Python evdev检测设备未插入

Question

我正在使用伟大的"evdev"库来听USB条形码阅读器输入，我需要检测设备是否突然拔出/无响应，否则python脚本读取循环在单个线程上达到100%的cpu使用率，并慢慢开始吃所有可用的内存，导致整个系统崩溃后一点。

这个想法是检测设备何时拔出并杀死当前脚本，导致管理员试图重新启动它，直到设备重新插入/响应。

我用来读取输入的代码如下:

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 = ""

那么我该如何以正确的方式去做呢?
我虽然这可能的工作方式将第二个脚本的运行从cron每1 - 5分钟检查说设备仍然可用,如果是现在,抓住一些文件和杀死进程的进程id,但这种方法的问题是,如果设备是不插电,然后插回检查"检验员"脚本之间的认为一切都是好的在主脚本慢慢崩溃——它不会重新激活后"拔掉"

Answer 1

python-evdev作者。知道自己的工作对别人有用是一种很棒的感觉。谢谢你!

你一定要看看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程序中监听这些事件，您可以使用pyudev，它是一个出色的、基于ctypes的绑定到libdev(请参阅监视部分)。

下面是一个使用evdev和pyudev的例子:

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()()