Sophisticated threading in android

Question

I'm making an app where I've to perform lot of background operations.

Download data from 30 similar JSON one after the other.
Change priority/order of above mentioned downloads depending upon user response.
Download multiple images parallelly on user request
Stop threads/ check thread status etc.

Which is the best class/API to perform above operation. I've been using AsyncTask but I read somewhere that it has default limitation of 10 background operations and also above functional limitations.

I would also appreciate if you could share peace of code of achieving above tasks.

score 2 · Accepted Answer · edited May 23 '17 at 12:27

You want to use ThreadPools

A ThreadPool is a group of managed Thread, waiting to execute in parallel a set of assigned tasks put on a queue.

Java supply a lot of ways to manage the pool, from simple fixed sized pool to pools that dynamically grow based on the workload to maximise efficiency.

A typical pattern is to use threadpools for all the tasks android does not want you to execute on the UI thread (eg: network operations). However, most of the times your thread will then need to post the result on the UI - and this is prevented from outside the UI thread. This is how your create a thread pool:

ExecutorService threadExecutor = Executors.newFixedThreadPool( 3 );
threadExecutor.execute(new Runnable(){
    public void run(){
        //put here your network code
        //when you get the result, either use
        //view.post(new Runnable...);
        //or
        //AsynchTask
   }
});

Depending on your needs, you can have multiple thread pools for different purposes, but in general, speaking about Android, it is better to keep the overall number of active thread low.

Depending on your hardware, the recommendation is 2 threads per core, but this can vary depending on the proportion of IO-bound (eg network) and CPU-bound (eg graphics) activities.

For prioritising the entries in the queue I would recommend you to create your own ThreadPoolExecutor as in http://www.javamex.com/tutorials/threads/thread_pools_queues.shtml but pass a PriorityQueue instead:

BlockingQueue q = new PriorityQueue<Runnable>();
ThreadPoolExecutor ex = new ThreadPoolExecutor(4, 10, 20, TimeUnit.SECONDS, q);

See also: How to implement PriorityBlockingQueue with ThreadPoolExecutor and custom tasks

Can you share piece of code to re-order priority in a ThreadPool. Is there way a ThreadPool could be binded with AsyncTask ? — Gaurav Arora, Nov 05 '12 at 11:15
If your concern is interacting with the UI, each one of your threads can submit an ASynchThread to the UI - which is by itself a ThreadPool (but you do not have control over it). — thedayofcondor, Nov 05 '12 at 11:23
@GauravTheNewGeek, check out [AsyncTask on Executor and PriorityBlockingQueue](http://stackoverflow.com/questions/12039596/asynctask-on-executor-and-priorityblockingqueue/12045999#12045999). — yorkw, Nov 05 '12 at 22:27
Thanks a lot buddy. Just one more thing how to change priority/order of threads depending upon user response. — Gaurav Arora, Nov 06 '12 at 05:45

score 0 · Answer 2 · answered Nov 05 '12 at 14:03

0

Yes, thread pools are a good solution. But why do it yourself? I manage an open source project on sourceforge.net that can help you get going. I also wrote this article as an introduction: Managing Threads in Android

answered Nov 05 '12 at 14:03

edharned

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Sophisticated threading in android

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