Is Android Context thread safe?

Question

When I use the Android Context within an AsyncTask#doInBackground, is it thread safe? The context is provided via constructor or via getApplicationContext() from a surrounding Activity. This simple questions is asked a lot at stackoverflow and else where but I found not a clear answer?

E.g. in the doInBackground() I use the context in order to Instantiate an DAO class.

 @Override
 protected Void doInBackground(Void... params) {  

   ExampleDao dao = new ExampleDao(context);
   ...

 }

I saw several examples doing that in this way, but I cannot image that this is thread-safe, because the context is now accessed by the main tread (UI Thread) and the worker thread.

Answer 1

You can always access the context from different Thread as long as you are not changing something and you only retrieve resources through the context I don't see a problem with Thread-safety.

The problem is that the context will stay in memory and active as long as the Thread runs. This is a good thing for you because you can rely on having a valid context all the time. The bad thing is that if you pass an Activity as a context all the views and member variables from this activity will also stay in memory and this can lead to a very late garbage collection for a lot of memory, like Waqas suggested.

On thing I would not do from a different Thread is accessing methods from Context subclasses like setTheme() that will affect the currently displayed views.