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我正在用 Python 为 USB HID 设备编写 Linux 驱动程序。设备有两种发送数据的方式，这两种方式都是必需的：特征报告（同步）和输入报告（异步）。使用 hidapi Cython 库，我只有一个设备实例可以使用，但我需要为 hid.read() 设置一个监听器，它将持续运行并允许应用程序随意调用同步方法来发送功能报告。

目前我在一个线程中有监听器，在另一个线程中有同步调用。当我运行程序时，我的同步调用没有发生，尽管如果我从不启动监听器它们工作正常；所以看起来监听器线程正在接管。

下面是一段令人不安的代码：

应用程序.py

# app.py
import threading
import time
import myhiddriver

# Code that sets mydevice

class Reader:
  def start(self, device):
    self.requests = myhiddriver.DeviceRequest(device)
    # Wait a bit before firing, for testing
    time.sleep(3)
    self.requests.request_swipe_card()

  def start_listener(self, device):
    self.listener = myhiddriver.DeviceListener(device)

reader = Reader()
thread1 = threading.Thread(target=reader.start, args=(mydevice,))
thread1.daemon = True
thread2 = threading.Thread(target=reader.start_listener, args=(mydevice,))
thread2.daemon = True
thread1.start()
thread2.start()

# Keep this puppy running
while True:
  pass

myhiddriver.py

import threading

LOCK = threading.Lock()

class DeviceRequest:
  def __init__(self, device):
    # Lock it up first
    LOCK.acquire()
    self.device = device
    LOCK.release()

  def request_swipe_card(self):
    # Lock this up too
    LOCK.acquire()
    self.device.set_feature_report(insert data here)
    LOCK.release()

class DeviceListener:
  def __init__(self, device):
    # Lock me up
    LOCK.acquire()
    self.device = device
    self.start_listener()
    LOCK.release()

  def start_listener(self):
    while True:
      # Should I be locking this up?
      LOCK.acquire()
      data = self.device.read(255)
      LOCK.release()
      if data:
        print data
      else:
        pass

我的问题：为什么我的同步调用（request_swipe_card）没有通过？或者，我怎样才能更好地构建它以拥有一个无穷无尽的监听器以及对同一个对象进行同步调用的能力？

4

1 回答 1

3

从代码的外观来看，这是因为您将其锁定

当状态解锁时，acquire() 将状态更改为锁定并立即返回。当状态被锁定时，acquire() 会阻塞，直到另一个线程中对 release() 的调用将其更改为未锁定

这是问题所在：

class DeviceListener:
  def __init__(self, device):
    LOCK.acquire() # first you lock it up
    self.device = device
    self.start_listener()
    LOCK.release()

  def start_listener(self):
    while True: # because of the loop, the lock wouldn't get release even if the LOCK below doesn't exist
      LOCK.acquire() # it end up blocking here and oops, it locked up xD 
      data = self.device.read(255) # so it wouldn't be able to read here
      LOCK.release()
      if data:
        print data
      else:
        pass

当request_swipe_card最终在另一个线程中被调用时，它最终也会在那里阻塞

  def request_swipe_card(self):
    LOCK.acquire() # right here xD
    self.device.set_feature_report(insert data here)
    LOCK.release()
于 2014-11-08T22:08:48.093 回答