Question

I’m doing a download application for android. The downloading part is now successfully implemented and its working.
What I need is to download the file parallel in segments. To be more clear, if the user specify 8 segments, I want to create 8 Threads and do the downloading.
So in what way will I be able to create 8 threads dynamically? Also as I’m doing this for an phone how will I be able to maintain the memory consumption at a minimum level?
I have not worked with threads before, so I hope you can help me with this. Thank you for your time! 🙂

Answer 1

The most efficient way to create a fixed number of threads is to use the ExecutorService:

ExecutorService exec = Executors.newFixedThreadPool(8);

It’s basically a fixed-size thread pool that takes a lot of the management burden from the developer.

Edit: So your flow should be something like this:

First, define your thread task class (each thread will execute the call method of its own task):

class ThreadTask implements Callable<Object> {

    public Object call() {
        // execute download
        ...
        return result;
    }
}

If you want to pass any parameters to the tasks, put some private fields in the class above and pass them through a constructor. Also, you can return any type from call, just change the type in the implements Callable<...> part.

When you want to fire off the threads, create the pool and submit the tasks:

ExecutorService exec = Executors.newFixedThreadPool(8);
List<Future<Object>> results = new ArrayList<Future<Object>>();

// submit tasks
for(int i = 0; i < 8; i++) {
    results.add(exec.submit(new ThreadTask()));
}

...

// stop the pool from accepting new tasks
exec.shutdown();

// wait for results
for(Future<Object> result: results) {
    Object obj = result.get();
}