Raspberry Pi RPi.GPIO error with threated callback

Question

I'm getting stuck with the wait_for_edge function in the Python package RPi. I added multiple event detections for falling gpio's and everything works fine as long as the callback functions contain not a comand like

 os.system("mpc pause") 

Then the script crashes with the error message: "RunetimeError: Error #5 waiting for edge" Does anybody know, what this error message wants to say? Or where I can look up things like this?

To be specific this code works:

def next(channel):
    print "In next"

GPIO.add_event_detect(buttonnext,GP.FALLING,callback=next,bouncetime=200)

os.system("mpc play")

try:
    GPIO.wait_for_edge(buttonstop, GP.FALLING)
    os.system("mpc stop")
except KeyboardInterrupt:
    GPIO.cleanup()
    os.system("mpc stop")
GPIO.cleanup()

But this code doesnt:

def next(channel):
    print "In next"
    os.system("mpc next")

GPIO.add_event_detect(buttonnext,GP.FALLING,callback=next,bouncetime=200)

os.system("mpc play")
try:
    GPIO.wait_for_edge(buttonstop, GP.FALLING)
    os.system("mpc stop")
except KeyboardInterrupt:
    GPIO.cleanup()
    os.system("mpc stop")
GPIO.cleanup()

It crashes after pushing the button connected to the port buttonstop.

Answer 1

Super hacky, but right after the os.system call, if you unbind the event and then rebind it right after, it seems to work.

def next(channel):
    print "In next"
    os.system("mpc next")
    GPIO.remove_event_detect(buttonnext)
    GPIO.add_event_detect(buttonnext,GP.FALLING,callback=next,bouncetime=200)