Python pyserial和失控的CPU使用率

Question

MacOS 10.7.3, python 2.5

I am using pyserial to open a connection to an external server. The connection is opened as:

HOST = '10.0.0.1'
PORT = '16010'
theURL = 'socket://' + HOST + ':' + PORT
conn = serial.serial_for_url(theURL, baudrate=115200)
conn.timeout = 2

and then the read looks like this:

try:
    while len(rawData) == 0 and self.shutdown == False:
        rawData = conn.readline()
except:
    some error handling code...

The problem is, if I kill the server at 10.0.0.1:16010 the code keeps running, but the cpu usage goes to 100%. No error is thrown, so the except is never entered.

This looks like a problem in pyserial, but maybe someone here has run into this before and knows how to detect the lost connection so the situation can be handled gracefully.

Thanks.

Answer 1

The fact that your CPU usage is pegged probably indicates the the readline call is not blocking to timeout but returns instantly. So if your normal timeout is 2, you could use:

from time import time

try:
    while len(rawData) == 0 and self.shutdown == False:
        before = time()  
        rawData = conn.readline()
        if (len(rawData)==0) and ((time()-before)<2):
              raise Exception("Early readline return.")
except:
    some error handling code...

Answer 2

A very good solution to this can be found here :

class ReadLine:
    def __init__(self, s):
        self.buf = bytearray()
        self.s = s

    def readline(self):
        i = self.buf.find(b"\n")
        if i >= 0:
            r = self.buf[:i+1]
            self.buf = self.buf[i+1:]
            return r
        while True:
            i = max(1, min(2048, self.s.in_waiting))
            data = self.s.read(i)
            i = data.find(b"\n")
            if i >= 0:
                r = self.buf + data[:i+1]
                self.buf[0:] = data[i+1:]
                return r
            else:
                self.buf.extend(data)

ser = serial.Serial('COM7', 9600)
rl = ReadLine(ser)

while True:

    print(rl.readline())

Answer 3

If you're not depending on .readline() you could do it like this:

self.plugin.conn = Serial(..., timeout = 1)
...
if not self.shutdown:
    rawData = self.plugin.conn.read(1)
    if rawData:
        rawData += self.plugin.conn.read(self.plugin.conn.inWaiting())
    else:
        raise Exception("timeout")

I'm not sure if I got your intent right so you might have to adjust...