树莓派PiFmRds切换频率时子进程内存泄漏问题求助

我想用树莓派扩展板的左右按键切换广播频率，用的是PiFmRds库。但切换几次频率后，树莓派就内存耗尽，抛出“Could not allocate memory.”错误。想问旧的子进程是不是一直在运行占内存？如果是，该怎么终止旧进程？

附上代码：

import os
import board
import busio
import adafruit_character_lcd.character_lcd_rgb_i2c as character_lcd
import time
import subprocess
import sys
import digitalio
import threading
import signal


lcd_columns = 16
lcd_rows = 2
i2c = busio.I2C(board.SCL, board.SDA)
lcd = character_lcd.Character_LCD_RGB_I2C(i2c, lcd_columns, lcd_rows)

freq = 103.3

while True:
    try:
        freq = round(freq, 1)
        bashCommand = "sudo ./pi_fm_rds -audio sound.wav -pi 0000 -freq " + str(freq)

        lcd.clear()
        lcd.message = str(freq)
        transmit.send_signal(signal.SIGINT)

        transmit = subprocess.Popen([bashCommand], stdout=subprocess.PIPE, shell=True)

        print(freq)

        while lcd.left_button or lcd.right_button == False:
            if lcd.left_button:
                freq = freq - 0.1
                while lcd.left_button == True:
                    pass
                break
        
            if lcd.right_button:
                freq = freq + 0.1
                while lcd.right_button == True:
                    pass
                break

    except ValueError:
        print(ValueError)
        exit()

你的猜测完全正确——旧的pi_fm_rds子进程根本没被正确终止，一直在后台运行，每次切换频率都会新增一个进程，几次下来就把内存占满了。

代码里的具体问题：

• 第一次循环时transmit变量未定义就调用send_signal，直接触发异常（虽然可能被后续流程掩盖，但逻辑上完全错误）
• 终止旧进程的时机颠倒：你先更新LCD显示，再尝试杀旧进程，最后才启动新进程，而且没有等待旧进程彻底退出就开新的
• 用shell=True启动进程，额外多了一个shell进程占用资源，且未处理子进程的输出缓冲区，可能导致进程阻塞残留

核心思路 #

每次切换频率前，先彻底终止旧的pi_fm_rds进程，释放资源后再启动新进程。

修复后的代码 #

import os
import board
import busio
import adafruit_character_lcd.character_lcd_rgb_i2c as character_lcd
import time
import subprocess
import sys
import signal


lcd_columns = 16
lcd_rows = 2
i2c = busio.I2C(board.SCL, board.SDA)
lcd = character_lcd.Character_LCD_RGB_I2C(i2c, lcd_columns, lcd_rows)

freq = 103.3
transmit = None  # 初始化进程变量，避免首次循环报错

while True:
    try:
        freq = round(freq, 1)
        # 用列表形式传命令，避免shell=True，减少额外进程开销
        cmd_args = ["sudo", "./pi_fm_rds", "-audio", "sound.wav", "-pi", "0000", "-freq", str(freq)]

        lcd.clear()
        lcd.message = str(freq)

        # 终止旧进程：先优雅终止，超时则强制杀死
        if transmit is not None:
            try:
                transmit.send_signal(signal.SIGINT)
                # 等待3秒让进程优雅退出
                transmit.wait(timeout=3)
            except subprocess.TimeoutExpired:
                # 超时就强制杀死
                transmit.kill()
                transmit.wait()  # 确保进程彻底退出
            transmit = None

        # 启动新的传输进程，重定向输出到/dev/null避免缓冲区阻塞
        transmit = subprocess.Popen(
            cmd_args,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL
        )

        print(freq)

        # 优化按键检测循环，降低CPU占用
        while True:
            if lcd.left_button:
                freq -= 0.1
                # 等待按键释放，防止连续触发
                while lcd.left_button:
                    time.sleep(0.05)
                break
            if lcd.right_button:
                freq += 0.1
                while lcd.right_button:
                    time.sleep(0.05)
                break
            time.sleep(0.05)

    except ValueError as e:
        print(e)
        # 退出前清理进程
        if transmit is not None:
            transmit.kill()
            transmit.wait()
        sys.exit()
    except Exception as e:
        # 捕获其他异常（比如进程已退出时调用send_signal）
        print(f"异常: {e}")
        transmit = None

额外优化说明 #

• 按键检测循环加入time.sleep(0.05)，大幅降低CPU占用
• 把输出重定向到DEVNULL，避免子进程因输出缓冲区满而阻塞残留
• 退出程序时主动终止子进程，防止后台残留

内容的提问来源于stack exchange，提问作者Emil12232335