How Do We Get a Looper from an Executor?

Question

Google's documentation on bound services is promoting using a Messenger in lieu of your own custom binding for IPC. So, I am giving that a try for a particular experiment that I am running.

However, a Messenger needs a Handler. Nowadays, a Handler needs a Looper, and I might want one in this scenario for a background thread anyway (as opposed to Looper.getMainLooper()). The only other Looper that I know how to get is to run() a HandlerThread and get a Looper from it.

The documentation for the deprecated non-Looper forms of the Handler constructor have:

Implicitly choosing a Looper during Handler construction can lead to bugs where operations are silently lost (if the Handler is not expecting new tasks and quits), crashes (if a handler is sometimes created on a thread without a Looper active), or race conditions, where the thread a handler is associated with is not what the author anticipated. Instead, use an Executor or specify the Looper explicitly, using Looper#getMainLooper, View#getHandler, or similar.

(emphasis added)

Is this just strangely-worded documentation, or if there is a recipe for getting a Looper or Handler tied to an Executor that I cannot seem to find?

Answer 1

I think they mean to suggest to use an Executor instead of a Handler. I don't know of any Executor implementation backed by a Looper.

Instead [of a Handler], use an Executor or specify the Looper explicitly, using Looper#getMainLooper, View#getHandler, or similar.

This is useful when you only need to run a Runable. For example the CameraManager.openCamera() method got an overload with the API level 28.

The behavior of this method matches that of openCamera(java.lang.String, StateCallback, android.os.Handler), except that it uses Executor as an argument instead of Handler.

If you require a Messenger, you'll always have to provide a Hanlder backed by a Looper, which was resolved by Looper.getMainLooper(), Looper.myLooper() or from a HandlerThread.

Alternatively you could create a Looper and run loop() on it. But this is basically what a HandlerThread does.