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I would like to stop a running thread from outside a class, how it's possible

For example I have that broadcasting thread:

class BroadcastThread(Thread):
    def __init__(self, converter, websocket_server):
        super(BroadcastThread, self).__init__()
        self.converter = converter
        self.websocket_server = websocket_server
        self.bRun = False
    def run(self):
        try:
            while self.bRun:
                print(self.bRun)
                buf = self.converter.stdout.read1(32768)
                if buf:
                    self.websocket_server.manager.broadcast(buf, binary=True)
                elif self.converter.poll() is not None:
                    break
        finally:
            self.converter.stdout.close()

and I use it as follows from another class

self.broadcast_thread = BroadcastThread(self.output.converter, websocket_server)

and I need to start and stop it using the following methods

 def start_broadcast_stream(self):
     self.broadcast_thread.bRun = True 


 def stop_broadcast_stream(self):
     self.broadcast_thread.bRun = False

The variable bRun is not updated at all by using the functions start_broadcast and stop

andreahmed
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  • What's exactly your problem? – Tobias Brösamle Jan 25 '19 at 11:27
  • The variable bRun is not updated at all by using the functions start_broadcast and stop – andreahmed Jan 25 '19 at 11:29
  • Do you ever call `start()` on your thread? – quamrana Jan 25 '19 at 11:32
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    If it's not updated, you have a very weird Python. Are you sure the problem is not that you run the thread before running `start_broadcast_stream`, so the thread stops before you manipulate the variable? – Amadan Jan 25 '19 at 11:33
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    Did youuse the following call order: `self.broadcast_thread = BroadcastThread(self.output.converter, websocket_server) ; self.broadcast_thread.start_broadcast_stream() ; self.broadcast_thread.start() ; # do something else ; self.broadcast_thread.stop_broadcast_stream()`? Sorry it's so ugly, `;` means a new line here - I cannot do this in comments. – Tobias Brösamle Jan 25 '19 at 11:37
  • @Amadan actually that was the problem... how can I make it run forever depending on the variable.. bRun.. can you post an answer ? – andreahmed Jan 25 '19 at 11:38
  • See the dupe. The trick is - have an infinite loop around your while, and use `Event` or `Condition` to make sure your loop doesn't spin while "stopped". – Amadan Jan 25 '19 at 11:45

1 Answers1

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That is the common way in python and should work, but it will have the chance of stopping only every time the condition of the while is evaluated. You must guarantee the inside of the loop does not block, or takes very long time to run.

If you want to be able to cancel inside the loop, you need to slice things thinner (for example read 10 times a 1/10th of the data) and intercalate several checks of the bRun condition + breaks between them. Not pretty...

Edit: For added safety, bRun could be a Threading.Event, but I don't see the problem in this simple case.

agomcas
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