Thread pool small example needed
Hi friends,
Can you please give a small example program for thread pool to understand?
>
Can you please give a small example program for thread pool to understand?>I don't know (whether you would understand an example - simple or otherwise).
But why don't you help dispel the impression that you are just another lazy student, by making a start on some code, then asking a specific question, when you get stuck?
Similar Messages
-
Freinds,
I need to create a thread pool for one of my application.My knowledge of threads is limited to beginner level. I am just looking out for some pointers that will help me to create thread pool by reading and understanding any of the availble examples.Please send and if possible explain a bit. I really appreciate the fast response from the crowd. Thanks a lot for the help.Hi,
A thread pool is used in situations where you have multiple requests to be serviced and limited resources. A typical example is a server with multiple clients. The server resources are limited and you cant typically create a thread for each client. You would then pick up one of the vacant threads and process the client and put the thread back in the pool. If you dont have any free threads, then you will make the client wait till you have one.
The typical questions you need to ask are, pool size, the kind of waiting scheme (queue, stack, prioritized queue, etc.). Additionally if you need a resizable thread pool you would need to define how the pool should shrink (abort operation and terminate or wait for operation to continue and terminate) and things like this.
If you need a typical implementation of a thread pool, you can go to JavaGuru.com where you have a standard implementation with all relevant details explained.
Prashanth -
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. -
Hi,
I want to write a process that creates a pool of threads that
all process records in the same oracle table.
So, records are inserted by user action. The process will start
threads that fetch a record from that table and transform the
record to a message and the message is sent to another system.
Because only one thread can't handle the amount of messages coming
into the table I need more than one to speed up the handling of
the records.
I would use one main thread that is waiting on an alert so it knows
that a record has been inserted into the table.
What I don't know how to do is how to handle load balancing, etc....
Does anybody have any examples of such a process?
Thanks,
SvenThere are many samples of Java thread pooling on the Internet. Do a google (or search this site) and I'm sure you'll find something that suits.
If not, the O'Reily Java Threads book has a good example.
- K -
Need a procedure with in, out, in out parameters - small example.
Hi Masters,
Need a small example with 3 parameters in a procedure. How to know call by value and call by reference with out and inout parameters.
create or replace procedure sample(x in number, y out number, z in out number) is
begin
pass the x value into y and z as well. and display the 3 values. Code requried..
end;
Thanks a lot in adv.
ARHi,
874273 wrote:
Hi Masters,
Need a small example with 3 parameters in a procedure. How to know call by value and call by reference with out and inout parameters.
create or replace procedure sample(x in number, y out number, z in out number) is
begin
pass the x value into y and z as well. and display the 3 values. Code requried..
end;
Thanks a lot in adv.
AR
I'm not sure I understand the question.
In PL/SQL, the way to pass the value of x to another variable v is:
v := x;
Here, v can be an OUT argument or an IN OUT argument. (It can be any kind of variable except an IN argument or a CONSTANT.)
PL/SQL doesn't really have any way to display values. For debugging, people often use dbms_output, like this:
dbms_output.put_line (y || ' = y inside sample procedure');
Many front end tools (such as SQL*Plus) can display the text after PL/SQL finishes.
By default, all arguments in PL/SQL are passed by value. To call by reference, use the NOCOPY hint, as shown below:
SET SERVEROUTPUT ON;
CREATE OR REPLACE PROCEDURE sample ( x IN NUMBER
, y OUT NUMBER
, z IN OUT NOCOPY NUMBER
IS
BEGIN
y := x;
z := x;
dbms_output.put_line (y || ' = y inside sample procedure');
dbms_output.put_line (z || ' = z');
END sample;
SHOW ERRORS -
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.
~DayI 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.) -
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> -
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 ?
ThanksGabi 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 -
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 advanceUse 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();
} -
Results returned directly from Thread Pool?
Hi there. I wonder is there any example showing an Applicating which use thread pool to process multiple requests and return the results directly back to the client.
Eg:
When calling int doProcess(Runnable process), how can I get some value return from that method?
Most example that I've seen were just showing a void run() method with some print statements.you'll need to use synchronized threads in your run method to ensure that the proper value is returned. look for synchronized thread examples. most examples using one or two threads run in a run() method are gibberish and have no thought put into them.
-
How can I use the same thread pool implementation for different tasks?
Dear java programmers,
I have written a class which submits Callable tasks to a thread pool while illustrating the progress of the overall procedure in a JFrame with a progress bar and text area. I want to use this class for several applications in which the process and consequently the Callable object varies. I simplified my code and looks like this:
threadPoolSize = 4;
String[] chainArray = predock.PrepareDockEnvironment();
int chainArrayLength = chainArray.length;
String score = "null";
ExecutorService executor = Executors.newFixedThreadPool(threadPoolSize);
CompletionService<String> referee = new ExecutorCompletionService<String>(executor);
for (int i = 0; i < threadPoolSize - 1; i++) {
System.out.println("Submiting new thread for chain " + chainArray);
referee.submit(new Parser(chainArray[i]));
for (int chainIndex = threadPoolSize; chainIndex < chainArrayLength; chainIndex++) {
try {
System.out.println("Submiting new thread for chain " + chainArray[chainIndex]);
referee.submit(new Parser(chainArray[i]));
score = referee.poll(10, TimeUnit.MINUTES).get();
System.out.println("The next score is " + score);
executor.shutdown();
int index = chainArrayLength - threadPoolSize;
score = "null";
while (!executor.isTerminated()) {
score = referee.poll(10, TimeUnit.MINUTES).get();
System.out.println("The next score is " + score);
index++;
My question is how can I replace Parser object with something changeable, so that I can set it accordingly whenever I call this method to conduct a different task?
thanks,
TomOK lets's start from the beginning with more details. I have that class called ProgressGUI which opens a small window with 2 buttons ("start" and "stop"), a progress bar and a text area. It also implements a thread pool to conducts the analysis of multiple files.
My main GUI, which is much bigger that the latter, is in a class named GUI. There are 3 types of operations which implement the thread pool, each one encapsulated in a different class (SMAP, Dock, EP). The user can set the necessary parameters and when clicking on a button, opens the ProgressGUI window which depicts the progress of the respective operation at each time step.
The code I posted is taken from ProgressGui.class and at the moment, in order to conduct one of the supported operations, I replace "new Parser(chainArray)" with either "new SMAP(chainArray[i])", "new Dock(chainArray[i])", "new EP(chainArray[i])". It would be redundant to have exactly the same thread pool implementation (shown in my first post) written 3 different times, when the only thing that needs to be changed is "new Parser(chainArray[i])".
What I though at first was defining an abstract method named MainOperation and replace "new Parser(chainArray[i])" with:
new Callable() {
public void call() {
MainOperation();
});For instance when one wants to use SMAP.class, he would initialize MainOperation as:
public abstract String MainOperation(){
return new SMAP(chainArray));
That's the most reasonable explanation I can give, but apparently an abstract method cannot be called anywhere else in the abstract class (ProgressGUI.class in my case).
Firstly it should be Callable not Runnable.Can you explain why? You are just running a method and ignoring any result or exception. However, it makes little difference.ExecutorCompletionService takes Future objects as input, that's why it should be Callable and not Runnable. The returned value is a score (String).
Secondly how can I change that runMyNewMethod() on demand, can I do it by defining it as abstract?How do you want to determine which method to run?The user will click on the appropriate button and the GUI will initialize (perhaps implicitly) the body of the abstract method MainOperation accordingly. Don't worry about that, this is not the point.
Edited by: tevang2 on Dec 28, 2008 7:18 AM -
NIO readiness selection and thread pool
Hi,
I am new to this stuff, but I�m trying to implement readiness selection (using selectors, channels, keys etc). Generally it is not very difficult, I can do it, there are also some examples on the net. The problem is I need it for heavy duty server and I am obligate to use thread pool. I am facing major problems here, especially when fetching keys form the selectedKeys set create tasks for the pool. Can somebody give me some general hints here? Some examples maybe. In every call to Selector.select() the set is filled with new keys, when I give a key to a thread task to be processed, the next selection generates another key for the same channel, because select() is called earlier than thread processing pointed channel finishes and closes the channel.
Generally, basic help needed to implement readiness selection (NIO) with a thread pool.
Thanks for any help.I would do the actual I/O in the same thread as you are selecting in, and use the thread pool to dispatch work arising from the I/O.
If you can't do that you will have to cancel the registration of the key when you pass it off to another thread, or set its interestOps to zero, re-registering or restoring when the thread finishes the action. -
Hello there! I need to implement a solution that will use threads, I write down my problem, to be more precisely on the questions.
The scenario:
An extrator, reads from a flat file, and insert into a table.
Another process runs threads to read this table, perform an ETL and then insert in antoher table. I'm considering that the file read process's time is <<< (much smaller) than the ETL, due the transformations involved.
So my first solution was to use thread pooling (Im reading about, and already have some implementations), since I dont want to have more than a few threads running at same time (let's say 5-6).
Ok my first Ideia was to do something like this:
a main class that will run a thread (the text file extractor), this will be done from the pool of threads, so I have n-1 threads left.
This thread would read the lines and at each 10k read, commit the result, and now its the tricky part, warn its parent process (main class) that it already processed 10k registers. The main class would know that and then start a new thread (the ETL thread, reading from 0-10k) now I have n-2 threads left. The process would go on, since the text thread is faster, It would continue warning the main class, that it had processed 10k registers and main class would continue dispatching new threads, untill it reaches a maximum number (controled by the pool). The pool would be responsible to create its own list of waiting threads to run.
My main problem is to make sure that the text thread can warn the main thread. Can someone point me so directions to it? a tutorial, a hint, anything would helpThread.sleep()
Thread.interrupt()
Well, I'm sorry but I dont think ? I made my self
clear. I need to know how to warn my parent thread not
put the one I'm running in sleep or terminate it.Well. A call to interrupt() does not terminate another thread,
rather, like the name indicates, it interrupts it, but only if
the thread to be interrupted is blocking on a sleep(), join(), or wait() call or is blocking on interruptible I/O (java.nio.channels stuff).
If the thread is not currently blocking, a flag is set.
If there is no need for the parent to sleep() you can just call interrupted() to check the flag at regular intervals. -
I want to use the thread pool to manage the concurrency in Servlet. Who have some examples about it?And would u pls send it to me?thank u.
My mail is [email protected]may i know ur requirement ?
u can make servlet method as synchronise so only one client can access that method at a time, this is the simple way...
let me know ur requirement
i hope that i can help u .....
Any more clarifications needed, please inform me.
[email protected] -
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
AlessioTwo 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.
Maybe you are looking for
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