Why does the instance need to be recreated when restarting a thread?

Question

Imagine the following classes:

Class Object(threading.Thread):
    # some initialisation blabla
    def run(self):
        while True:
            # do somet         


        

Answer 1

The reason why threading.Thread is implemented that way is to keep correspondence between a thread object and operating system's thread. In major OSs threads can not be restarted, but you may create another thread with another thread id.

If recreation is a problem, there is no need to inherit your class from threading.Thread, just pass a target parameter to Thread's constructor like this:

class MyObj(object):
    def __init__(self):
        self.thread = threading.Thread(target=self.run)
    def run(self):
        ...

Then you may access thread member to control your thread execution, and recreate it as needed. No MyObj recreation is required.

Answer 2

I believe, that has to do with how Thread class is implemented. It wraps a real OS thread, so that restarting the thread would actually change its identity, which might be confusing.

A better way to deal with threads is actually through target functions/callables:

class Worker(object):
    """ Implements the logic to be run in separate threads """
    def __call__(self):
        #  do useful stuff and change the state

class Supervisor():
    def run(self, worker):
        thr = None
        while True:
            if not thr or not thr.is_alive():
                thr = Thread(target=worker)
                thr.daemon = True
                thr.start()
            thr.join(1)  # give it some time

Answer 3

See here: http://docs.python.org/2/library/threading.html#threading.Thread.start

It must be called at most once per thread object. It arranges for the object’s run() method to be invoked in a separate thread of control.

This method will raise a RuntimeError if called more than once on the same thread object.

A thread isn't intended to run more than once. You might want to use a Thread Pool