Killing a Thread that runs a C code

Hi,
In my Java application, i use a library written in C++ using JNI. The tasks that are executed by the C library sometimes take a lot of time, so I was considering adding an option for the user to be able to stop it. As these tasks are running in a thread, i was wondering whether there is a way to safely do this?
I have searched the forum, but did not manage to find some post with similar problem. As far as I could see, stopping a thread in general is not safe...
Suggestions guys?
Thanks

shashi_rajak wrote:
you can stop the thread by setting the value of thread to null.---------------> the thread will not be stopped immediately.So setting it to null won't change anything at all. Yes, that's correct, but that isn't what you said previously.
better put a guarded block in the thread code .What's a guarded block?
so that thread will not process the rest of code.Ah, you mean that you need some kind of flag, latch or other way to signal. That's correct, but you never said that (you actually still haven't said that)
>
>
user can again start the thread by starting the thread.-----------------> its mean by creating a new thread object. We aren't mind readers. Calling start of a new thread will of course work, but that isn't what you said.
since you cannot start a already started thread its throws invalid State Exception.Yes, we knew that. That's why we corrected you.
this current forum is not for beginner . Eh. Hmm.. Ok, so I registered in 2000, and have quite many posts, and you came to the conclusion that I'm a beginner?
It has the heading Java Programming " not "New to java". please use your brain.Did you use yours?

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import java.awt.event.*;
import java.awt.image.*;
import java.awt.Graphics.*;
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You can't kill a Thread if it doesn't want to be killed. The deprecated Thread.stop method will atempt to cause an asynchronous ThreadDeath exception in the thread but this is very dangerous as it can leave shared objects - including system library objects - in an unstable and unusable state.
The preferred mechanism is cooperative termination whereby you use the Thread.interrupt method to indicate to the target thread that it should cease what it is doing, when it is safe to do so. The target thread must be responsive to interrupt requests either by directly checking Thread.interrupted, or by using methods that are themselves responsive to interrupts (typically blocking methods that will throw InterruptedException if interrupted). Some blocking methods (mainly IO operations) won't respond to interrupt, nor does the acquisition of a monitor lock, so there are never any guarantees. If the thread can stuck in an "endless loop" then something in that loop needs to check for interrupts.

How to kill a Thread?

Hello,
My question is simple how to kill a thread.
The background is a call to a method in a third party API, crawler4j, that locks the entire program.
The design of crawler4j is "You should stop it when you think it's enough (ctrl+c)" but as I use it only as a step in a larger program I want to stop it programmatically and not by "ctrl+c" as they have designed the API.
This is the locking callcontroller.start(MyCrawler.class, numberOfCrawlers);So I made a thread public class MyCrawlController extends Thread {
public void run(){
controller.start(MyCrawler.class, numberOfCrawlers);
}And in my main method
MyCrawlController mCC = new MyCrawlController();
mCC.start();
Thread.sleep(180000);
//Here I want to kill the mCC and all it's threadsOne problem is that my program never terminates. Probably due too the JVM not realizing that I don't want it to count mCC and it's spawned threads as alive. Any idea on how to solve this. For now I can only exit the program with System.exit(0); and I don't want that. So I need a way to stop the mCC's threads and get the JVM not to count them. Any idea on how to solve this. Even better if they can be taken by the GC.

Farmor wrote:
Thanks for the answer.
I came to think about daemons and solved the problem with mCC.setDaemon(true);Really stupid that one has to do several programs and tie them together only to kill a thread.
As I only do this for other learning purposes and won't use this code or program after this week I will modify crawler4j, open source, and make myself a custom good method that will terminate itself and return to the main method properly.There are some fairly difficult problems with a number of aspects of concurrency if you forcibly stop threads, which is why Thread.stop() and related methods have long been deprecated.
It's a pity that Java can't respond to kill signals (like Ctrl-C) in a tidy way. I think they're all tied up with some of the JVMs internal processes.
In general people wind up using sockets instead of signals.

Kill a thread and remove the element from the vector

Hi All
I have attached each Vector element to a thread which I later want to kill and remove that element from the Vector.
Thread.join(milliseconds) allows this functionality to let the thread die after n milliseconds.
However, I want to delete this element from the Vector now.
Can someone please throw some light on this?
Here the code I have written for this:
try
     System.out.println(counter);
     int xCoord = generator.irand(25,200);     // X-coord of AP
     int yCoord = generator.irand(25,200);     // Y coord of AP
     listMN.addElement(new MobileNode((int)mnId,new Point2D.Double(xCoord,yCoord)));
     listMNcoords.addElement(new Point2D.Double(xCoord,yCoord));
     for(int i=0;i<vnuBS.returnBSList().size();i++)
          if(vnuBS.returnBSListCoords().get(i).contains(xCoord,yCoord)&&(vnuBS.returnBSList().get(i).getChannelCounter()<=3)&&(vnuBS.returnBSList().get(i).getChannelCounter()>0))
               double c = exponential() * 10000;
               long timeToService = (long)c;
               System.out.println("BS "+vnuBS.returnBSList().get(i).id+" is connected to MN ");
               vnuBS.returnBSList().get(i).reduceChannelCounter();
               System.out.println("Channel Counter Value Now: "+vnuBS.returnBSList().get(i).getChannelCounter());
               mobileNodesThread.addElement(new Thread(listMN.elementAt(mobileNodeCounter)));
               mobileNodesThread.elementAt(mobileNodeCounter).setName(mobileNodeCounter+"");
               mobileNodesThread.elementAt(mobileNodeCounter).start();
               mobileNodesThread.elementAt(mobileNodeCounter).join(100);
//                              System.out.println("Died");// thread dies after join(t) milliseconds.
               System.out.println("ListMN getting generated : " + mobileNodesThread.get(mobileNodeCounter));
          else if(vnuBS.returnBSListCoords().get(i).contains(xCoord,yCoord)&&(vnuBS.returnBSList().get(i).getChannelCounter()<=0))
               listMN.remove(this.listMN.lastElement());                         //dropcall
               System.out.println("Removed "+mnId);
               removeCounter++;
               mnId = mnId--;
               mobileNodeCounter--;
          mnId = mnId+1;
     Thanks a lot.

I'm not sure if what you are trying to accomplish is correctly implemented.
The method join does not kill the thread. It will wait for the specified time for the thread to exit. If you want the thread to run for a specified ammount of time, develop the run method of that thread with that in mind. Do not try to kill it from the outside, but let it terminate itself (gracefull termination).
Now for your question regarding the vector (you should probably be using ArrayList nowadays): I would implement the observer pattern for this job. Make the threads post an event on the interface when they are done, let the main thread register itself with the threads and synchronize the method that handles the events. In that method you can remove the object from your list.
I'm not sure if you want to use thread anyhow, could you tell us what it is that you are trying to accomplish?

How many threads are running?

here's the code... i am trying to understand, at each point, how many threads are running:
I understand that one thread belongs to the caller of the start()
& at the same time there is another thread belonging to the instances of each thread (thread1, thread2, thread 3 etc.)
1public class ThreadTester {
2   public static void main( String args[] )
3   {
4      PrintThread thread1, thread2, thread3, thread4;
5
6      thread1 = new PrintThread( "thread1" );
7      thread2 = new PrintThread( "thread2" );
8      thread3 = new PrintThread( "thread3" );
9      thread4 = new PrintThread( "thread4" );
10
11      System.err.println( "\nStarting threads" );
12
13      thread1.start();
14      thread2.start();
15      thread3.start();
16      thread4.start();
17
18      System.err.println( "Threads started\n" );
19   }
}can you tell me if i am counting the number of threads in existance correctly...
LINE#.....CALLER...START...TOTAL THREADS
13..............1.........1.......2
14..............1+1......1+1.....4
15..............2+1......2+1.....6
16..............3+1......3+1.....8
so by the time line 16 executes i have a total of 8 threads,
4 threads belonging to each caller plus
4 threads created by start()
or is it
LINE#.....CALLER...START...TOTAL THREADS
13..............1........1........2
14..............1........1+1.....3
15..............1........2+1.....4
16..............1........3+1.....5
after line 16 executes does the caller thread die, thus leaving only a total of 4 threads?
there is only one thread belonging to the caller at line 13(plus the thread it creates).
at the start of line 14, the previous callers thread is dead & now a new thread is created that belongs to the caller on line 14... etc.

well, i realize at the end there would be 4 threads but im trying to get my head around this explanation in the book:
"A program launches a threads executioin by calling the threads start method, which in turn call the run method. After start launches the thread, start returns to tis caller immediately. The caller then executes concurrently with the lauched thread." there fore if i have 2 concurrent processes, are there 2 threads running????
now having said the above, my question was:
for each line,
how many threads are in existance at
line13
line14
line15
line16
thanks.

Killing a Thread that runs a C code

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