java - listener when new created thread attached to my custom ThreadGroup

Question

I know a bit about multi-thread programming in java

as I know any newly created thread is attached to the current ThreadGroup by default. and if you create a new ThreadGroup, its attached as a child to current ThreadGroup.

I've written a modular program as below:

• each module is extended the class Module
• each module has its own thread pool with size of 5
• each module has its own instance of a CustomThreadGroup
• each module started in its own thread pool
• executed by invoking modules' onCreate() method in a runnable posted to its thread pool

imagine we have something like below to start each module:

for(final Module mod : modules){
    mod.executor.execute(new Runnable() {

        @Override
        public void run() { 
            mod.onCreate();
        }
    });
}

executor is a thread pool with a custom ThreadFactory which add module's instance of CustomThreadGroup to newly created Thread by thread pool.

now I can make sure any module is launched in its own thread pool and any method invoked in onCreate is executed in the same thread. if module wants to run a long running task, it should post a new runnable to its executor or run a new Thread.

so, I can get any module's Threads recursively by invoking module's CustomThreadGroup.enumerate(n, true)

for this scenario I wrote below code:

while(true){
    for(Module mod : modules){
        CustomThreadGroup tg = mod.getThreadGroup();
        Thread threads[] = tg.getThreads(); // invoke enumerate internally
        // my tasks for classifying threads
    }
    Thread.sleep(5 * 1000); // sleep for 5 secs
    // then recalculate threads count
}

it works well in a seperate thread to calculated threads count which will be newly created in onCreate() method of module.

so my question is:

how can I be notified about newly created threads attached to ThreadGroup without executing an infinite loop?

sorry for my bad English.

Answer 1

You can use a CountDownLatch

final CountDownLatch cdl = new CountDownLatch(modules.size());

for (final Module mod : modules) {
    mod.executor.execute(new Runnable() {
        @Override
        public void run() {
            mod.onCreate(cdl);
            // TODO in mod.onCreate
            // cdl.countDown();
        }
    });
}

// Waiting all module
cdl.await();
// All module are started