java: Patterns for Monitoring worker threads?

and excuse the lack of knowledge on multithreaded apps, but I am new to the field.

Is there a pattern or common used methodology for monitoring the 'job completion' or 'job status' of worker threads from a monitor (a class that acts as a monitor)?

What I have currently done is create a list of workers and create one thread for each worker. After all threads have started i am looping over the wor开发者_StackOverflow中文版ker list and 'checking their status' by making a call to a method.

At that time I couldn't come up with a different solution, but being new to the field, I don't know if this is the way to go, or if there are other solutions or patterns that I should study.

Depending on what you want, there are many ways that you can do this.

If you just want to wait until all the threads finish (i.e. all you care about is having everything finish before moving on), you can use Thread.join():

try {
    for (Thread t: threadsIWaitOn)
        t.join();
} catch (InterruptedException iex) {
     /* ... handle error ... 
}

If you want a more fine-grained control over the thread status and want to be able, at any time, to know what threads are doing, you can use the Thread.getState() function. This returns a Thread.State object that describes whether the thread is running, blocked, new, etc., and the Javadoc specifically says that it's designed for monitoring the state of a thread rather than trying to synchronize on it. This might be want you want to do.

If you want even more information than that - say, how to get a progress indicator for each thread that counts up from 0 to 100 as the thread progresses - then another option might be to create a Map from Threads to AtomicIntegers associating each thread with a counter, then pass the AtomicInteger into the constructor of each thread. That way, each thread can continuously increment the counters, and you can have another thread that continuously polls the progress.

In short, you have a lot of options based on what it is that you're trying to accomplish. Hopefully something in here helps out!

Use a ThreadPool and Executor, then you get a Future<> and you can poll for their completion and some more nice stuff, too. I can appreciate this book for you: Java Concurrency in Practice

Try to use any kind of synchronization. For example, wait on some kind of monitor/semaphore until job is done / whatever you need.