Python Tkinter start stop thread causes cannot start process twice. how to fix?

[Joveice]

So I want to start a thread and stop it with different buttons, which I got working. Now the issue is if you stop the thread and start it again you get "cannot start a process twice", how can I solve this, etc how can I recreate the process after it's been stopped with tkinter buttons.

[reniat]

can you post the relevant code? My GUESS is that you could just create a new instance of whatever thread object you are doing.

e.g.

someThreadAbstraction = None

whenStartButtonClicked():
    someThreadAbstraction = makeThread()
    someThreadAbstraction.start()
    print("Thread started!")
    
whenStopButtonClicked():
    if (someThreadAbstraction): # make sure we don't stop it twice
        someThreadAbstraction.stop
        someThreadAbstraction = None
        print("Thread stopped!")
    

instead of:

someThreadAbstraction = makeThread();

whenStartButtonClicked():
    someThreadAbstraction.start()
    print("Thread started!")
    
whenStopButtonClicked():
    someThreadAbstraction.stop()
    print("Thread stopped!")
    

 

Again, I don't know what threading library you are using, but my guess is that you make a new instance each time you won't have any "cannot start a process twice" issues, which seems to indicate a thread object is being reused when it's not supposed to be.

 

Either way, a relevant code snippet will help give an actual answer instead of a complete guess

[Joveice]

3 minutes ago, reniat said:

can you post the relevant code? My GUESS is that you could just create a new instance of whatever thread object you are doing.

e.g.

someThreadAbstraction = None

whenStartButtonClicked():
	someThreadAbstraction = makeThread()
  	someThreadAbstraction.start()
    print("Thread started!")
    
whenStopButtonClicked():
	if (someThreadAbstraction): // make sure we don't stop it twice
  		someThreadAbstraction.stop
  		someThreadAbstraction = None
        print("Thread stopped!")
    

instead of:

someThreadAbstraction = makeThread();

whenStartButtonClicked():
  	someThreadAbstraction.start()
    print("Thread started!")
    
whenStopButtonClicked():
    someThreadAbstraction.stop()
    print("Thread stopped!")
    

 

Again, I don't know what threading library you are using, but my guess is that you make a new instance each time you won't have any "cannot start a process twice" issues, which seems to indicate a thread object is being reused when it's not supposed to be.

 

Either way, a relevant code snippet will help give an actual answer instead of a complete guess

class MyProcess(object):

    def __init__(self):
        self.process = multiprocessing.Process(target=self.run, args=())
        self.process.daemon = True

    def start(self):
        self.process.start()

    def stop(self):
        self.process.terminate()

    def run(self):
        while True:
            print('hello')
            time.sleep(1)

controller = MyProcess()

def start(event):
    controller.start()
    button_start.config(state='disabled')
    button_stop.config(state='enabled')


def stop(event):
    controller.stop()
    button_start.config(state='enabled')
    button_stop.config(state='disabled')


button_start.bind('<Button-1>', start)
button_stop.bind('<Button-1>', stop)

But someone suggested to add this

 def stop(self):
        self.process.stop()
        self.process = self.process = multiprocessing.Process(target=self.run, args=())

Which worked like I expected it to work when calling start after stopping it.

[reniat]

Glad that you got it working!

 

I don't know if you need 

self.process = self.process = multiprocessing.Process(target=self.run, args=())

instead of just 

self.process = multiprocessing.Process(target=self.run, args=())

but I don't have the deepest python knowledge so maybe that is doing something I'm not aware of (i'd be surprised though)

[Joveice]

19 minutes ago, reniat said:

Glad that you got it working!

 

I don't know if you need 

self.process = self.process = multiprocessing.Process(target=self.run, args=())

instead of just 

self.process = multiprocessing.Process(target=self.run, args=())

but I don't have the deepest python knowledge so maybe that is doing something I'm not aware of (i'd be surprised though)

The bottom works, I didn't try the top one.