terminate a USBdetector Thread using monitor from pyudev

Question

I have a python script that I'm running on a remote device. There will be two different threads created. The first thread is created to monitor for USB connections to the device.

class USBDetector(threading.Thread):
    ''' Monitor udev for detection of usb '''

    def run(self):
        ''' Runs the actual loop to detect the events '''
        self.context = pyudev.Context()
        self.monitor = pyudev.Monitor.from_netlink(self.context)
        self.monitor.filter_by(subsystem='usb')
        self.monitor.start()
        for device in iter(self.monitor.poll, None):
            if device.action == 'add':
                # some action to run on insertion of usb

I've tried to insert a break statement if a global variable state changes. But it didn't work. something simple like

if TERMINATE == True:
    break

I looked at https://pyudev.readthedocs.io/en/latest/api/pyudev.html and through the reading it looks like this section of code

for device in iter(self.monitor.poll, None):
            if device.action == 'add':
            # some function to run on insertion of usb

is an endless loop, unless a timeout is inserted instead of None. I want to kill the thread when the other thread ends. If I give the quit command for my main thread, this usbdetector just keeps running. Any suggestions on how to stop it?

(UPDATE)

Hey,

sorry I went with a low tech way of solving my problem for now.

If anyone knows how to break out of this for loop without the need of a second loop, let me know

def run(self):
        ''' Runs the actual loop to detect the events '''
        global terminate
        self.rmmod_Module()
        self.context = pyudev.Context()
        self.monitor = pyudev.Monitor.from_netlink(self.context)
        self.monitor.filter_by(subsystem='usb')
        self.monitor.start()
        count = 0
        while not terminate:
            count = count + 1
            print count
            for device in iter(partial(self.monitor.poll, 3), None):
                if device.action == 'add':
                     # some function to run on insertion of usb

obviously I have the for loop nested in a while loop waiting for terminate to be true. Its simple and works, however would still like to know if there is a way to kick out of the for device in iter() loop.

Answer 1

This may not be the direct answer you are looking for. Instead of synchronously monitoring the USB ports by polling, why not use asynchronous callbacks as seen in the following pyudev monitoring device guide under section Asynchronous monitoring¶.

monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by('block')
def log_event(action, device):
   if 'ID_FS_TYPE' in device:
       with open('filesystems.log', 'a+') as stream:
           print('{0} - {1}'.format(action, device.get('ID_FS_LABEL')), file=stream)

observer = pyudev.MonitorObserver(monitor, log_event)
observer.start()

From the code snippet you may receive multiple callbacks for a single USB device action, as it may recognise a single USB device as multiple devices. Putting this all together now you could do something as the following.

class USBDetector():
''' Monitor udev for detection of usb '''

def run(self):
    ''' Runs the actual loop to detect the events '''
    self.context = pyudev.Context()
    self.monitor = pyudev.Monitor.from_netlink(self.context)
    self.monitor.filter_by(subsystem='usb')
    self.observer = pyudev.MonitorObserver(self.monitor, self.usbDeviceEventHandler)
    self.observer.start()

def usbDeviceEventHandler(self, action, device):
    if device.action == 'add':
       # some function to run on insertion of usb

You may get multiple callbacks for a single usb action, so you could implement thread locking with Thread.lock() and accessing and editing a time variable and only accept new callbacks every second. I hope this helps, sorry for the late reply.