在两个函数间创建Python multiprocessing.Pipe

Question

我使用一个OneWire传感器（ds18b20）来读取温度，然后把这个温度用在一个PI算法中来控制一个SSR继电器。我想在这两个功能之间使用一个管道（Pipe），这样可以快速传递温度数据，让“Reg”函数尽可能快地运行。如果不使用管道，Reg函数就得等温度函数（需要0.75秒）完成，这样输出就会出错……

有人能教我怎么使用管道函数吗？

代码如下：

import time
import RPi.GPIO as GPIO
import os

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BCM)
GPIO.setup(22, GPIO.OUT)


def temperatur(self):
 while True:

    tfile = open("/sys/bus/w1/devices/28-00000433f810/w1_slave")
    text = tfile.read()
    tfile.close()
    secondline = text.split("\n")[1]
    temperaturedata = secondline.split(" ")[9]
    temp2 = float(temperaturedata[2:])
    self.temp = temp2 / 1000
    print self.temp


def reg(self):

  while True:

    ek = self.ref - self.temp
    P_del = self.Kp * ek
    I_del = ((self.Kp * self.Syklustid) / self.Ti) * ek
    Paadrag = P_del + I_del
    if Paadrag > 100:
        Paadrag = 100
    if Paadrag < 0:
        Paadrag = 0    
    print "Paadrag: ", Paadrag, "  Temperatur: ", self.temp
    duty = Paadrag / 100.0
    on_time = self.Syklustid * (duty)
    off_time = self.Syklustid * (1.0-duty)
    print "On_time: ", on_time, "  Off_time: ", off_time
    GPIO.output(22, GPIO.HIGH)
    time.sleep(on_time)
    GPIO.output(22, GPIO.LOW)
    time.sleep(off_time

if __name__ == '__main__':

Answer 1

这段话直接来自Python的官方文档：http://docs.python.org/2/library/multiprocessing.html

from multiprocessing import Process, Pipe

def f(conn):
    conn.send([42, None, 'hello'])
    conn.close()

if __name__ == '__main__':
    parent_conn, child_conn = Pipe()
    p = Process(target=f, args=(child_conn,))
    p.start()
    print parent_conn.recv()   # prints "[42, None, 'hello']"
    p.join()

我发现使用共享状态的效果更好。特别是对于像温度这样的简单数据（我想这只是一个数字，而不是复杂的自定义对象什么的）。这里有一个小例子（你可以在Python文档中找到更多类似的内容）

#import stuff
from multiprocessing import Process, Manager

# Create a shared dictionary of paremeters for both processes to use 
manager = Manager()
global_props = manager.dict()
# SuperImportant - initialise all parameters first!!
global_props.update({'temp': 21.3})

def functionOne(global_props):
    # Do some stuff read temperature
    global_props['temp'] = newVal

def functionTwo(global_props):
    temp = global_props['temp']
    # Do some stuff with the new value

# assign listeners to the two processes, passing in the properties dictionary

handlerOne = functionOne  # This can also be a class in which case it calls __init__()
handlerTwo = functionTwo
processOne = Process(target=handlerOne, 
    args=(global_props))
processTwo = Process(target=handlerTwo, 
    args=(global_props))

# Start the processes running...
processOne.start()
processTwo.start()
processOne.join() 
processTwo.join()