usbManager openDevice call fails after several hundred successful attempts - usb

Question

I'm using usbmanager class to manage USB host on my android 4.1.1 machine.
all seems to work quite well for a few hundreds of transactions until (after ~ 900 transactions) opening the device fails, returning null without exception.
Using a profiler it doesn't seem to be a matter of memory leakage.
this is how I initialize the communication from my main activity (doing this once):
public class MainTestActivity extends Activity {
private BroadcastReceiver m_UsbReceiver = null;
private PendingIntent mPermissionIntent = null;
UsbManager m_manager=null;
DeviceFactory m_factory = null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(ACTION_USB_PERMISSION), 0);
IntentFilter filter = new IntentFilter(ACTION_USB_PERMISSION);
filter.addAction(UsbManager.ACTION_USB_DEVICE_DETACHED);
m_UsbReceiver = new BroadcastReceiver() {
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
if (UsbManager.ACTION_USB_DEVICE_DETACHED.equals(action)) {
UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);
if (device != null) {
// call your method that cleans up and closes communication with the device
Log.v("BroadcastReceiver", "Device Detached");
}
}
}
};
registerReceiver(m_UsbReceiver, filter);
m_manager = (UsbManager) getSystemService(Context.USB_SERVICE);
m_factory = new DeviceFactory(this,mPermissionIntent);
}
and this is the code of my test:
ArrayList<DeviceInterface> devList = m_factory.getDevicesList();
if ( devList.size() > 0){
DeviceInterface devIf = devList.get(0);
UsbDeviceConnection connection;
try
{
connection = m_manager.openDevice(m_device);
}
catch (Exception e)
{
return null;
}
The test will work OK for 900 to 1000 calls and after this the following call will return null (without exception):
UsbDeviceConnection connection;
try
{
connection = m_manager.openDevice(m_device);
}

Answer 1

You might just run out of file handles, a typical limit would be 1024 open files per process.
Try calling close() on the UsbDeviceConnection, see doc.
The UsbDeviceConnection object has allocated system ressources - e.g. a file descriptor - which will be released only on garbage collection in your code. But in this case you run out of ressources before you run out of memory - which means the garbage collector is not invoked yet.

Answer 2

I had opendevice fail on repeated runs on android 4.0 even though I open only once in my code. I had some exit paths that did not close the resources and I had assumed the OS would free it on process termination.
However there seems to be some issue with release of resources on process termination -I used to have issues even when I terminated and launched a fresh process.
I finally ensured release of resources on exit and made the problem go away.