How terminate Python thread without checking flag continuously

Question

class My_Thread(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)

    def run(self):
        print "Starting " + self.name
        cmd = [ "bash", 'process.sh']
        p = subprocess.Popen(cmd,
                     stdout=subprocess.PIPE,
                     stderr=subprocess.STDOUT)
        for line in iter(p.stdout.readline, b''):
            print ("-- " + line.rstrip())
        print "Exiting " + self.name

    def stop(self):
        print "Trying to stop thread "
        self.run = False

thr = My_Thread()
thr.start()
time.sleep(30)
thr.stop()
thr.join()

So i have thread like show above, actually work on windows and process.sh is bash script which run in cygwin and takes around 5 min to finish execution so its not a loop its some simulation proecess

i want to create stop() function in this class so that i can terminate script immediately when i want. after termination i am not expecting any useful result from process.sh script

please can u suggest any method, If possible please give little explanation too..

Answer 1

For your particular example, it's probably easiest to terminate the thread by terminating the subprocess it spawns using the Popen object's terminate() method...

class My_Thread(threading.Thread):

    def __init__(self):
        threading.Thread.__init__(self)
        self.process = None

    def run(self):
        print "Starting " + self.name
        cmd = [ "bash", 'process.sh']
        self.process = p = subprocess.Popen(cmd,
                     stdout=subprocess.PIPE,
                     stderr=subprocess.STDOUT)
        for line in iter(p.stdout.readline, b''):
            print ("-- " + line.rstrip())
        print "Exiting " + self.name

    def stop(self):
        print "Trying to stop thread "
        if self.process is not None:
            self.process.terminate()
            self.process = None

thr = My_Thread()
thr.start()
time.sleep(30)
thr.stop()
thr.join()

...causing a SIGTERM to be sent to bash, and the next call to p.stdout.readline() to raise an exception, which will terminate the thread.

Answer 2

Python threads are not easy to kill, you can use the multiprocessing module (http://docs.python.org/2/library/multiprocessing.html) which is almost the same and it has terminate() function for killing a processes.

Here is a little example, taken from the python docs.

>>> import multiprocessing, time, signal
>>> p = multiprocessing.Process(target=time.sleep, args=(1000,))
>>> print p, p.is_alive()
<Process(Process-1, initial)> False
>>> p.start()
>>> print p, p.is_alive()
<Process(Process-1, started)> True
>>> p.terminate()
>>> time.sleep(0.1)
>>> print p, p.is_alive()
<Process(Process-1, stopped[SIGTERM])> False
>>> p.exitcode == -signal.SIGTERM
True