anetha anetha - 1 year ago 61
Android Question

Executing a Thread in Asynctask and its complications

I was wondering is it ok to execute a

inside the
method of
. Should I avoid using this kind of structure on my codes? And if yes, why should I avoid it? Would this cause any ineffectiveness in my apps?

Answer Source

In principle, there's no problem with starting a thread in the doInBackground() of an AsyncTask, but sometimes you see this done not because it's the right thing to do, but because of a misunderstanding about how AsyncTask works.

The point is that doInBackground() will automatically get executed on a background (non-GUI) thread, without you needing to create a thread for it yourself. That, in fact, is the whole point of an AsyncTask. So if you have a simple, linear task that you want executed in the background, you do it with an AsyncTask, and you don't need to do any manual thread creation.

Where you might want to start a new thread in an AsyncTask is if you want your background task to use multiple threads to complete. Suppose that you were writing an app to check the online status of various servers, and display something about their status on the screen. You'd use an AsyncTask to do the network access in the background; but if you did it in a naive way, you'd end up with the servers being pinged one by one, which would be rather slow (especially if one was down, and you needed to wait for a timeout). The better option would be to make sure that each server was dealt with on its own background thread. You'd then have a few options, each of which would be defensible:

  1. Have a separate AsyncTask for each server.
  2. Create a thread for each server inside the doInBackground() of your single AsyncTask, and then make sure that doInBackground() doesn't complete until all the individual threads have completed (use Thread.join()).
  3. Use a ThreadPool / some kind of ExecutorService / a fork/join structure inside your single AsyncTask, to manage the threads for you.

I would say that with modern libraries there is rarely a need for manual thread creation. Library functions will manage all of this for you, and take some of the tedium out of it, and make it less error-prone. The third option above is functionally equivalent to the second, but just uses more of the high-level machinery that you've been given, rather than going DIY with your thread creation.

I'm not saying that threads should never be created manually, but whenever you're tempted to create one, it's well worth asking whether there's a high-level option that will do it for you more easily and more safely.

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