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I'm using the great "evdev" library to listen to a USB barcode reader input and I need to detect if the device suddenly gets unplugged/unresponsive because otherwise the python script reading the loop goes to 100% cpu usage on a single thread and slowly starts to eat all available memory which leads to the entire system crashing after a bit.

The idea is to detect when the device is unplugged and kill the current script leading to supervisor trying to restart it until the device is plugged back in/becomes responsive.

The code I'm using to read the input is as follows:

devices = map(InputDevice, list_devices())

keys = {
    2: 1,
    3: 2,
    4: 3,
    5: 4,
    6: 5,
    7: 6,
    8: 7,
    9: 8,
    10: 9,
    11: 0,
}
dev = None
for d in devices:
    if d.name == 'Symbol Technologies, Inc, 2008 Symbol Bar Code Scanner':
        print('%-20s %-32s %s' % (d.fn, d.name, d.phys))
        dev = InputDevice(d.fn)
        break

if dev is not None:
    code = []
    for event in dev.read_loop():
        if event.type == ecodes.EV_KEY:
            if event.value == 00:
                if event.code != 96:
                    try:
                        code.append(keys[event.code])
                    except:
                        code.append('-')
                else:
                    card = "".join(map(str, code))
                    print card

                    code = []
                    card = ""

So how would I go about doing this the proper way?
A way I though that might work would be a second script that's run from cron every 1-5 min that checks if said device is still available, if it's now, grab process id from some file and kill the process that way but the problem with this method is that if the device is unplugged and then plugged back between the checks the "checker" script thinks everything is okay while the main script is slowly crashing - it doesn't re-activate after an "unplugging"

4

1 回答 1

9

python-evdev作者在这里。知道自己的工作对其他人有用是一种很棒的感觉。谢谢你！

您绝对应该查看 linux 的设备管理器 - udev。每当添加或删除设备时，linux 内核都会发出事件。要在 Python 程序中侦听这些事件，您可以使用pyudev，它是一个出色的、基于 ctypes 的对 libudev 的绑定（请参阅监控部分）。

evdev这是与 with 一起使用的示例pyudev：

import functools
import pyudev

from evdev import InputDevice
from select import select

context = pyudev.Context()
monitor = pyudev.Monitor.from_netlink(context)
monitor.filter_by(subsystem='input')
monitor.start()

fds = {monitor.fileno(): monitor}
finalizers = []

while True:
    r, w, x = select(fds, [], [])

    if monitor.fileno() in r:
        r.remove(monitor.fileno())

        for udev in iter(functools.partial(monitor.poll, 0), None):
            # we're only interested in devices that have a device node
            # (e.g. /dev/input/eventX)
            if not udev.device_node:
                break

            # find the device we're interested in and add it to fds
            for name in (i['NAME'] for i in udev.ancestors if 'NAME' in i):
                # I used a virtual input device for this test - you
                # should adapt this to your needs
                if u'py-evdev-uinput' in name:
                    if udev.action == u'add':
                        print('Device added: %s' % udev)
                        fds[dev.fd] = InputDevice(udev.device_node)
                        break
                    if udev.action == u'remove':
                        print('Device removed: %s' % udev)
                        def helper():
                            global fds
                            fds = {monitor.fileno(): monitor}
                        finalizers.append(helper)
                        break

    for fd in r:
        dev = fds[fd]
        for event in dev.read():
            print(event)

    for i in range(len(finalizers)):
        finalizers.pop()()
于 2013-05-11T18:35:41.920 回答