串口不重写Python的code工作 [英] Serial port does not work in rewritten Python code

问题描述

我有一个Python程序，在数据库中读取一个Arduino并将其存储一些参数。串行端口设置和使用这样的：

I have a Python program that reads some parameters from an Arduino and stores it in a database. The serial port is set up and used like this:

ser = serial.Serial(port=port, baudrate=9600)
ser.write('*')
while 1 :
    ser.write('*')
    out = ''
    # Let's wait one second before reading output (let's give device time to answer).
    time.sleep(1)
    while ser.inWaiting() > 0:
        out += ser.read(1)
    if out != '': 
        etc ... handling data

（Arduino的设置，所以当它收到一个明星，它发回的数据串）。我想改写这个作为的守护，所以我使用Python守护进程库。在的init 双组分，我只是定义端口名称，然后：

(The Arduino is set up so when it receives a star, it sends back a data string.) I would like to rewrite this as a daemon, so I am using the python-daemon library. In the init-part, I just define the port name, and then:

def run(self):
    self.ser = serial.Serial(port=self.port,baudrate=9600)
    while True:
        self.ser.write('*')
        out = ''
        # Let's wait one second before reading output (give device time to answer).
        time.sleep(1)
        while self.ser.inWaiting() > 0:
            out += self.ser.read(1)
        if out != '':
            etc ...

一切都是平等的，但我现在在做一个App-对象中的串行处理。第一个版本运行正常，当我尝试运行后，我得到

Everything is equal, except that I am now doing the serial handling within an App-object. The first version runs fine, when I try to run the latter, I get

File "storedaemon.py", line 89, in run
 while self.ser.inWaiting() > 0:
 File "/usr/lib/python2.7/dist-packages/serial/serialposix.py", line 435, in inWaiting
 s = fcntl.ioctl(self.fd, TIOCINQ, TIOCM_zero_str)
 IOError: [Errno 9] Bad file descriptor

我不能看到发生了什么变化 - 除了我已经抛出一个新的对象内部的code。我曾经尝试都做初始化中的的init 并在运行，但我结束了相同的结果。

I am not able to see what has changed - except that I have tossed the code inside a new object. I have tried both to do the initialisation in init and in run, but I end up with the same result.

（完整的脚本可在 hhv3.sickel.net/b/storedata.py 和 hhv3.sickel.net/b/storedaemon的.py ）

推荐答案

在你的应用程序的系统守护进程，所有的文件处理程序关闭除标准输入，标准错误和标准输出。这包括的/ dev /日志，然后失败与FD的错误（所以它看起来像这样无关与串行FD，而是和处理程序的连接插座）。

During the daemonization of your app, all file handlers are closed except stdin, stderr and stdout. This includes the connection to /dev/log, which then fails with the fd error (so it looks like this has nothing to do with the serial fd, but instead with the handler's socket).

您需要或者本FD添加到排除列表：

You need either to add this FD to the exclusion list:

class App():
    def __init__(self):
        ...
        self.files_preserve = [handler.socket]
        ...

或者，设置处理程序的守护进程分叉后：

Or alternatively, set up the handler after the daemon process forked:

class App():
    def run(self):
        handler = logging.handlers.SysLogHandler(address = '/dev/log')
        my_logger.addHandler(handler)
        my_logger.debug(appname+': Starting up storedata')
        ...

这两个版本在我的测试中运行良好。

Both version ran fine during my tests.

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