dispatcher using this formula if there is one server node in the worse case:
Dispatcher System Threads = Server App Threads + (Server System Threads x 2)
Thanks in advance,
Serge.

Hi Serge,
One way that you can size the number of threads is by using the monitoring stats in the VA. VA -> cluster -> dispatcher/server -> services -> monitoring -> Runtime (tab) -> Monitor Tree (tab)
then Root -> Kernel
Check the Application Threads Pool and System Threads Pool.
As long as you DON'T experience CPU bottlenecking, then you can increase the number of threads, if:
1) The ActiveThreadsCount is always at the MaximumThreadPoolSize
2) You are noticing the WaitingTasksCount is always high.
If you are experiencing CPU bottlenecking then increasing the number of threads is useless.
Regards
Anthony

What is a daemon thread?

hi all,
can somebody plz tell me what is daemon thread and what is the difference between daemon thread a user thread. thanx in advance..

Daemons are background programs that run all the time
during up-time, ready to do something that may be
required at any point. These are NOT limited to the
JVM, but the concept is mirrored in teh ability to
set a java thread as daemon, as the JVM is just that:
a Virtual Machine that mimics an environment.
Correspondingly OSs have daemon processes (called
d services on windows) e.g. for printing. Calling
Thread.setDaemon() will I believe mark the thread as
to not be destroyed until VM shutdown, and will not
itself stop shutdown of the VM if it is still running.Maybe I got confused by all those nots but if the only threads running are daemon
threads, the VM is allowed to stop; I made that mistake myself several times.
This is what I ripped from the API docs:
The Java Virtual Machine continues to execute threads until either of the following occurs:
- The exit method of class Runtime has been called and the security manager has permitted the exit operation to take place.
- All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method.
It's the "continues to execute until' ... 'all threads that are *not* daemon threads
have died" part. They should have worded that a bit less cryptic ;-)
kind regards,
Jos
ps. First I thought daemon threads run under your bed while drooling sometimes ;-)

Thread callbacks across thread pools

Correct me if I'm wrong, but apparently calls such as PostDeferredCallToThread() don't work between thread pools. If I create a thread pool in a main program (operating in the default thread pool) and make threads, I can't make calls to callbacks in the new thread pool. Thread-safe queues and variables, on the other hand, still seem to work.

See the example in my answer to your other thread.
Proud to use LW/CVI from 3.1 on.
My contributions to the Developer Zone Community
If I have helped you, why not giving me a kudos?

Is garbage collector dameon thread or non dameon thread

hi,
i know daemon thread wil do background process. the garbage collector is daemon thread or non daemon thread.

It is a daemon thread.

BEA-002900 Initializing self-tuning thread pool HANGS

Hi All,
Trying to start a WLS 10.3.5 instance using jrockit and it is hanging on:
Apr 6, 2013 2:08:39 AM CDT> <Info> <WorkManager> <BEA-002900> <Initializing self-tuning thread pool>
end of trace
I took a thread dump and see this:
"[ACTIVE] ExecuteThread: '0' for queue: 'weblogic.kernel.Default (self-tuning)'" id=15 idx=0x3c tid=3810 prio=5 alive, waiting, native_blocked, daemon
-- Waiting for notification on: weblogic/work/ExecuteThread@0xa0c21480[fat lock]
at jrockit/vm/Threads.waitForNotifySignal(JLjava/lang/Object;)Z(Native Method)
at java/lang/Object.wait(J)V(Native Method)
at java/lang/Object.wait(Object.java:485)
at weblogic/work/ExecuteThread.waitForRequest(ExecuteThread.java:162)
^-- Lock released while waiting: weblogic/work/ExecuteThread@0xa0c21480[fat lock]
at weblogic/work/ExecuteThread.run(ExecuteThread.java:183)
at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
-- end of trace
"JFR request timer" id=16 idx=0x40 tid=3811 prio=5 alive, waiting, native_blocked, daemon
-- Waiting for notification on: java/util/TaskQueue@0xa0c20b28[fat lock]
at jrockit/vm/Threads.waitForNotifySignal(JLjava/lang/Object;)Z(Native Method)
at java/lang/Object.wait(J)V(Native Method)
at java/lang/Object.wait(Object.java:485)
at java/util/TimerThread.mainLoop(Timer.java:483)
^-- Lock released while waiting: java/util/TaskQueue@0xa0c20b28[fat lock]
at java/util/TimerThread.run(Timer.java:462)
at jrockit/vm/RNI.c2java(JJJJJ)V(Native Method)
-- end of trace
===== END OF THREAD DUMP ===============
Done:
1). Cleared TMP and CACHE directories and still does not solve the issue.
Any ideas are appreciated.
thanks

Hi,
we had same hang issue. Unfortunately we run behind VM.
It was an issue with securerandom generation.
We solved the issue as described here http://stackoverflow.com/a/2564406/2098832
Also deleted the <server>/tmp directory before.
Hope this helps.
Casey

Aplication server thread pool problem

I'm using sun app server 8.
After some time from starting (and using) the server, it stops responding to clients.
When I change the max number of threads on server the number of clients it can serve before hanging folows the change. So I guess that some threads are not recycled.
But, I can't get full thread dump to see what's happening.
Also I can't get any thread pool monitoring information through asadmin.
(I can see that EJB's are all removed successfuly)
Any suggestions.
Thanks in advance.

First of all, thank you for helping me.
The client wasn't making problems, but server did. (I didn't said that I use the app. server on XP.)
For now I solved the problem by installing the new beta 2004Q4. It works fine now, it also has some thread monitoring in web console...
I was getting this, when I tried to monitor the thread-pool (it is set on HIGH):
asadmin> get -m server.thread-pools.thread-pool.thread-pool-1.*
No matches resulted from the wildcard expression.
CLI137 Command get failed.
If it means anything this is what I was getting when I do ctrl-break. (this thread dump stays the same even after server stops responding...)
Full thread dump Java HotSpot(TM) Client VM (1.4.2_04-b04 mixed mode):
"Thread-6" prio=5 tid=0x02edad08 nid=0xb40 runnable [331f000..331fd8c]
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(FileInputStream.java:177)
at org.apache.commons.launcher.StreamConnector.run(StreamConnector.java:
115)
"Thread-5" prio=5 tid=0x02ebbb98 nid=0x8ac runnable [32df000..32dfd8c]
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(FileInputStream.java:194)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:220)
at java.io.BufferedInputStream.read(BufferedInputStream.java:277)
- locked <0x10089900> (a java.io.BufferedInputStream)
at java.io.FilterInputStream.read(FilterInputStream.java:90)
at org.apache.commons.launcher.StreamConnector.run(StreamConnector.java:
115)
"Signal Dispatcher" daemon prio=10 tid=0x0093dc18 nid=0x930 waiting on condition
[0..0]
"Finalizer" daemon prio=9 tid=0x008a5c20 nid=0xbd0 in Object.wait() [2b5f000..2b
5fd8c]
at java.lang.Object.wait(Native Method)
- waiting on <0x10502a00> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:111)
- locked <0x10502a00> (a java.lang.ref.ReferenceQueue$Lock)
at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:127)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:159)
"Reference Handler" daemon prio=10 tid=0x008a47f0 nid=0xb4 in Object.wait() [2b1
f000..2b1fd8c]
at java.lang.Object.wait(Native Method)
- waiting on <0x10502a68> (a java.lang.ref.Reference$Lock)
at java.lang.Object.wait(Object.java:429)
at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:115)
- locked <0x10502a68> (a java.lang.ref.Reference$Lock)
"main" prio=5 tid=0x000362a0 nid=0xc38 runnable [7f000..7fc3c]
at java.lang.Win32Process.waitFor(Native Method)
at org.apache.commons.launcher.LaunchTask.execute(LaunchTask.java:705)
at org.apache.tools.ant.Task.perform(Task.java:341)
at org.apache.tools.ant.Target.execute(Target.java:309)
at org.apache.tools.ant.Target.performTasks(Target.java:336)
at org.apache.tools.ant.Project.executeTarget(Project.java:1339)
at org.apache.commons.launcher.Launcher.start(Launcher.java:402)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at LauncherBootstrap.main(LauncherBootstrap.java:185)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:324)
at com.sun.enterprise.admin.servermgmt.pe.PEInstancesManager.startInstan
ce(PEInstancesManager.java:115)
at com.sun.enterprise.admin.servermgmt.pe.PEDomainsManager.startDomain(P
EDomainsManager.java:126)
at com.sun.enterprise.cli.commands.StartDomainCommand.runCommand(StartDo
mainCommand.java:59)
at com.sun.enterprise.cli.framework.CLIMain.invokeCommand(CLIMain.java:1
23)
at com.sun.enterprise.cli.framework.CLIMain.main(CLIMain.java:39)
"VM Thread" prio=5 tid=0x0093c698 nid=0x9b4 runnable
"VM Periodic Task Thread" prio=10 tid=0x00940438 nid=0xbd4 waiting on condition
"Suspend Checker Thread" prio=10 tid=0x0093d2b8 nid=0x2c0 runnable

A good design for a single thread pool manager using java.util.concurrent

Hi,
I am developing a client side project which in distinct subparts will execute some tasks in parallel.
So, just to be logorroic, something like that:
program\
            \--flow A\
                       \task A1
                       \task A2
            \--flow B\
                        \task B1
                        \task B2
                        \...I would like both flow A and flow B (and all their launched sub tasks) to be executed by the same thread pool, because I want to set a fixed amount of threads that my program can globally run.
My idea would be something like:
public class ThreadPoolManager {
    private static ExecutorService executor;
    private static final Object classLock = ThreadPoolManager.class;
     * Returns the single instance of the ExecutorService by means of
     * lazy-initialization
     * @return the single instance of ThreadPoolManager
    public static ExecutorService getExecutorService() {
        synchronized (classLock) {
            if (executor != null) {
                return executor;
            } else {
                // TODO: put the dimension of the FixedThreadPool in a property
                executor = Executors.newFixedThreadPool(50);
            return executor;
     * Private constructor: deny creating a new object
    private ThreadPoolManager() {
}The tasks I have to execute will be of type Callable, since I expect some results, so you see an ExecutorService interface above.
The flaws with this design is that I don't prevent the use (for example) of executor.shutdownNow(), which would cause problems.
The alternative solution I have in mind would be something like having ThreadPoolManager to be a Singleton which implements ExecutorService, implementing all the methods with Delegation to an ExecutorService object created when the ThreadPoolManager object is instantiated for the first time and returned to client:
public class ThreadPoolManager implements ExecutorService {
    private static ThreadPoolManager pool;
    private static final Object classLock = ThreadPoolManager.class;
    private ExecutorService executor;
     * Returns the single instance of the ThreadPoolManager by means of
     * lazy-initialization
     * @return the single instance of ThreadPoolManager
    public static ExecutorService getThreadPoolManager() {
        synchronized (classLock) {
            if (pool !=null) {
                return pool;
            } else {
                // create the real thread pool
                // TODO: put the dimension of the FixedThreadPool in a property
                // file
                pool = new ThreadPoolManager();
                pool.executor = Executors.newFixedThreadPool(50);
                // executor = Executors.newCachedThreadPool();
                return pool;
     * Private constructor: deny creating a new object
    private ThreadPoolManager() {
    /* ======================================== */
    /* implement ExecutorService interface methods via delegation to executor
     * (forbidden method calls, like shutdownNow() , will be "ignored")
      // .....I hope to have expressed all the things, and hope to receive an answer that clarifies my doubts or gives me an hint for an alternative solution or an already made solution.
ciao
Alessio

Two things. Firstly, it's better to use     private static final Object classLock = new Object();because that saves you worrying about whether any other code synchronises on it. Secondly, if you do decide to go for the delegation route then java.lang.reflect.Proxy may be a good way forward.

JRun Thread Pool Issue

I'm running CF 9.0.1 on Ubuntu on an "Medium" Amazon EC2 instance. CF has been crashing intermittently (several times per day). At such times, running top gets me this (or something similar):
PID
USER
PR
NI
VIRT
RES
SHR
S
%CPU
%MEM
TIME+COMMAND
15855
wwwrun
20
0
1762m
730m
20m
S
99.3
19.4
13:22.96 coldfusion9
So, it's obviously consuming most of the server resources. The following error has been showing up in my cfserver.log in the leadup to each crash:
java.lang.RuntimeException: Request timed out waiting for an available thread to run. You may want to consider increasing the number of active threads in the thread pool.
If I run /opt/coldfusion9/bin/coldfusion status, I get:
Pg/Sec DB/Sec CP/Sec Reqs Reqs Reqs AvgQ   AvgReq AvgDB Bytes Bytes
Now Hi Now Hi Now Hi Q'ed Run'g TO'ed Time   Time   Time   In/Sec Out/Sec
0   0   0   0   -1 -1 150   25    0     0      -1352560      0      0
In the administrator, under Server Settings > Request Tuning, the setting for Maximum number of simultaneous Template requests is 25. So this makes sense so far. I could just increase the thread pool to cover these sort of load spikes. I could make it 200. (Which I did just now as a test.)
However, there's also this file /opt/coldfusion9/runtime/servers/coldfusion/SERVER-INF/jrun.xml. And some of the settings in there appear to conflict. For example, it reads:
<service class="jrunx.scheduler.SchedulerService" name="SchedulerService">
<attribute name="bindToJNDI">true</attribute>
<attribute name="activeHandlerThreads">25</attribute>
<attribute name="maxHandlerThreads">1000</attribute>
<attribute name="minHandlerThreads">20</attribute>
<attribute name="threadWaitTimeout">180</attribute>
<attribute name="timeout">600</attribute>
</service>
Which a) has fewer active threads (what does this mean?), and b) has a max threads that exceed the simultaneous request limit set in the admin. So, I'm not sure. Are these independent configs that need to be made to match manually? Or is the jrun.xml file supposed to be written by the CF Admin when changes are made there? Hmm. But maybe this is different because presumably the CF Scheduler should only use a subset of all available threads, right...so we'd always have some threads for real live users. We also have this in there:
<service class="jrun.servlet.http.WebService" name="WebService">
<attribute name="port">8500</attribute>
<attribute name="interface">*</attribute>
<attribute name="deactivated">true</attribute>
<attribute name="activeHandlerThreads">200</attribute>
<attribute name="minHandlerThreads">1</attribute>
<attribute name="maxHandlerThreads">1000</attribute>
<attribute name="mapCheck">0</attribute>
<attribute name="threadWaitTimeout">300</attribute>
<attribute name="backlog">500</attribute>
<attribute name="timeout">300</attribute>
</service>
This appears to have changed when I changed the CF Admin setting...maybe...but it's the activeHandlerThreads that matches my new maximum simulataneous requests setting...rather than the maxHandlerThreads, which again exceeds it. Finally, we have this:
<service class="jrun.servlet.jrpp.JRunProxyService" name="ProxyService">
<attribute name="activeHandlerThreads">200</attribute>
<attribute name="minHandlerThreads">1</attribute>
<attribute name="maxHandlerThreads">1000</attribute>
<attribute name="mapCheck">0</attribute>
<attribute name="threadWaitTimeout">300</attribute>
<attribute name="backlog">500</attribute>
<attribute name="deactivated">false</attribute>
<attribute name="interface">*</attribute>
<attribute name="port">51800</attribute>
<attribute name="timeout">300</attribute>
<attribute name="cacheRealPath">true</attribute>
</service>
So, I'm not certain which (if any) of these I should change and what exactly the relationship is between maximum requests and maximum threads. Also, since several of these list the maxHandlerThreads as 1000, I'm wondering if I should just set the maximum simultaneous requests to 1000. There must be some upper limit that depends on available server resources...but I'm not sure what it is and I don't really want to play around with it since it's a production environment.
I'm not sure if it pertains to this issue at all, but when I run a ps aux | grep coldfusion I get the following:
wwwrun   15853 0.0 0.0   8704   760 pts/1
S
20:22   0:00 /opt/coldfusion9/runtime/bin/coldfusion9 -jar jrun.jar -autorestart -start coldfusion
wwwrun   15855 5.4 18.2 1678552 701932 pts/1
Sl
20:22   1:38 /opt/coldfusion9/runtime/bin/coldfusion9 -jar jrun.jar -start coldfusion
There are always these two and never more than these two processes. So there does not appear to be a one-to-one relationship between processes and threads. I recall from an MX 6.1 install I maintained for many years that additional CF processes were visible in the process list. It seemed to me at the time like I had a process for each thread...so either I was wrong or something is quite different in version 9 since it's reporting 25 running requests and only showing these two processes. If a single process can have multiple threads in the background, then I'm given to wonder why I have two processes instead of one...just curious.
So, anyway, I've been experimenting while composing this post. As noted above I adjusted the maximum simulataneous requests up to 200. I was hoping this would solve my problem, but CF just crashed again (rather it slogged down and requests started timing out...so effectively "crashed"). This time, top looked similar (still consuming more than 99% of the CPU), but CF status looked different:
Pg/Sec DB/Sec CP/Sec Reqs Reqs Reqs AvgQ   AvgReq AvgDB Bytes Bytes
Now Hi Now Hi Now Hi Q'ed Run'g TO'ed Time   Time   Time   In/Sec Out/Sec
0   0   0   0   -1 -1 0     150   0     0      0      0      0      0
Obviously, since I'd increased the maximum simultaneous requests, it was allowing more requests to run simultaneously...but it was still maxing out the server resources.
Further experiments (after restarting CF) showed me that the server became unusably slogged after about 30-35 "Reqs Run'g", with all additional requests headed for an inevitible timeout:
Pg/Sec DB/Sec CP/Sec Reqs Reqs Reqs AvgQ   AvgReq AvgDB Bytes Bytes
Now Hi Now Hi Now Hi Q'ed Run'g TO'ed Time   Time   Time   In/Sec Out/Sec
0   0   0   0   -1 -1 0     33    0     0      -492   0      0      0
So, it's clear that increasing the maximum simultaneous requests has not helped. I guess what it comes down to is this: What is it having such a hard time with? Where are these spikes coming from? Bursts of traffic? On what pages? What requests are running at any given time? I guess I simply need more information to continue troubleshooting. If there are long-running requests, or other issues, I'm not seeing it in the logs (although I do have that option checked in the admin). I need to know which requests exactly are those responsible for these spikes. Any help would be much appreciated. Thanks.
~Day

I really appreciate your help. However, I haven't been able to find the JRun Thread settings you describe above.
Under Request Tuning, I see:
Server Settings > Request Tuning
Request Limits
Maximum number of simultaneous Template requests
Restricts the number of simultaneously processed requests. Use this setting to increase overall system performance for heavy load applications. Requests beyond the specified limit are queued. On Standard Edition, you must restart ColdFusion to enable this setting.
Maximum number of simultaneous Flash Remoting requests
The number of Flash Remoting requests that can be processed concurrently.
Maximum number of simultaneous Web Service requests
The number of Web Service requests that can be processed concurrently.
Maximum number of simultaneous CFC function requests
The number of ColdFusion Component methods that can be processed concurrently via HTTP. This does not affect invocation of CFC methods from within CFML, only methods requested via an HTTP request.
Tag Limit Settings
Maximum number of simultaneous Report threads
The maximum number of ColdFusion reports that can be processed concurrently.
Maximum number of threads available for CFTHREAD
The maximum number of threads created by CFTHREAD that will be run concurrently. Threads created by CFTHREAD in excess of this are queued. On Standard Edition, the maximum limit is 10.
And under Java and JVM, I see:
Server Settings > Java and JVM
    Java and JVM settings control the way ColdFusion starts the Java Virtual Machine when it starts. You can control settings like what classpaths are used and how memory is allocated as well as add custom command line arguments. Changing these settings requires restarting ColdFusion. If you enter an incorrect setting, ColdFusion may not restart properly.
   Backups of the jvm.config file are created when you hit the submit button. You can use this backup to restore from a critical change.
   Java Virtual Machine Path
Specifies the location of the Java Virtual Machine.
   Minimum JVM Heap Size (MB)         Maximum JVM Heap Size (MB)
   The Memory Size settings determine the amount of memory that the JVM can use for programs and data.
   ColdFusion Class Path
Specifies any additional class paths for the JVM, with multiple directories separated by commas.
   JVM Arguments
-server -Dsun.io.useCanonCaches=false -XX:MaxPermSize=192m -XX:+UseParallelGC -Xbatch -Dcoldfusion.rootDir={application.home}/../ -Dcoldfusion.libPath={application.home}/../lib
Specifies any specific JVM initialization options, separated by spaces.
I did go take a look at FusionReactor and found it's not free (which would be fine, of course, if it would actually help). It looks like there's a fully functional demo, which is cool...but I've haven't been able to get it to install yet, so we'll see.
Thanks again!
~Day
(By the way, I've cross-posted this inquiry on StackOverflow. So if you're able to help me arrive at a solution you might want to answer there as well.)

Custom thread pool for Java 8 parallel stream

It seems that it is not possible to specify thread pool for Java 8 parallel stream. If that's so, the whole functionality is useless in most of the situations. The only situation I can safely use it is a small single threaded application written by one person.
In all other cases, if I can not specify the thread pool, I have to share the default pool with other parts of the application. If someone submits a task that takes a lot of time, my tasks will get stuck. Is that correct or am I overlooking something?
Imagine that someone submits slow networking operation to the fork-join pool. It's not a good idea, but it's so tempting that it will be happening. In such case, all CPU intensive tasks executed on parallel streams will wait for the networking task to finish. There is nothing you can do to defend your part of the application against such situations. Is that so?

You are absolutely correct. That isn't the only problem with using the F/J framework as the parallel engine for bulk operations. Have a look http://coopsoft.com/ar/Calamity2Article.html

Thread pool rejecting threads when I don't think it should, ideas?

Hi,
I have a server application in which I only want a specific number of simultaneous requests. If the server gets more then this number it is suppose to close the connection (sends an HTTP 503 error to the client). To do this I used a fix thread pool. When I start the server and submit the max number of requests I get the expected behavior. However if I resubmit the request (within a small period of time, e.g. 1-15 seconds after the first one) I get very odd behavior in that some of the requests are rejected. For example if I set the max to 100 the first set of requests will work fine (100 requests, 100 responses). I then submit again and a small number will be rejected (I've seen it range from 1 to 15 rejected)....
I made a small app which kind of duplicates this behavior (see below). Basically when I see is that the first time submitting requests works fine but the second time I get a rejected one. As best as I can tell none should be rejected....
Here is the code, I welcome your thoughts or if you see something I am doing wrong here...
<pre>
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;
public class ThreadPoolTest {
     static AtomicInteger count = new AtomicInteger();
     public static class threaded implements Runnable {
          @Override
          public void run() {
               System.out.println("In thread: " + Thread.currentThread().getId());
               try {
                    Thread.sleep(500);
               } catch (InterruptedException e) {
                    System.out.println("Thread: " + Thread.currentThread().getId()
                              + " interuptted");
               System.out.println("Exiting run: " + Thread.currentThread().getId());
     private static int maxThreads = 3;
     private ThreadPoolExecutor pool;
     public ThreadPoolTest() {
          super();
          pool = new java.util.concurrent.ThreadPoolExecutor(
                    1, maxThreads - 1, 60L, TimeUnit.SECONDS,
                    new ArrayBlockingQueue<Runnable>(1));
     public static void main(String[] args) throws InterruptedException {
          ThreadPoolTest object = new ThreadPoolTest();
          object.doThreads();
          Thread.sleep(3000);
          object.doThreads();
          object.pool.shutdown();
          try {
               object.pool.awaitTermination(60, TimeUnit.SECONDS);
          } catch (InterruptedException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
     private void doThreads() {
          int submitted = 0, rejected = 0;
          int counter = count.getAndIncrement();
          for (int x = 0; x < maxThreads ; x++) {
               try {
                    System.out.println("Run #: " + counter + " submitting " + x);
                    pool.execute(new threaded());
                    submitted++;
               catch (RejectedExecutionException re) {
                    System.err.println("\tRun #: " + counter + ", submission " + x
                              + " was rejected");
                    System.err.println("\tQueue active: " + pool.getActiveCount());
                    System.err.println("\tQueue size: " + pool.getPoolSize());
                    rejected++;
          System.out.println("\n\n\tRun #: " + counter);
          System.out.println("\tSubmitted: " + (submitted + rejected));
          System.out.println("\tAccepted: " + submitted);
          System.out.println("\tRejected: " + rejected + "\n\n");
</pre>

First thank you for taking the time to reply, I do appreciate it.
jtahlborn - The code provided here is a contrived example trying to emulate the bigger app as best as I could. The actual program doesn't have any sleeps, the sleep in the secondary thread is to simulate the program doing some work & replying to a request. The sleep in the primary thread is to simulate a small delay between 'requests' to the pool. I can make this 1 second and up to (at least) 5 seconds with the same results. Additionally I can take out the sleep in the secondary thread and still see the a rejection.
EJP - Yes I am aware of the TCP/IP queue, however; I don't see that as relevant to my question. The idea is not to prevent the connection but to respond to the client saying we can't process the request (send an "HTTP 503" error). So basically if we have, say, 100 threads running then the 101st, connection will get a 503 error and the connection will be closed.
Also my test platform - Windows 7 64bit running Java 1.6.0_24-b07 (32bit) on an Intel core i7.
It occurred to me that I did not show the output of the test program. As the output shows below, the first set of requests are all processed properly. The second set of requests is not. The pool should have 2 threads and 1 slot in the queue, so by the time the second "request" is made at least 2 of the requests from the first call should be done processing, so I could possibly understand run 1, submit #2 failing but not submit 1.
<pre>
Run #: 0 submitting 0
Run #: 0 submitting 1
Run #: 0 submitting 2
In thread: 8
In thread: 9
Exiting run: 8
Exiting run: 9
     Run #: 0
     Submitted: 3
     Accepted: 3
     Rejected: 0
In thread: 8
Exiting run: 8
Run #: 1 submitting 0
In thread: 9
Run #: 1 submitting 1
     Run #: 1, submission 1 was rejected
     Queue active: 1
     Queue size: 2
Run #: 1 submitting 2
     Run #: 1
     Submitted: 3
     Accepted: 2
     Rejected: 1
In thread: 8
Exiting run: 9
Exiting run: 8
</pre>

Thread Pool , Executors ...

Sorry if i make a stupid post now, but i'm looking for a implementation of a Thread Pool using the latest 1.5 java.util.concurrent classes and i can't find anything serious. Any implementation or link to a tutorial should be vary helpful.
Thnx

but i'm looking
for a implementation of a Thread Pool using
the latest 1.5 java.util.concurrent classes and i
can't find anything serious. Any implementation or
link to a tutorial should be vary helpful.
Thnxhere is an Example :
import java.util.concurrent.*;
public class UtilConcurrentTest {
public static void main(String[] args) throws InterruptedException {
int numThreads = 4;
int numTasks = 20;
ExecutorService service = Executors.newFixedThreadPool(numThreads);
// do some tasks:
for (int i = 0; i < numTasks; i++) {
service.execute(new Task(i));
service.shutdown();
log("called shutdown()");
boolean isTerminated = service.awaitTermination(60, TimeUnit.SECONDS);
log("service terminated: " + isTerminated);
public static void log(String msg) {
System.out.println(System.currentTimeMillis() + "\t" + msg);
private static class Task implements Runnable {
private final int id;
public Task(int id) {
this.id = id;
public void run() {
log("begin:\t" + this);
try { Thread.sleep(1000); } catch (InterruptedException e) {}
log("end\t" + this);
public String toString() {
return "Task " + id + " in thread " + Thread.currentThread().getName();
}

Thread pool executor problem

When using a thread pool executor (java.util.concurrent.ThreadPoolExecutor) to limit the number of threads executing at a time, the number of threads running still exceeds the limit number.
This is the code:
private ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 3, 20, TimeUnit.SECONDS, new LinkedBlockingQueue());
The number of tasks in my program are 4, so i always have 4 threads running, although i limited it to 3.
Can anyone help me with this problem? Or can u propose another solution to limit the number of running threads? By the way, i also tried using a newFixedThreadPool() and got the same problem.
Thx.

The number of tasks in my program are 4, so i always
have 4 threads running, although i limited it to 3.How do you know that there are 4 threads running? If you're generating a JVM thread dump, you're going to see threads that are used internally by the JVM.
Here's a simple program that creates a fixed-size threadpool and runs jobs. It limits the number of concurrent threads to 3. Compare it to what you're doing, I'm sure that you'll find something different. Also, verify that you're not creating threads somewhere else in your program; all of the ThreadPoolExecutor threads will have names of the form "pool-X-thread-Y"
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
public class ThreadPoolTest {
    public static void main(String[] args) {
        ExecutorService pool = Executors.newFixedThreadPool(3);
        for (int ii = 0 ; ii < 10 ; ii++) {
            pool.execute(new MyRunnable());
        pool.shutdown();
    private static class MyRunnable implements Runnable {
        public void run() {
            log("running");
            try {
                Thread.sleep(1000L);
            catch (InterruptedException e) {
                log("interrupted");
        private void log(String msg) {
            System.err.println(
                    msg + " on " + Thread.currentThread().getName()
                    + " at " + System.currentTimeMillis());
}

Thread pool in servlet container

Hello all,
I'm working on this webapp that has some bad response times and I've identified an area were we could shave off a considerable amount of time. The app is invoking a component that causes data to be catched for subsequently targeted apps in the environemnt. Our app does not need to wait for a response so I'd like to make this an asyncronous call. So, how best to implement this?...I considered JMS, but started working on a solution using the Java 1.4 backport of JSR 166 (java.util.concurrent).
I've been testing the use of a ThreadPoolExecutor, using an ArrayBlockingQueue. The work that each Runnable will perform involves a lot of waiting (the component we call invokes a web service, among a couple other distributed calls). So I figure the pool will be much larger than the queue. Our container has 35 execute threads, so I've been testing with a thread pool size of 25, and a queue of 10.
Any thoughts on this approach? I understand that some of this work could be simplified by JMS, but if I don't need to be tied to the container, I'd prefer not to. The code if much easier to unit test, and plays nicely with our continious build integration (which runs our junit test for us and notifies on errors).
Any thoughts are greatly appreciated...Thanks!!

Well, if it works, that's by far the best way to go - but note that creating threads in a servlet container means those threads are outside of the container's control. Many containers will refuse to give the new threads access to the JNDI context, even, and some may prevent you from creating threads at all.

Thread pool of daemon threads?

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