在python中长时间运行的子进程上写入标准输入并从标准输出读取

Question

我有一个长期运行的计算模型，我希望使用STDIN 和STDOUT 控制、提供数据并从中读取数据。在这个外部代码中，有一个控制反馈循环需要每隔 100 毫秒左右从STDIN 获取新数据。

因此，subprocess.communicate() 不合适，因为它等待进程完成。该流程的预计运行时间约为几周。

下面的代码不起作用，因为控制挂在stdout.read() 上并且永远不会回来。

讨论 STDIN 和 STDOUT 的正确方法是什么？

import subprocess as sb


class Foo:
    def process_output(self,values: str) -> ():
        """ gets 7 comma separated floats back from ADC.elf and returns them as a tuple of two vectors """
        floats = [float(f) for f in values.split(',') if values and f]
        # if len(floats) == 7:
        mag = (floats[0], floats[1], floats[2])
        quat = (floats[3], floats[4], floats[5], floats[6])
        return (mag, quat)

    def format_input(self,invals: {}) -> bytes:
        """ takes a dict of arrays and stuffs them into a comma-separated bytestring to send to ADC.elf with a trailing newline"""
        concat = lambda s, f: ''.join([f % x for x in s])
        retval = ''
        retval += concat(invals['mag_meas'], '%3.2f,')
        retval += concat(invals['euler_angle'], '%3.2f,')
        retval += concat(invals['sun_meas'], '%3.2f,')
        retval += concat(invals['epoch'], '%02.0f,')
        retval += concat(invals['lla'], '%3.2f,')
        retval += concat([invals['s_flag']], '%1.0f,')
        retval = retval[:-1]
        retval += '\n'
        return retval.encode('utf-8')

    def page(self,input: {}) -> ():
        """ send a bytestring with 19 floats to ADC.elf.  Process the returned 7 floats into a data struture"""
        formatted = self.format_input(input)
        self.pid.stdin.write(formatted)
        response = self.pid.stdout.read()

        return self.process_output(response.decode())

    def __init__(self):
        """ start the long-running process ADC.elf that waits for input and performs some scientific computation"""
        self.pid = sb.Popen(args=['./ADC.elf'], stdin=sb.PIPE, stdout=sb.PIPE, stderr=sb.PIPE)

    def exit(self):
        """ send SIGTERM to ADC.elf"""
        self.pid.terminate()



if __name__ == "__main__":
    # some dummy data
    testData = {'mag_meas': [1, 2, 3],
                'euler_angle': [4, 5, 6],
                'sun_meas': [7, 8, 9],
                'epoch': [0, 1, 2, 3, 4, 5],
                'lla': [6, 7, 8],
                's_flag': 9
                }
    #initialize
    runner = Foo()
    # send and receive once.
    result = runner.page(testData)
    print(result)
    #clean up
    runner.exit()

Answer 1

不知道如何直接使用 subprocess 执行此操作，但 pexpect 做了完全正确的事情：

import pexpect, os
from time import sleep

class Foo:
    def process_output(self,values: str) -> ():
        floats = [float(f) for f in values.split(',') if values and f]
        # if len(floats) == 7:
        mag = (floats[0], floats[1], floats[2])
        quat = (floats[3], floats[4], floats[5], floats[6])
        return (mag, quat)

    def format_input(self,invals: {}) -> bytes:
        concat = lambda s, f: ''.join([f % x for x in s])
        retval = ''
        retval += concat(invals['mag_meas'], '%3.2f,')
        retval += concat(invals['euler_angle'], '%3.2f,')
        retval += concat(invals['sun_meas'], '%3.2f,')
        retval += concat(invals['epoch'], '%02.0f,')
        retval += concat(invals['lla'], '%3.2f,')
        retval += concat([invals['s_flag']], '%1.0f,')
        retval = retval[:-1]
        retval += '\n'
        return retval.encode('utf-8')

    def page(self,input: {}) -> ():
        formatted = self.format_input(input)
        self.pid.write(formatted)
        response = self.pid.readline()

        return self.process_output(response.decode())

    def __init__(self):

        self.pid = pexpect.spawn('./ADC.elf')
        self.pid.setecho(False)

    def exit(self):
        self.pid.terminate()



if __name__ == "__main__":
    testData = {'mag_meas': [1, 2, 3],
                'euler_angle': [4, 5, 6],
                'sun_meas': [7, 8, 9],
                'epoch': [0, 1, 2, 3, 4, 5],
                'lla': [6, 7, 8],
                's_flag': 9
                }
    runner = Foo()
    i = 0
    while i < 100:
        result = runner.page(testData)
        print(result)
        i += 1
        sleep(.1)



    runner.exit()