Thread Pool Callback Mechanism

I am using java.util.concurrent.ExecutorService to create a thread pool. I need a way to inform the user of the progress of the threads in the pool.
Does anyone have any ideas of how to do this?

I am using java.util.concurrent.ExecutorService to
create a thread pool. I need a way to inform the user
of the progress of the threads in the pool.
Does anyone have any ideas of how to do this?Hand the Executor instances of SwingWorker, which implements RunnableFuture. SwingWorker also has a progress() method which can provide progress information.

Similar Messages

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.
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Pattern for Thread Pool?

Hi
i want to build a kind of download manager. The application should be able to handle some concurrent threads, each representing a download in progress.
I thought i might be more efficient to reuse a download thread after the download has ended as to create a new thread each time (like the connection object for db queries). Is this right? If yes, i thought to build a thread pool that serves a limited number of threaded download objects as requested (am I on the right way?).
Now, I have to basic problems: (a) is it right, that, if the run() method of a thread has ended, the whole thread gets destroved? if yes, how should i prevent the thread from being destroyed, so i can reuse it later on? Second (b) how would that pool mechnism look like, means, there must be some kind of vector where i put in and take out the threads.
As you see, these are basic "pool" technique questions. So, I thought, maybe there is a design pattern that would give me the basic mechanism, Does anyone know such a pattern?
Thanks for your help
josh

I thought i might be more efficient to reuse a
download thread after the download has ended as to
create a new thread each time (like the connection
object for db queries). Is this right? If yes, iIt may be right, if creating new threads is wasting enough CPU cycles to justify the complication of a thread pool. Maybe for a high-load server it would be more efficient. You'll have to figure that out for your own specific application.
Another good use for thread pools is to avoid putting time-consuming operations in ActionListeners, etc. Instead you can have them pass the task off to a thread pool, keeping the GUI responsive.
Now, I have to basic problems: (a) is it right, that,
if the run() method of a thread has ended, the whole
thread gets destroved? if yes, how should i prevent
the thread from being destroyed, so i can reuse it
later on? Second (b) how would that pool mechnism look
like, means, there must be some kind of vector where i
put in and take out the threads. (a) You are right. Therefore, the worker threads should not exit their run() methods until interrupted. (b) Worker threads could check a job queue (containing Runnables, perhaps) and if there are none, they should wait() on some object. When another thread adds a new job to the queue, it should call notify() on the same object, thus waking up one of the worker threads to perform the task.
I wrote a thread pool once, just as an exercise. You will run into a number of problems and design issues (such as, what should the worker threads do when interrupted, exit immediately or clear the job queue and then exit?) If you have any more questions, ask in this thead.
Krum

Using AsyncEventHandlers as a RTJ buildin thread pool

Hi David
1. I would like to use AsyncEventHandler mechanism as a thread pool. Would there be a way in future version to access the AsyncEventHandler's RT Thread pool API ?
2. I am using the BoundAsyncEventHandler for long duration task (since the BoundAsyncEventHandler is bound to a specific Thread) - Would there be a way in future version to bound a specific RT Thread to this handler ? - for example a RT Thread that was created by my own Thread pool ?
Thanks

Gabi wrote:
1.We need our code to access the AEH's "thread pool" and check the pool's availability; increase/decrease the pool size dynamically; check pool size for enough free threads to run any given number of tasks and so on...There are no API's for this. How a VM supports AEH execution is an implementation detail, and while a "pool" is the logical form of implementation the details can vary significantly so there's no real way to define an API to control it without defining what form it must take. For example in Java RTS the pool threads are initially at the highest system priority and then drop down to the priority of the AEH they execute. In a different design you might have a pool of threads per priority level (or set of priority levels) so even the notion of increasing/decreasing the pool size is not necessarily straight-forward. In Java RTS the pool will grow as needed to service outstanding AEH activations. You can control the initial number of threads - and there are two pools: one of heap-using and one for non-heap AEH.
2. I was thinking about adding the BAEH class with the next method:
void setBoundThread(RTThread t) throws IllegalArgumentExceptionand also in the Ctor add the RTThread as a parameter.
Inside this method, the thread should be check if started and is so should throw an IllegalArgumentException.Sure, but why do you need to do this? What is different about the RTT that you pass in? The thread executing an AEH acquires the characteristics of the AEH.
An API like this raises some questions such as: when would the thread be started? It also has a problem in that the run() method of the thread has to know how to execute an AEH, which means we'd (the RTSJ expert group) probably have to define a class BoundAEHThread that has a final run() method and you'd then subclass it.
3. Additional question, what do you think about using lock (CountdownLatch) during the AEH's executions ?
I've seen somewhere that AEH should only be used for short live tasks - is it true ? (in the JavaDoc it says there is no problem doing so but I want to be sure)If an AEH blocks for any length of time and additional AEH are activated then the pool management overhead may increase (unless you already sized it appropriately). But otherwise there's no restriction on what the code in an AEH can do. But note that none of the java.util.concurrent synchronization tools support priority-inversion avoidance, so you need to be careful if using them (ie only use them across threads of the same priority and don't expect FIFO access).
David Holmes

Scheduled thread pools and blocking

Hello,
I am using a scheduled thread pool created in the following way:
ScheduledExecutorService scheduler = Executors.newScheduledThreadPool();I want to schedule a task on the scheduler, but this task uses a MulticastSocket and can block on:
byte[] b = new byte[BUFFER_LENGTH];
DatagramPacket dgram = new DatagramPacket(b, b.length);
socket.receive(dgram);Say I schedule this code to run at 500 ms. The first run blocks on the receive method. If the block lasts for more that 500ms, what happens when the scheduler allocates another thread at the next 500ms mark? Can I "lose" a thread from the pool permanently? Can I cause a backup of multiple threads blocking every time the scheduler runs the task?
Thanks!
-pm

Well it used to be a plain old Runnable with the receive() inside the run() method, and the runnable was launched inside a Thread. However, I have an infrastructure that adds tasks to a ScheduledExecutorService so that I can run tasks that require a timing mechanism. I also have an ExecutorService for executing tasks at one time. I want to use these concurrency facilities to get this task to always run, not just once, and I thought scheduling would allow that. Would the ExecutorService's submit() method do that? Would it make more sense to have the run() method loop:
run(){
byte[] b = new byte[BUFFER_LENGTH];
DatagramPacket dgram = new DatagramPacket(b, b.length);
while(true){
socket.receive(dgram);
// do something ...
}and then have ExecutorService simply run execute()?
Thanks!

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 throws reject exceptions even though the queue is not full

Hi. I am using org.springframework.scheduling.concurrent.ThreadPo olTaskExecutor which is based on java
java.util.concurrent.ThreadPoolExecutor
with a enviornment under load.
I see on some cases, that this thread pool throws tasks with reject exception
even though the queue size is 0.
According to the documentation, this thread pool should increase the pool size to core size and then wait untill all queue is full to create new threads.
this is not what happends. for some reason the queue is not filled but exceptions are thrown.
Any ideas why this can happen?

This is the stack trace:
taskExecutorStats-1 2010-04-27 11:01:43,324 ERROR [com.expand.expandview.infrastructure.task_executor] TaskExecutorController: RejectedExecutionException exception in thread: 18790970, failed on thread pool: [email protected]544f07, to run logic: com.expand.expandview.infrastructure.logics.DispatchLogicsProviderLogic
org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@dd9007] did not accept task: com.expand.expandview.infrastructure.task_executor.TaskExecuterController$1@141f728; nested exception is java.util.concurrent.RejectedExecutionException
     at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:305)
     at com.expand.expandview.infrastructure.task_executor.TaskExecuterController.operate(TaskExecuterController.java:68)
     at com.expand.expandview.infrastructure.proxies.DataProxy.callLogic(DataProxy.java:131)
     at com.expand.expandview.infrastructure.proxies.DataProxy.operate(DataProxy.java:109)
     at com.expand.expandview.infrastructure.logics.AbstractLogic.operate(AbstractLogic.java:455)
     at com.expand.expandview.server.app.logics.stats.StatsPersisterSingleChunkLogic.persistSlots(StatsPersisterSingleChunkLogic.java:362)
     at com.expand.expandview.server.app.logics.stats.StatsPersisterSingleChunkLogic.doLogic(StatsPersisterSingleChunkLogic.java:132)
     at com.expand.expandview.infrastructure.logics.AbstractLogic.execute(AbstractLogic.java:98)
     at com.expand.expandview.server.app.logics.ApplicationLogic.execute(ApplicationLogic.java:79)
     at com.expand.expandview.infrastructure.task_executor.TaskExecuterControllerDirect.operate(TaskExecuterControllerDirect.java:33)
     at com.expand.expandview.infrastructure.proxies.LogicProxy.service(LogicProxy.java:62)
     at com.expand.expandview.infrastructure.logics.AbstractLogic.service(AbstractLogic.java:477)
     at com.expand.expandview.server.app.logics.stats.StatsPersisterLogic.persist(StatsPersisterLogic.java:48)
     at com.expand.expandview.server.app.logics.stats.StatsPersisterLogic.doLogic(StatsPersisterLogic.java:19)
     at com.expand.expandview.infrastructure.logics.AbstractLogic.execute(AbstractLogic.java:98)
     at com.expand.expandview.server.app.logics.ApplicationLogic.execute(ApplicationLogic.java:79)
     at com.expand.expandview.infrastructure.task_executor.TaskExecuterController$1.run(TaskExecuterController.java:80)
     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
     at java.lang.Thread.run(Thread.java:619)
Caused by: java.util.concurrent.RejectedExecutionException
     at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:1760)
     at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:767)
     at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:658)
     at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:302)
     ... 19 more

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

The problem in the thread pool implemented by myself

Hello, I need to a thread pool in J2ME CDC 1.0 + FP 1.0, so I implemented a simple one by myself that also meets my own requirement.
Here is the main idea:
The thread pool creates a fixed number of threads in advance. When a task comes, it is put in the waiting list. All threads tries to get the tasks from the waiting list. If no task exists, the threads wait until someone wakes them up.
Here are the requirements from myself:
1. when a task has finished its work in one execution, it is put in the waiting list for the next run.
2. the task can control the delay between when the task owner tries to put it in the waiting list and when the task is actually put in the waiting list. I need this function because sometimes I don't want the tasks to run too often and want to save some CPU usage.
In my program, I creates two thread pools. In one pool, every task don't use the delay, and the thread pool works very well. The other pool has the tasks that use the delay, and sometimes, as I can see from the printed information, there are many tasks in the waiting list but 0 or 1 thread executes tasks. It seems that the waiting threads cannot wake up when new tasks comes.
I suspect the code in addTask(), but cannot find the reason why it fails. Could anyone please help me find out the bug in my code? I put the code of thread pool below
Thank you in advance
Zheng Da
ThreadPool.java
package j2me.concurrent;
import java.util.LinkedList;
import java.util.Timer;
import java.util.TimerTask;
import alvis.general.Util;
public class ThreadPool {
     private int maxQueueSize;
     private boolean running = true;
     private Thread[] threads;
     private LinkedList tasks = new LinkedList();
     private Timer timer = new Timer(true);
     private AtomicInteger usingThreads = new AtomicInteger(0);
     private synchronized boolean isRunning() {
          return running;
     private synchronized void stopRunning() {
          running = false;
     private synchronized PoolTask getTask() {
          while (tasks.isEmpty() && isRunning()) {
               try {
                    this.wait();
               } catch (InterruptedException e) {
                    e.printStackTrace();
          if (tasks.isEmpty())
               return null;
          // Util.log.info(Thread.currentThread().getName() +
          // " gets a task, left tasks: " + tasks.size());
          return (PoolTask) tasks.removeFirst();
     private synchronized void addTaskNoDelay(PoolTask task) {
          tasks.addLast(task);
          notifyAll();
     private synchronized void addTask(final PoolTask task) {
          long delay = task.delay();
          if (delay == 0) {
               addTaskNoDelay(task);
          } else {
               timer.schedule(new TimerTask() {
                    public void run() {
                         addTaskNoDelay(task);
               }, delay);
     private synchronized int numTasks() {
          return tasks.size();
     private class PoolThread extends Thread {
          public void run() {
               Util.poolThreads.inc();
               while (isRunning()) {
                    PoolTask task = getTask();
                    if (task == null) {
                         Util.poolThreads.dec();
                         return;
                    usingThreads.inc();
                    long currentTime = System.currentTimeMillis();
                    task.run();
                    long elapsedTime = System.currentTimeMillis() - currentTime;
                    if (elapsedTime > 100)
                         System.err.println(task.toString() + " takes " + ((double) elapsedTime)/1000 + "s");
                    usingThreads.dec();
                    if (!task.finish()) {
                         addTask(task);
               Util.poolThreads.dec();
     public ThreadPool(int size, int taskQueueSize) {
          maxQueueSize = taskQueueSize;
          threads = new Thread[size];
          for (int i = 0; i < threads.length; i++) {
               threads[i] = new PoolThread();
               threads.start();
     public synchronized boolean executor(PoolTask task) {
          if (!isRunning()) {
               return false;
          Util.log.info("Thread Pool gets " + task + ", there are "
                    + numTasks() + " waiting tasks");
          if (numTasks() >= maxQueueSize) {
               return false;
          addTask(task);
          return true;
     public synchronized void destroy() {
          stopRunning();
          timer.cancel();
          // TODO: I am not sure it can wake up all threads and destroy them.
          this.notifyAll();
     public synchronized void printSnapshot() {
          System.err.println("using threads: " + usingThreads + ", remaining tasks: " + tasks.size());
PoolTask.javapackage j2me.concurrent;
public interface PoolTask extends Runnable {
     * It shows if the task has already finished.
     * If it isn't, the task will be put in the thread pool for the next execution.
     * @return
     boolean finish();
     * It shows the delay in milliseconds that the task is put in the thread pool.
     * @return
     long delay();

are receiving/sends tasks packets time consuming operation in your case or not? if it is not you do not need to use thread pools at all. you can create a queue like in your code through the linked list and dispatch this queue periodically with minimum monitor usage. try this.
import java.util.LinkedList;
public class PacketDispatcher extends Thread {
    LinkedList list = new LinkedList();
    public PacketDispatcher (String name) {
        super(name);
    public void putTask(Task task) {
        synchronized (list) {
            list
                    .add(task);
            list.notify();
    public void run() {
        while (true/* your condition */) {
            Task task = null;
            synchronized (list) {
                while (list.isEmpty())
                    try {
                        list.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                task = (Task)list
                        .poll();
            if (task == null) {
                try {
                    Thread
                            .sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                continue;
            task
                    .run();
            if (!task.isFinished()) {
                putTask(task);
            Thread
                    .yield();
    public static void main(String[] args) {
        // just for test
        try {
            Thread.sleep (10000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        PacketDispatcher dispatcher = new PacketDispatcher("Packet Dispatcher");
        Task task = new Task();
        dispatcher.putTask(task);
        dispatcher.start();
        try {
            Thread.sleep (10000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        Task task2 = new Task();
        dispatcher.putTask(task2);
class Task {
    long result = 0;
    public boolean isFinished () {
        if (getResult() >= 10000000) {
            return true;
        return false;
    public void run() {
        for (int i = 0; i < 1000; i++) {
            result += i;
    public long getResult () {
        return result;
}

Thread Pool Callback Mechanism

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