与 Android 线程、处理程序和处理程序线程的并发性

Question

Ok. So I'm working with the Camera2 API and trying to process all the work in the background so the UI is responsive. I have implemented a HandlerThread and a Handler to put tasks in it like so:

    private void startBackgroundThread(){
         backgroundHandlerThread = new HandlerThread("BackgroundThread");
         backgroundHandlerThread.start();
         backgroundHandler = new Handler(backgroundHandlerThread.getLooper());
    }

Then I post the runnables like so:

    backgroundHandler.post(new ImageSaver(reader.acquireLatestImage()));

The problem is that I use the same handler (backgroundHander) for every runnable I post and I'm getting some serious performance issues. That tells me that I'm not doing concurrency correctly but I'm incapable of finding the correct use of these classes after looking at the docs for several hours. What is the correct approach?

• Creating multiple Handlers for each runnable I post in the HandlerThread?
• Creating multiple HandlerThread for each type of runnable?

Thanks in advance and try not to be harsh on me because I'm pretty noob at this.

Answer 1

Every HandlerThread has a Looper which runs a messsage loop for the thread. Each Looper has a MessageQueue which holds the list of messages being sent to the Looper. Messages and Runnables are sent to the MessageQueue by a Handler . Each one is executed as they come out of the message queue. This process is what is preventing you from "true" concurrency.

An ExecutorService could work here. An ExecutorService allows multiple Runnables to be submitted and executed. From your code snippets above it appeared as though you were using the HandlerThread to put work in the background off the Main or UI Thread. If you are not attempting to relay the work or its result back to the Main Thread, a regular thread and thus an ExecutorService would work as well.

As an Example

...
Executor executor = Executors.newFixedThreadPool(numThreads);
executor.submit(new ImageSaver(reader.acquireLatestImage()));
// submit Runnables as needed
executor.shutdownNow(); // VERY IMPORTANT OR YOU WILL CREATE A MEMORY LEAK!
...

If you need to communicate back to the UI thread, you will need to provide an implementation of the ExecutorService interface like the example in the ExecutorService Usage Examples section of its documentation.