In this code, I tried to kill my thread object by setting a variable on it
to False.
Inside the run method of my thread object, it checks a different
variable.
I've already rewritten this code to use semaphores, but I'm just curious
what is going on.
Here's the code:
import logging, threading, time
logging.basicConfig(level=logging.DEBUG,
format="%(threadName)s: %(message)s")
class Waiter(threading.Thread):
def __init__(self, hot_food):
super(Waiter, self).__init__()
self.should_keep_running = True
self.hot_food = hot_food
def run(self):
while self.should_keep_running:
logging.debug("Inside run, the id of should_keep_running is %s."
% id(self.should_keep_running))
self.hot_food.acquire()
def cook_food(hot_food):
i = 5
while i >= 0:
logging.debug("I am cooking food...")
time.sleep(1)
hot_food.release()
logging.debug("Andiamo!")
i -= 1
def main():
hot_food = threading.Semaphore(value=0)
chef = threading.Thread(name="chef", target=cook_food, args=(hot_food, ))
chef.start()
w = Waiter(hot_food)
logging.debug("Initially, the id of w.should_keep_running is %s."
% id(w.should_keep_running))
w.start()
logging.debug("After start, the id of w.should_keep_running is %s."
% id(w.should_keep_running))
# Wait for the chef to finish work.
chef.join()
# Now try to kill off the waiter by setting a variable inside the waiter.
w.should_keep_running = False
logging.debug("Now, the id of w.should_keep_running is %s."
% id(w.should_keep_running))
if __name__ == "__main__":
main()
And here's what I get when I execute it. I have to suspend the process
with CTRL=Z and then kill -9 it.
$ python foo.py
MainThread: Initially, the id of w.should_keep_running is 135527852.
MainThread: After start, the id of w.should_keep_running is 135527852.
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
chef: I am cooking food...
Thread-1: Inside run, the id of should_keep_running is 135527852.
chef: Andiamo!
Thread-1: Inside run, the id of should_keep_running is 135527852.
MainThread: Now, the id of w.should_keep_running is 135527840.
[1]+ Stopped python foo.py
$ kill -9 %1
[1]+ Stopped python foo.py
The memory address of should_keep_running seems to change when I set it
from True to False, and inside the run method, I keep checking the old
location.
I am totally baffled what this means.
Like I said earlier, I already rewrote this code to use semaphores, but
I just want to know what is going on here.
Any explanation is welcome.
TIA
Matt
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