Block thread until callback method has been called by other thread

[James Collett]

Hi All,

Please can you advise best way to block or suspend an application thread, until another thread has called a method in the application's class.

Thank you for your time and help,
Best regards,
James

public class ThreadTester {
  public static void main(String[] args) {
    new ThreadTester().application();
  }
  
  public void application() {
    for (int i=0; i<10; i++) {
      Thread t = new Thread(new Process(this, i));
      t.start();
      /* wait here until serviceSearchCompleted() has been called by Process */
    }
  }
  
  public void serviceSearchCompleted(int number) {
    System.out.println("Completed search " + number);
    /* notify application() method to continue beyond 'waiting point' */
  }
}



class Process implements Runnable {
  private ThreadTester threadTester;
  private int number;
  
  public Process(ThreadTester threadTester, int number) {
    this.threadTester = threadTester;
    this.number = number;
  }
  
  public void run() {
    startSearchServices();
  }
  
  private void startSearchServices() {
    System.out.println("Started search " + number);
    try {
      Thread.sleep(1000);  //...seaching...
    } catch (InterruptedException ie) {}
    threadTester.serviceSearchCompleted(number);
  }
}

[Jeff Verdegan]

If you're asking what I think you're asking, then I usually use a java.util.concurrent.CountdownLatch for that. Something like this, though you'll have to double check method names and args in the docs:

CountdownLatch latch = new CountdownLatch(1); // only needs to be counted down once to release waiting threads

// T1, do stuff, wait till T2 does something, do more stuff
doStuff();
latch.await();
doMoreStuff();

// T2 do stuff, release T2, do more stuff
doStuff();
latch.countDown();
doMoreStuff();

And welcome to the Ranch!

[Jeff Verdegan]

James, please BeForthrightWhenCrossPostingToOtherSites(⇐click) so that people don't waste their time duplicating others' answers. Thanks!


https://forums.oracle.com/forums/thread.jspa?threadID=2388004&tstart=0

[James Collett]

Thank you for your reply. I have managed to RESOLVE this problem using the code below.

public class ThreadTester {
  private Object synchObj = new Object();

  public static void main(String[] args) {
    new ThreadTester().application();
  }
  
  public void application() {
    for (int i=0; i<10; i++) {
      Thread t = new Thread(new Process(this, i));
      t.start();
      synchronized (synchObj) {
        try { synchObj.wait(); } catch (InterruptedException ie) {}
      }
    }
  }
  
  public void serviceSearchCompleted(int number) {
    System.out.println("Completed search " + number);
      synchronized (synchObj) {
        synchObj.notify();
      }
  }
}



class Process implements Runnable {
  private ThreadTester threadTester;
  private int number;
  
  public Process(ThreadTester threadTester, int number) {
    this.threadTester = threadTester;
    this.number = number;
  }
  
  public void run() {
    startSearchServices();
  }
  
  private void startSearchServices() {
    System.out.println("Started search " + number);
    try {
      Thread.sleep(1000);  //...seaching...
    } catch (InterruptedException ie) {}
    threadTester.serviceSearchCompleted(number);
  }
}

[Darryl Burke]

Jeff Verdegan wrote:James, please BeForthrightWhenCrossPostingToOtherSites(⇐click) so that people don't waste their time duplicating others' answers. Thanks!


https://forums.oracle.com/forums/thread.jspa?threadID=2388004&tstart=0

Also at
http://www.java-forums.org/threads-synchronization/59606-block-thread-until-callback-method-has-been-called-other-thread.html
http://www.javaprogrammingforums.com/threads/15650-block-thread-until-callback-method-has-been-called-other-thread.html

edit
http://forums.devshed.com/java-help-9/block-thread-until-callback-method-has-been-called-by-other-904920.html

[Jesus Angeles]

I found such codes useful on 2 occasions:

1) memory: when main thread's default java memory is not enough; main thread has fixed memory while child threads can be set

2) on java gui on desktop or applets: when main thread is doing some processing and another request comes to update gui, the request is not reflected; a child thread can be used to execute the gui request.

[Jeff Verdegan]

Jesus Angeles wrote:I found such codes useful on 2 occasions:

1) memory: when main thread's default java memory is not enough; main thread has fixed memory while child threads can be set

No, it doesn't work that way. The JVM's total memory is set at startup, and it is shared by all threads. Using multiple threads doesn't help with memory usage.

[Jesus Angeles]

Jeff Verdegan wrote:

Jesus Angeles wrote:I found such codes useful on 2 occasions:

1) memory: when main thread's default java memory is not enough; main thread has fixed memory while child threads can be set

No, it doesn't work that way. The JVM's total memory is set at startup, and it is shared by all threads. Using multiple threads doesn't help with memory usage.

I should have specified that I was talking about ThreadStackSize.

[Jeff Verdegan]

Jesus Angeles wrote:

Jeff Verdegan wrote:

Jesus Angeles wrote:I found such codes useful on 2 occasions:

1) memory: when main thread's default java memory is not enough; main thread has fixed memory while child threads can be set

No, it doesn't work that way. The JVM's total memory is set at startup, and it is shared by all threads. Using multiple threads doesn't help with memory usage.

I should have specified that I was talking about ThreadStackSize.

The same thing applies though. You can specify the stack size at startup. I don't know off the top of my head if that's a total size or a per-thread stack size, but it doesn't matter--if you're running out of stack, you can make it bigger. And running out of stack should be a rare occurrence anyway. If you're using multiple threads to alleviate a memory problem, you're doing it wrong.

[Jesus Angeles]

Jeff Verdegan wrote:

Jesus Angeles wrote:

Jeff Verdegan wrote:

Jesus Angeles wrote:I found such codes useful on 2 occasions:

1) memory: when main thread's default java memory is not enough; main thread has fixed memory while child threads can be set

No, it doesn't work that way. The JVM's total memory is set at startup, and it is shared by all threads. Using multiple threads doesn't help with memory usage.

I should have specified that I was talking about ThreadStackSize.

The same thing applies though. You can specify the stack size at startup. I don't know off the top of my head if that's a total size or a per-thread stack size, but it doesn't matter--if you're running out of stack, you can make it bigger. And running out of stack should be a rare occurrence anyway. If you're using multiple threads to alleviate a memory problem, you're doing it wrong.

It is not unusual in my industry (which I prefer not to mention) to require a high stack size.

You are right. The stack size can be set at jvm startup. However, the 'main' thread's stack size is set by each OS. I should have specified, that in the OS I use (Windows XP), the main thread doesnt get the jvm startup setting, because of the reason just mentioned. All child threads however does get the setting.

[Jeff Verdegan]

Jesus Angeles wrote:However, the 'main' thread's stack size is set by each OS. I should have specified, that in the OS I use (Windows XP), the main thread doesnt get the jvm startup setting, because of the reason just mentioned.

Ah, interesting. I wasn't aware of that. (Although I'll be skeptical if it's really the case until I observe it myself or see documentation supporting it.)