Close CameraDevice in a seperate thread

问题

I am using Android camera2 to create a custom camera. The cameraDevice.close() method is slow and it makes UI freeze for 1 sec. I put it in another thread and it seems to work just fine. I want to know if this will cause some serious problem and whether there is another way to achieve this. Here is my closeCamera method:

private void closeCamera() {
    boolean release = false;
    try {
        mCameraOpenCloseLock.acquire();
        release = true;
    } catch (InterruptedException e) {
        release = false;
    }
    try {
        preparing = true;
        if (mCaptureSession != null) {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M && mCaptureSession.isReprocessable()
                    || validCameraSession) {
                mCaptureSession.close();
            }
            mCaptureSession = null;
            validCameraSession = false;
        }
    } catch (IllegalStateException e) {
        mCaptureSession = null;
    } catch (Exception e) {
        mCaptureSession = null;
    }
    try {
        new Thread(new Runnable() {
            @Override
            public void run() {
                if (mCameraDevice != null) {
                    if (openCamera) {
                        mCameraDevice.close();
                        mCameraDevice = null;
                    }
                }
            }
        }).start();

    } catch (IllegalStateException e) {
        Log.e(TAG, "closeCamera: mCaptureSession - ", e);
    } catch (Exception e) {
        Log.e(TAG, "closeCamera: mCaptureSession - ", e);
    }

    if (release) {
        if (mCameraOpenCloseLock != null) {
            int lock = mCameraOpenCloseLock.availablePermits();
            if (lock > 1) mCameraOpenCloseLock.release(lock - 1);
            else if (lock == 0) mCameraOpenCloseLock.release();
        }
    }
}

I think it may cause crash when mCameraDevice has not been closed but user open camera again. But it is rare case, and I am thinking of putting another check before open camera again. I don't want my UI to freeze 1 sec for it to close, is there any other way I can achieve that except putting it in seperate thread?

回答1:

As far as I know, such freeze with cameraDevice.close() happens on some unfortunate devices, and sometimes is cured by performing a normal system upgrade.

But this is a little consolation if this happens to you, on your device. Actually, you are kind of lucky that you can prepare a fix for that. The end-users of your app will benefit from your misfortune.

Your code looks OK, if it delivers desired improvements for you. As I explained, it may be hard to reproduce this problem on another device.

I would rather put all closeCamera() logic on the same background thread. If you provided a Handler to openCamera(), as in the official example,

manager.openCamera(mCameraId, mStateCallback, mBackgroundHandler);

then I would suggest posting all closeCamera() sequence to this mBackgroundHandler.

回答2:

As Alex Cohn mentions, the recommended practice is to do all camera-related work on a separate thread from the UI.

It also takes a long time to open the camera, or create a capture session, relatively speaking, so doing those operations not on the UI thread is also a good idea.

That said, as long as you're not losing track of your own app state (so that you don't try to use a camera device you've already closed by accident, for example), there's no reason you can't mix calls to the camera device or capture session from multiple threads. The classes themselves are thread-safe.

来源：https://stackoverflow.com/questions/51973715/close-cameradevice-in-a-seperate-thread