can't open device: Too many open files Error - linux

Question

Hi I Have Terrible codes in Raspberry Pi 3. I am trying to read 4 RC522 Module and i can do it. But after few minutes I got "can't open device: Too many open files" Error, and my while loop terminated.
I didnt share all the functions. I guess important part is while loop. I create instance in every loop. I guess this is big mistake. I cant add delay. I tried assign null to my object but i got still same error. My Codes are Below
Note: I have 4 SPI address, and i create instance with them.
#!/usr/bin/env python
# -*- coding: utf8 -*-
import time
import sys
import os
import RPi.GPIO as GPIO
import MFRC522
import signal
from time import gmtime, strftime
from time import sleep
import requests
#import xml.etree.ElementTree as ET
#import xmltodict, json
from lxml import objectify
from bs4 import BeautifulSoup
continue_reading = True
GPIO.setmode(GPIO.BOARD)
GPIO.setup(7, GPIO.OUT)
GPIO.setup(37, GPIO.OUT)
GPIO.setup(13, GPIO.OUT)
GPIO.setup(15, GPIO.OUT)
# Capture SIGINT for cleanup when the script is aborted
def end_read(signal,frame):
global continue_reading
print "Ctrl+C captured, ending read."
continue_reading = False
GPIO.cleanup()
kullanici = "xxxx"
sifre = "xxxx"
birim = "xxxx"
ogrKEY = " "
def end_read(signal,frame):
global continue_reading
print "Ctrl+C captured, ending read."
continue_reading = False
GPIO.cleanup()
# Hook the SIGINT
signal.signal(signal.SIGINT, end_read)
# Create an object of the class MFRC522
#
adresler = ["/dev/spidev0.0", "/dev/spidev0.1", "/dev/spidev1.0","/dev/spidev1.1"]
# Welcome message
print "Welcome to the MFRC522 data read example"
print "Press Ctrl-C to stop."
j = 0
# This loop keeps checking for chips. If one is near it will get the UID and authenticate
while continue_reading:
MIFAREReader = None
pin = 0
if j == 100:
j = 0
i = j % 4
if i == 0:
MIFAREReader = MFRC522.MFRC522(adresler[0], 16)
pin = 15
elif i == 1:
MIFAREReader = MFRC522.MFRC522(adresler[1], 18)
pin = 13
elif i == 2:
MIFAREReader = MFRC522.MFRC522(adresler[2], 33)
pin = 7
else:
MIFAREReader = MFRC522.MFRC522(adresler[3], 31)
pin = 37
# Scan for cards
(status,TagType) = MIFAREReader.MFRC522_Request(MIFAREReader.PICC_REQIDL)
# If a card is found
if status == MIFAREReader.MI_OK:
print "Card detected"
# Get the UID of the card
(status,uid) = MIFAREReader.MFRC522_Anticoll()
# If we have the UID, continue
if status == MIFAREReader.MI_OK:
# print "su okuyucudan okundu" % i
# Print UID
print "Card read UID: "+str(uid[0])+","+str(uid[1])+","+str(uid[2])+","+str(uid[3])
# This is the default key for authentication
key = [0xFF,0xFF,0xFF,0xFF,0xFF,0xFF]
# Select the scanned tag
MIFAREReader.MFRC522_SelectTag(uid)
# Authenticate
status = MIFAREReader.MFRC522_Auth(MIFAREReader.PICC_AUTHENT1A, 10, key, uid)
# Check if authenticated
if status == MIFAREReader.MI_OK:
MIFAREReader.MFRC522_Read(10)
ogrKEY = MIFAREReader.returnOGR()
sonuc = parser(ogrKEY)
if sonuc == True:
openTurnsTile(pin)
else:
sonuc = personelKontrol(ogrKey)
if sonuc == True:
openTurnsTile(pin)
MIFAREReader.MFRC522_StopCrypto1()
else:
print "Authentication error"
j = j + 1

Answer 1

When you create the MFRC522 object it actually calls spi.openSPI() but never closes it. This python library is good for single instance but now that you are dealing with multiple instance where FDs are opened, needs to be closed as well using spi.closeSPI(), else you will get the error "Too many open FDs".
To check how many open FDs are there for your PID.